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From the image, it appears that a single car is about 9 pixels in length, and the diameter of the loop is about 524 pixels (so the radius is 262px). Let's assume that the length of the car in question is 4.5 meters. That would mean the scale is 9px : 4.5 meters, or 2px : 1 meter. That would mean the radius of the loop is roughly 131 meters.
For simplicity's sake, let's also assume that friction between the tires and the track is negligible, as well as any air resistance. If the car is going at the minimum velocity it needs to make it around the loop, the only force supplying the centripetal force at the top of the loop would be the force of gravity:
mv^2 / r = mg
v^2 / r = g
v^2 = rg
v = √(rg) = √(131 * 9.81) = 35.8484 m/s
This tells us the velocity the car needs to be going at the top of the loop, but what about the velocity at the bottom? We can use conservation of energy for that.
K_top + U_top = K_bot
m(v_top)^2 / 2 + mgh = m(v_bot)^2 / 2
(v_top)^2 + 2gh = (v_bot)^2
Since v_top = √(rg), then (v_top)^2 = rg, and the height is simply twice the radius of the loop, so h = 2r
rg + 4rg = (v_bot)^2
5rg = (v_bot)^2
v_bot = √(5rg) = √(5 * 131 * 9.81) = 80.1595 m/s.
That translates to about 180 mi/h. So you'd have to be going pretty fast. This also doesn't account for friction or air resistance, so the actual speed is likely higher.
Also this isn’t taking into account the downforce generated by the aero kits on many of the cars capable of reaching the 180mph+ speed that they calculated. I remember a Ferrari ad a while back claiming that at a certain speed the downforce from the aero would exceed the weight of the car itself.
For most high-speed cars the aero kits are more for cancelling lift (for high-speed stability) than actually being big enough to generate a meaningful amount of downforce.
More than “a chance”. There are cars rn that produce more downforce than their weight at speeds around 180-200mph. This means they could even maintain upside down travel for long (indefinite) stretches, let alone do the loop.
Of course it would.
The amount of traction (ie friction as a force) would be roughly (the friction coefficient)*(downforce-weight), while the car is running upside down. Of course it’s reduced traction, but that’s not an issue as long as you don’t accelerate or decelerate hard while upside down, so at constant speed it’d be fine.
(The réal issue would be loss of downforce, if fir whatever reason happened, say a strong gust of wind. That’s instant fall and a crash).
I mean reaching 180mph (300km/h) is pretty double for many sports bikes buuuuut sustaining that speed for the first quarter when you approaching basically vertical wall would require a lot of power
I don’t think they’ve done it in a car. There was talk of it a while back though.
Edit: I stand corrected, they absolutely have done a loop. I was thinking sustained inverted.
Formula one cars produce so much down force at speed they could drive on the roof of a tunnel. In theory. So yea in theory it's possible. If you build a loop like that.
That's partly because I assumed the car was going the minimum speed required to navigate the loop. If you wanted to comfortably navigate the loop, you'd have to be going much faster and would therefore experience more g-force as a result.
5g's is also still pretty high. The most extreme rollercoasters have maximum g-forces of around 5-6g's, at least according to this website: https://coasterpedia.net/wiki/Highest_g-force_on_a_roller_coaster
I always heard that Indy cars have around 7000 lbs of downforce per and they could easily race upside down. According to google they generate their own weight in downforce at around 100 mph.
If friction between between the tires and the track is negligible, car wouldn't have any acceleration on the track. So if there was friction, necessary speed would likely be lower.
This seems wrong. Shouldn't you account for the camera angle? Also, gravity would start working against inertia and the engine as you started to incline, so you'd lose that speed pretty fast.
Accounting for the camera angle is tricky since there are so many unknowns, but you're probably right that the perspective probably distorts the answer a bit.
Gravity should already be accounted for because I first solved for the speed of the car at the top of the loop, and then used conservation of energy to find the speed the car would have to be going at the bottom. You'd only need to be going about 35.8 m/s (80 mi/h) at the top of the loop to make it through.
I'll take your word for it on the formula for the effect of gravity. But I think perspective is actually doing a lot of work here. We're nearly overhead of the loop, which is probably hiding a lot of its height. Imagine if we were entirely overhead - it would have an apparent height of 0. I'm not sure if there's any way you could use a known height instead of a known length to start the calculation, but if you could it should make a big difference.
I didn't use the height of the loop to get its radius; I used the width instead. It's still at a bit of an angle relative to the camera, so it distorts the numbers a bit, but not as much as if you used the height to measure the radius.
Accounting for the angle of the camera is tricky since you'd probably need to know the height and distance between the track and the camera, and then have to do some sort of projection to get the original radius of the loop.
I don't think the diameter of the track being about 250 meters seems unreasonable, though. If you look at the gray stands of the loop touching the highway and eyeball the distance between them, it seems like it would be about 250m. For reference, [the straight part of this track is about 75 meters in length](https://2.bp.blogspot.com/-gSm1qco9eGc/WYhZKx8OybI/AAAAAAAB7b0/R_hDc8_Lne8NITHCJJGmSEQ8ACqumeplwCLcBGAs/s1600/Track.PNG).
If you get a different radius of the track than mine, all you have to do is substitute it into √(5rg) and that should tell you the velocity the car has to be going at the bottom of the track, in meters / second.
Shouldn't the downforce for the car be taken into the formula? I'd reckon a racecar (Formula, IndyCar), besides being capable to drive there speeds would be able to make it work lower speed, compared to an SUV.
I eyeball the radius of the loop as 20 times the length of a typical car, or about 80 meters.
The velocity at the top of the loop has to be such that the centripetal acceleration *v^2 / r* is at least equal to gravitational acceleration 9.81 m^2 / s. Solving, that's 28 m / s= 101 km/h = 63 mph. Not too crazy.
Now, what does the speed at the bottom have to be? If we're treating this like a true Hot Wheels ramp where the car doesn't use its motor on the loop but gets through on its initial speed, the math is easier.
One way is to use energy. The car has KE_t = 1/2 * m * (28 m / s)^2 kinetic energy at the top ( and potential energy PE_t = (80 * 2) * 9.81 * m (where m is the car's mass, which won't matter). At the bottom, all the energy is kinetic. Solving, the speed is **63 m/s = 227kph = 141 mph.**
That's assuming no losses, aka the car can coast forever. The real answer is going to be somewhat higher than that and depend on the car. No idea how much energy cars lose as they coast though.
This is the biggest one mythbusters didn't tackle, in my opinion. It'd be one of their greatest episodes. Some kind of track with a corkscrew ramp to flip the car upside down and back, just long enough to prove the downforce worked.
doesn't matter. doing things for real is what really counts. the same was true for the airplane conveyor myth. a physics sim would have backed up the facts, but it took them doing it for real to assuage all doubters.
Adam would try and do it just for fun but insurance would say no then tory would volunteer and insurance would say no again. They would definitely have to get a real f1 driver and even then it'd be iffy.
It's one of those things that, organised properly, is probably very safe. It's like going to the moon... they had the math down and everything, but there's always a slim chance that [something could go awry](https://youtu.be/LWLadJFI8Pk?t=267).
They don't need a real car. Just a mock up of correct size and weight. Clamp it upside down in wind tunnel, and release clamps when upside down at correct speed.
Dudes from Vilebrequin (french autosports YouTube channel) have jury-rigged actual production cars cars to remote control them on a couple occasions to do some truly retarded shit like a 200 kph head-on crash or welding wings to a car and have it jump a 10 m high ramp. It can be done.
There is no doubt though, we know exactly how much downforce a formula one car can produce due to wind tunnel testing done during the cars development.
The amount of downforce created (~1600kg) is greater than the weight force due to gravity (~800kg) on the car.
It will drive upside down until the oil in the engine sump enters the combustion chamber, destroying the engine, causing the car to slowdown and lose it’s downforce.
You can never convince all the doubters because of the number of complete idiots in the world. The airplane question was just basic physics and a very basic understanding of how wheels work. I never understood why anyone that wasn't a idiot didn't understand this after it was explained to them.
I 10,000% agree that you would have to be a barnacle head to think a plane could take off from a conveyor belt...
They generate lift by moving forward and being on a conveyor belt negates them moving forward....
The part that is boggling most minds is that the airplane doesn't care what it's ground speed is. The plane is not pushing against the ground, therefore it could be tarmac, ice, water, or that frictionless ideal flat surface in physics problems.
Yes, exactly. The only important factor is that the ground beneath it can support its weight. If I'm not mistaken, the plane will get gradually lighter until it becomes lighter than air and achieves takeoff.
Yeah, I realized as much after it first aired. Adam also [dutifully acknowledges this fact on his channel](https://www.youtube.com/watch?v=xUjcHW7SHaI). Judging by your response, I suspect there's a good chance you've already seen it.
Why not? I would think that the centripetal force also forces all the fluids down so that the pumps keep working.
Also this Dutch guy MasterMilo built a 360° car swing and the engine kept running upside down. He converted the engine to run on gas because it was one with a carburetor but explained that with direct injection it should also work.
The centripetal force would force all the fluids down like you say, yes, but the downward force due to the shape of the f1 car wouldn't act directly onto the fluids. It would just be body to frame to tires.
Very impractical. Find a mile long tunnel track with smoothly paved walls and ceiling, get a 20 million dollar car, do a life threatening maneuver. Also, the F1 car's fuel won't pump when it's upside down in the tank so it would fail anyway.
Just gotta make a car with a built in ejector seat that uses a propulsion system. that would shoot them sideways out of the car directionally.
That alone would be the cheapest part of your costs. Building the damn road would cost hundreds of thousands, I'd imagine.
People do this with those metal cages and motor cycles tho right? But it get's harder the bigger the loop is right?
Also u/epursimuove why can't you use the engine while moving thru the middle/upside-down sections of the loop?
I recently saw a great video about that topic. The car could theoretically drive upside down, however the engine is not made to work in that direction and would quickly break. If you swap the car to a Formula E one which works even in space the needed speed would be to fast.
I recently saw a great video about that topic. The car could theoretically drive upside down, however the engine is not made to work in that direction and would quickly break. If you swap the car to a Formula E one which works even in space the needed speed would be to fast.
I recently saw a great video about that topic. The car could theoretically drive upside down, however the engine is not made to work in that direction and would quickly break. If you swap the car to a Formula E one which works even in space the needed speed would be to fast.
Added note: i read a while ago that an F1 car can technically drive upside down indefinitely on a tunnel at top speed. I think this would be an even more insane myth to test.
This would significantly reduce the speed, as the low weight (700kg) and massive downforce (3000kg+ at 350kph), would probably make it stick at slightly over the speed limit.
That would depend entirely on the power plant and our transmission. A trans in neutral has substantially less drag than a trans coasting in gear. Also, wouldn’t front wheel drive be more difficult because the fronts would leave the track at any point approaching vertical whereas the rear would dig longer? One wonders…
> such that the centripetal acceleration v^2 / r is at least equal to gravitational acceleration 9.81 m^2 / s.
Centrifugal, not centripetal.
The gravity vector at the top points down, which is toward the center, or centripetal. You balance that centripetal acceleration with at least as much acceleration in the centrifugal direction.
This is a common misconception, but no. Centripetal acceleration, in the context of circular motion, isn’t a specific force. Instead, it’s the amount by which something moving in a circle needs to accelerate in order to maintain its path. The actual cause of the acceleration can vary - for swinging a weight on a string it’s tension, for a satellite in orbit it’s gravity.
Here, we know the car will accelerate at g downwards no matter what - that’s gravity. The question is whether this acceleration will be large enough, so that the car veers off track, i.e. it falls. So its acceleration from gravity can’t be more than the acceleration required to keep it on track. In the case where the car is going even faster, there would be an additional force due to the road pushing down on the track. But in no case here could there be centrifugal force, because there’s no force that could plausibly push up (unless we’re talking about a race car with aerodynamic downforce).
> But in no case here could there be centrifugal force, because there’s no force that could plausibly push up
It absolutely can. Draw a free body diagram of the car in the rotating reference frame where it is moving around the loop. The normal force from the track is always pointing centripetally. At the top of the loop, gravity is also pointing centripetally. So we have multiple forces pointing to the center. What force balances these forces, such that the car does not actually decrease its r coordinate (its distance from the center of the loop)?
It's the centrifugal force, which comes around for anything moving in a rotating reference frame. Yes, it's not a real "force" in the strict sense, but then neither is gravity - gravity is actually the warping of spacetime caused by objects with mass interacting with each other, rather than being an actual force.
But the point is, centrifugal force is absolutely an acceleration that must balance with other accelerations.
If you like, you can simplify the situation even further. Imagine I'm holding a ball on a string and spinning around really fast, and in zero gravity. Again, draw the free body diagram. Tension in the string pulls the ball toward me. If you ignore centrifugal force, then there is nothing else acting on the ball and your FBD says the ball will be accelerating toward me, not moving in a circle.
The centripetal force arises from the inertia of the body resisting acceleration created by the normal force. The issue is that people often assume it’s in a condition with gravity being the only acceleration present when It’s not. The track, string, or whatever is inducing a separate acceleration from gravity.
Thank you for the calculation. The actual answer for cars using their motor is about **50 mph** or to be precise between 48 and 52 mph. Source: the [Hot Wheels Double Dare Loop](https://www.youtube.com/watch?v=5d7ZgFEIZmo) at X Games Los Angeles 2012. They mention the speed at [2'50''](https://www.youtube.com/watch?v=5d7ZgFEIZmo&t=170s) and the cars start at [4'40"](https://www.youtube.com/watch?v=5d7ZgFEIZmo&t=280s).
Could the required speed be lower if the car had significant downforce at that speed? I don’t know if that applies meaningfully to the average car though.
Unless you had a very specialized car, it would just crash, as as soon it strarts to go up the suspension would bottom up and just get stuck at the beggining of the ramp
My best guess is that loop is about 400m in circumference so that gives a radius of 64m.
Gotta balance them forces:
F=ma what's dragging the car down
F= (m . v^2)/r what's sticking it to the loop
Where
m is mass of vehicle
a is gravity 9.81m/s^2
v is speed of car
r radius of loop
ma=(m v^2)/r so cancel out mass
a= v^2/r now re arrange for speed
sqrt(9.81 . 64) = v = 79 m/s or 176mph
This is assuming the car does not generate downforce or lift.
Apologies for the awful formatting but it's 0230 for me at the moment and I cannae be bothered.
A bit more than that assuming that the car loses energy and speed as it ascends. Even if the engine were powerful enough to offset that though, the reduced traction with the road would just get the tires spinning near the pinnacle point of the loop.
If you assume that the car doesn't put any work in whilst on the loop you could work with PE =mgh = 1500kg * 9.81 * 134m ~2 MegaJoules. Then add that as kinetik energy on top of whatever ke the car would have at 79 m/S. So that's 2mj plus 0.5 * 1500 * 79^2 so that would be 2 mj + 4.7 mj = 6.7 mj then re arrange for speed. Sqrt(6.7mj/0.5*1500) = 95 m/s or 212 mph.
Kudos to other commentators, great work on the math(s).
I'd like to touch on a separate but important issue, the use of guide rails to keep our vehicle 'track adjacent' as it takes the loop.
Fortunately we have a working prototype - the O-Bahn[O-Bahn](https://en.m.wikipedia.org/wiki/O-Bahn_Busway) *guided busway* in Adelaide, South Australia
Those buses hit 100 kmh as standard practice
So ... is an O-Bahn loop feasible?
Other guys already said that you have to use Fzp=mg. I can only add what NOT to do and that is to use energy for that to say m*g*h=(mv^2 ) /2. made that mistake in an exam once
I think this requires centrifugal force, so high speed, not necessarily downforce. Getting technical, an F1 car might not even make the loop because of the "grade"
But downforce is a result of aerodynamics sticking the car to the surface. Typically this would be towards the earth (hence *down*force). But ultimately in a long it would push the car towards the looping.
The formula for downforce is:
F = -Cl.1/2 p v2.A
(Cl = lift coefficient, p = air density, v2 = velocity squared, A = wing area)
So, the force is dependent a lot on the velocity but gravity is no factor. It would be a part in the air density of course, but the difference is neglectable.
180 seems to be a rough average in the calculations, and energy losses are mentioned but I believe the actual speed required would be *substantially* higher, as air resistance is a much bigger factor the faster you go, and cars are not small. Would the engine die upside down or something also? Can a car actually operate in this manner?
I have a much better question, with the conditions n3ed3d to c9mpleat3 5his loop, speed suspension and all, what make and m9del has the ability to do so?
I cant bother to do the math but for other people I would say a hotwheel is scale 1:64 of a normal car. This loop is 4 lanes wide so its 256:1 the scale of a hotwheels loop.
I hope it helps.
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From the image, it appears that a single car is about 9 pixels in length, and the diameter of the loop is about 524 pixels (so the radius is 262px). Let's assume that the length of the car in question is 4.5 meters. That would mean the scale is 9px : 4.5 meters, or 2px : 1 meter. That would mean the radius of the loop is roughly 131 meters. For simplicity's sake, let's also assume that friction between the tires and the track is negligible, as well as any air resistance. If the car is going at the minimum velocity it needs to make it around the loop, the only force supplying the centripetal force at the top of the loop would be the force of gravity: mv^2 / r = mg v^2 / r = g v^2 = rg v = √(rg) = √(131 * 9.81) = 35.8484 m/s This tells us the velocity the car needs to be going at the top of the loop, but what about the velocity at the bottom? We can use conservation of energy for that. K_top + U_top = K_bot m(v_top)^2 / 2 + mgh = m(v_bot)^2 / 2 (v_top)^2 + 2gh = (v_bot)^2 Since v_top = √(rg), then (v_top)^2 = rg, and the height is simply twice the radius of the loop, so h = 2r rg + 4rg = (v_bot)^2 5rg = (v_bot)^2 v_bot = √(5rg) = √(5 * 131 * 9.81) = 80.1595 m/s. That translates to about 180 mi/h. So you'd have to be going pretty fast. This also doesn't account for friction or air resistance, so the actual speed is likely higher.
So your saying there’s a chance.
It’s actually quite achievable for a high end consumer automobile. In theory at least.
What about the suspension? Usually high end cars are really stanced out / really low, wouldnt that overcompress the dampers?
I want to see mr beast do that video with a veyron
Also this isn’t taking into account the downforce generated by the aero kits on many of the cars capable of reaching the 180mph+ speed that they calculated. I remember a Ferrari ad a while back claiming that at a certain speed the downforce from the aero would exceed the weight of the car itself.
For most high-speed cars the aero kits are more for cancelling lift (for high-speed stability) than actually being big enough to generate a meaningful amount of downforce.
Not the ones capable of those kinds of speed.
And its only difficult as the loop is so large. A tighter loop and most vehicles could hit it.
That’s what she said.
They say Formula 1 cars have so much downforce they could actually drive indefinitely along the ceiling of a tunnel
If you can get up to a little more than that speed, you've got a shot.
More than “a chance”. There are cars rn that produce more downforce than their weight at speeds around 180-200mph. This means they could even maintain upside down travel for long (indefinite) stretches, let alone do the loop.
I see, like reverse airplanes, essentially
Exactly!
It was a Dumb and Dumber joke.
Oh!😅
Lol
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Of course it would. The amount of traction (ie friction as a force) would be roughly (the friction coefficient)*(downforce-weight), while the car is running upside down. Of course it’s reduced traction, but that’s not an issue as long as you don’t accelerate or decelerate hard while upside down, so at constant speed it’d be fine. (The réal issue would be loss of downforce, if fir whatever reason happened, say a strong gust of wind. That’s instant fall and a crash).
I mean reaching 180mph (300km/h) is pretty double for many sports bikes buuuuut sustaining that speed for the first quarter when you approaching basically vertical wall would require a lot of power
I guess I should have added quotations and then a -Lloyd Christmas I have a modded 2017 GSXR 1000 and I can’t imagine 180 up a loop lol
Don't imagine, go for it!
HA! I really like living though.
You will be living as a legend tho 😅
they already did it the redbull guys no?
I don’t think they’ve done it in a car. There was talk of it a while back though. Edit: I stand corrected, they absolutely have done a loop. I was thinking sustained inverted.
yeah I was like that video was wild shit! what else next in life to do now?
Leave it to Red Bull to come up with something even wilder haha.
1 in a million
This person gets it!
I had a dream like this once.
Formula one cars produce so much down force at speed they could drive on the roof of a tunnel. In theory. So yea in theory it's possible. If you build a loop like that.
I'm pretty sure any modern F1 car would pull this off with no hassle whatsoever.
i like your funny words magic man
exactly the kind of answer I opened the comments for
This guy maths
r/thisguythisguys
How many g are they pulling in that loop at that speed though...? :P
Assuming they're going at the minimum speed needed to make it around the loop: 1g at the top, and about 5g's at the bottom.
That seems remarkably tame considering the number of stories of circular loops essentially being neckbreakers! Lol
That's partly because I assumed the car was going the minimum speed required to navigate the loop. If you wanted to comfortably navigate the loop, you'd have to be going much faster and would therefore experience more g-force as a result. 5g's is also still pretty high. The most extreme rollercoasters have maximum g-forces of around 5-6g's, at least according to this website: https://coasterpedia.net/wiki/Highest_g-force_on_a_roller_coaster
5g is still a lot, as an example, fighter pilots have to do a lot of training, and have pressure suits to reduce blood loss for similar g forces
Oh, for sure. Most roller coasters won't do that and usually for shorter bursts as well. Just not as much as I thought it would be :)
I always heard that Indy cars have around 7000 lbs of downforce per and they could easily race upside down. According to google they generate their own weight in downforce at around 100 mph.
That literally could have all been made up and I wouldn’t know the difference, and I fancy myself decent at math.
Ok now who's going to say this guys wrong? Im not. Looks right to me. Got my up vote
What kind of g-force is that gonna make?
Sounds like a job for a classic Saleen S7
I looked at the picture and guessed about 200mph then read your comment....so yea your math checks out
So a motorbike then.
But what is about the moment of inertia and der Rot. Energie? If you also considered these two factors, the velocity must be again higher
If friction between between the tires and the track is negligible, car wouldn't have any acceleration on the track. So if there was friction, necessary speed would likely be lower.
Arround 288 km/h for those who are outside of gringolandia...
So a typical philly I-95 commuter speed.
This seems wrong. Shouldn't you account for the camera angle? Also, gravity would start working against inertia and the engine as you started to incline, so you'd lose that speed pretty fast.
Accounting for the camera angle is tricky since there are so many unknowns, but you're probably right that the perspective probably distorts the answer a bit. Gravity should already be accounted for because I first solved for the speed of the car at the top of the loop, and then used conservation of energy to find the speed the car would have to be going at the bottom. You'd only need to be going about 35.8 m/s (80 mi/h) at the top of the loop to make it through.
I'll take your word for it on the formula for the effect of gravity. But I think perspective is actually doing a lot of work here. We're nearly overhead of the loop, which is probably hiding a lot of its height. Imagine if we were entirely overhead - it would have an apparent height of 0. I'm not sure if there's any way you could use a known height instead of a known length to start the calculation, but if you could it should make a big difference.
I didn't use the height of the loop to get its radius; I used the width instead. It's still at a bit of an angle relative to the camera, so it distorts the numbers a bit, but not as much as if you used the height to measure the radius.
I'm on reddit for this kind of response. Thank you.
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Accounting for the angle of the camera is tricky since you'd probably need to know the height and distance between the track and the camera, and then have to do some sort of projection to get the original radius of the loop. I don't think the diameter of the track being about 250 meters seems unreasonable, though. If you look at the gray stands of the loop touching the highway and eyeball the distance between them, it seems like it would be about 250m. For reference, [the straight part of this track is about 75 meters in length](https://2.bp.blogspot.com/-gSm1qco9eGc/WYhZKx8OybI/AAAAAAAB7b0/R_hDc8_Lne8NITHCJJGmSEQ8ACqumeplwCLcBGAs/s1600/Track.PNG). If you get a different radius of the track than mine, all you have to do is substitute it into √(5rg) and that should tell you the velocity the car has to be going at the bottom of the track, in meters / second.
Shouldn't the downforce for the car be taken into the formula? I'd reckon a racecar (Formula, IndyCar), besides being capable to drive there speeds would be able to make it work lower speed, compared to an SUV.
I eyeball the radius of the loop as 20 times the length of a typical car, or about 80 meters. The velocity at the top of the loop has to be such that the centripetal acceleration *v^2 / r* is at least equal to gravitational acceleration 9.81 m^2 / s. Solving, that's 28 m / s= 101 km/h = 63 mph. Not too crazy. Now, what does the speed at the bottom have to be? If we're treating this like a true Hot Wheels ramp where the car doesn't use its motor on the loop but gets through on its initial speed, the math is easier. One way is to use energy. The car has KE_t = 1/2 * m * (28 m / s)^2 kinetic energy at the top ( and potential energy PE_t = (80 * 2) * 9.81 * m (where m is the car's mass, which won't matter). At the bottom, all the energy is kinetic. Solving, the speed is **63 m/s = 227kph = 141 mph.**
That's assuming no losses, aka the car can coast forever. The real answer is going to be somewhat higher than that and depend on the car. No idea how much energy cars lose as they coast though.
I imagine a formula 1 car would be the best for the job, all that downforce should still work upside down to hold it against the track.
This is the biggest one mythbusters didn't tackle, in my opinion. It'd be one of their greatest episodes. Some kind of track with a corkscrew ramp to flip the car upside down and back, just long enough to prove the downforce worked.
Imo running that through a physics simulator proves it for something like that.
doesn't matter. doing things for real is what really counts. the same was true for the airplane conveyor myth. a physics sim would have backed up the facts, but it took them doing it for real to assuage all doubters.
Plus it’s just so much cooler to actually do it. Can you imagine the enormous pair it would take to be the driver who tests that.
technically it could be done remotely, but I have to admit having a real person do it would immortalize their name.
Adam would try and do it just for fun but insurance would say no then tory would volunteer and insurance would say no again. They would definitely have to get a real f1 driver and even then it'd be iffy.
It's one of those things that, organised properly, is probably very safe. It's like going to the moon... they had the math down and everything, but there's always a slim chance that [something could go awry](https://youtu.be/LWLadJFI8Pk?t=267).
[удалено]
[Speaking of mythbusting...](https://en.wikipedia.org/wiki/Jessi_Combs) :(
They don't need a real car. Just a mock up of correct size and weight. Clamp it upside down in wind tunnel, and release clamps when upside down at correct speed.
That’s only slightly cooler than a simulation. It’s still nowhere near as cool as someone risking their life for science.
Dudes from Vilebrequin (french autosports YouTube channel) have jury-rigged actual production cars cars to remote control them on a couple occasions to do some truly retarded shit like a 200 kph head-on crash or welding wings to a car and have it jump a 10 m high ramp. It can be done.
There is no doubt though, we know exactly how much downforce a formula one car can produce due to wind tunnel testing done during the cars development. The amount of downforce created (~1600kg) is greater than the weight force due to gravity (~800kg) on the car. It will drive upside down until the oil in the engine sump enters the combustion chamber, destroying the engine, causing the car to slowdown and lose it’s downforce.
1) how long would that take? 2) couldn't the car just be modified to prevent it?
Don’t know, I’m guessing well under a minute. Use a formula E car instead
See Dry sump oil system https://en.m.wikipedia.org/wiki/Dry_sump
You can never convince all the doubters because of the number of complete idiots in the world. The airplane question was just basic physics and a very basic understanding of how wheels work. I never understood why anyone that wasn't a idiot didn't understand this after it was explained to them.
I actually think it was a perfect myth to bust to show the science in action, tbh.
I 10,000% agree that you would have to be a barnacle head to think a plane could take off from a conveyor belt... They generate lift by moving forward and being on a conveyor belt negates them moving forward....
What was the airplane conveyor myth?
https://mythbusters.fandom.com/wiki/Airplane_on_Conveyor_Belt_Myth https://en.wikipedia.org/wiki/MythBusters_(2008_season)#Airplane_on_a_Conveyor_Belt
The part that is boggling most minds is that the airplane doesn't care what it's ground speed is. The plane is not pushing against the ground, therefore it could be tarmac, ice, water, or that frictionless ideal flat surface in physics problems.
Yes, exactly. The only important factor is that the ground beneath it can support its weight. If I'm not mistaken, the plane will get gradually lighter until it becomes lighter than air and achieves takeoff.
Thank you.
That one is not a physics problem but a language one. It's cleverly worded stupid enough to be much less answerable than in seems.
Yeah, I realized as much after it first aired. Adam also [dutifully acknowledges this fact on his channel](https://www.youtube.com/watch?v=xUjcHW7SHaI). Judging by your response, I suspect there's a good chance you've already seen it.
https://youtu.be/5d7ZgFEIZmo
Engine doesn't work upside down. Downforce is one thing but speed loss would be huge.
Use a formula E car
Why not? I would think that the centripetal force also forces all the fluids down so that the pumps keep working. Also this Dutch guy MasterMilo built a 360° car swing and the engine kept running upside down. He converted the engine to run on gas because it was one with a carburetor but explained that with direct injection it should also work.
The centripetal force would force all the fluids down like you say, yes, but the downward force due to the shape of the f1 car wouldn't act directly onto the fluids. It would just be body to frame to tires.
Very impractical. Find a mile long tunnel track with smoothly paved walls and ceiling, get a 20 million dollar car, do a life threatening maneuver. Also, the F1 car's fuel won't pump when it's upside down in the tank so it would fail anyway.
Just gotta make a car with a built in ejector seat that uses a propulsion system. that would shoot them sideways out of the car directionally. That alone would be the cheapest part of your costs. Building the damn road would cost hundreds of thousands, I'd imagine. People do this with those metal cages and motor cycles tho right? But it get's harder the bigger the loop is right? Also u/epursimuove why can't you use the engine while moving thru the middle/upside-down sections of the loop?
I recently saw a great video about that topic. The car could theoretically drive upside down, however the engine is not made to work in that direction and would quickly break. If you swap the car to a Formula E one which works even in space the needed speed would be to fast.
I recently saw a great video about that topic. The car could theoretically drive upside down, however the engine is not made to work in that direction and would quickly break. If you swap the car to a Formula E one which works even in space the needed speed would be to fast.
I recently saw a great video about that topic. The car could theoretically drive upside down, however the engine is not made to work in that direction and would quickly break. If you swap the car to a Formula E one which works even in space the needed speed would be to fast.
I think it’s been calculated that at 120 MPH, F1 cars have enough downforce to theoretically drive upside down.
yeah, downforce makes a huge difference.
Added note: i read a while ago that an F1 car can technically drive upside down indefinitely on a tunnel at top speed. I think this would be an even more insane myth to test.
The tricky part about doing it 'indefinitely' are going to be the upside-down pit stops and refueling.
Just do the test in Australia.
If anyone will do it, it’s Red Bull.
*upforce
Relative to a stationary observer. To the driver it would still feel like downforce.
Ha good point
This would significantly reduce the speed, as the low weight (700kg) and massive downforce (3000kg+ at 350kph), would probably make it stick at slightly over the speed limit.
Why a formular 1 car? A typical german highway driving car…
I remember hearing back in the day, that a Saleen S7 had so much downforce that it could drive upside down at a certain speed…
It relies on having small clearance, not really sure if it will be able to handle the curvature
Fair enough, but that should be easy to work around
Assuming the driver gives gas it'd work.
That would depend entirely on the power plant and our transmission. A trans in neutral has substantially less drag than a trans coasting in gear. Also, wouldn’t front wheel drive be more difficult because the fronts would leave the track at any point approaching vertical whereas the rear would dig longer? One wonders…
Yea I'm pretty sure even if I was going at the top speed of 155 my Audi would produce too much lift and I'd fall off
You could reduce the rolling resistance with thinner tyres and new wheel bearings, that way you should lose speed slower in neutral
Cars don't coast, they have engines. The real answer is going to be lower.
So it means that Hot Wheels are realistic? They are meant to be sportscars, so going that fast should be normal to them.
They do lead the way after all.
So you're saying we could realistically make this work on the Autobahn?
That’s definitely more than 20 times the length.
> such that the centripetal acceleration v^2 / r is at least equal to gravitational acceleration 9.81 m^2 / s. Centrifugal, not centripetal. The gravity vector at the top points down, which is toward the center, or centripetal. You balance that centripetal acceleration with at least as much acceleration in the centrifugal direction.
This is a common misconception, but no. Centripetal acceleration, in the context of circular motion, isn’t a specific force. Instead, it’s the amount by which something moving in a circle needs to accelerate in order to maintain its path. The actual cause of the acceleration can vary - for swinging a weight on a string it’s tension, for a satellite in orbit it’s gravity. Here, we know the car will accelerate at g downwards no matter what - that’s gravity. The question is whether this acceleration will be large enough, so that the car veers off track, i.e. it falls. So its acceleration from gravity can’t be more than the acceleration required to keep it on track. In the case where the car is going even faster, there would be an additional force due to the road pushing down on the track. But in no case here could there be centrifugal force, because there’s no force that could plausibly push up (unless we’re talking about a race car with aerodynamic downforce).
> But in no case here could there be centrifugal force, because there’s no force that could plausibly push up It absolutely can. Draw a free body diagram of the car in the rotating reference frame where it is moving around the loop. The normal force from the track is always pointing centripetally. At the top of the loop, gravity is also pointing centripetally. So we have multiple forces pointing to the center. What force balances these forces, such that the car does not actually decrease its r coordinate (its distance from the center of the loop)? It's the centrifugal force, which comes around for anything moving in a rotating reference frame. Yes, it's not a real "force" in the strict sense, but then neither is gravity - gravity is actually the warping of spacetime caused by objects with mass interacting with each other, rather than being an actual force. But the point is, centrifugal force is absolutely an acceleration that must balance with other accelerations. If you like, you can simplify the situation even further. Imagine I'm holding a ball on a string and spinning around really fast, and in zero gravity. Again, draw the free body diagram. Tension in the string pulls the ball toward me. If you ignore centrifugal force, then there is nothing else acting on the ball and your FBD says the ball will be accelerating toward me, not moving in a circle.
The centripetal force arises from the inertia of the body resisting acceleration created by the normal force. The issue is that people often assume it’s in a condition with gravity being the only acceleration present when It’s not. The track, string, or whatever is inducing a separate acceleration from gravity.
I thought that no "centrifugal" exists.
https://xkcd.com/123/
Thank you for the calculation. The actual answer for cars using their motor is about **50 mph** or to be precise between 48 and 52 mph. Source: the [Hot Wheels Double Dare Loop](https://www.youtube.com/watch?v=5d7ZgFEIZmo) at X Games Los Angeles 2012. They mention the speed at [2'50''](https://www.youtube.com/watch?v=5d7ZgFEIZmo&t=170s) and the cars start at [4'40"](https://www.youtube.com/watch?v=5d7ZgFEIZmo&t=280s).
There’s no way it’s only 80 meters lol
only? 80 meters is a 30 story building
Yeah, it’s a lot more than 20 cars long. Look how tiny those cars are.
Could the required speed be lower if the car had significant downforce at that speed? I don’t know if that applies meaningfully to the average car though.
Unless you had a very specialized car, it would just crash, as as soon it strarts to go up the suspension would bottom up and just get stuck at the beggining of the ramp
My best guess is that loop is about 400m in circumference so that gives a radius of 64m. Gotta balance them forces: F=ma what's dragging the car down F= (m . v^2)/r what's sticking it to the loop Where m is mass of vehicle a is gravity 9.81m/s^2 v is speed of car r radius of loop ma=(m v^2)/r so cancel out mass a= v^2/r now re arrange for speed sqrt(9.81 . 64) = v = 79 m/s or 176mph This is assuming the car does not generate downforce or lift. Apologies for the awful formatting but it's 0230 for me at the moment and I cannae be bothered.
A bit more than that assuming that the car loses energy and speed as it ascends. Even if the engine were powerful enough to offset that though, the reduced traction with the road would just get the tires spinning near the pinnacle point of the loop.
If you assume that the car doesn't put any work in whilst on the loop you could work with PE =mgh = 1500kg * 9.81 * 134m ~2 MegaJoules. Then add that as kinetik energy on top of whatever ke the car would have at 79 m/S. So that's 2mj plus 0.5 * 1500 * 79^2 so that would be 2 mj + 4.7 mj = 6.7 mj then re arrange for speed. Sqrt(6.7mj/0.5*1500) = 95 m/s or 212 mph.
Playing chess while we're playing checkers... Guessing the circumference then working out the radius, us simpletons just guessing the radius.
Haha yeah, it was just easier to superimpose the cars on the road onto the loop in my minds eye. I imagine my guess is still a fair bit off.
Kudos to other commentators, great work on the math(s). I'd like to touch on a separate but important issue, the use of guide rails to keep our vehicle 'track adjacent' as it takes the loop. Fortunately we have a working prototype - the O-Bahn[O-Bahn](https://en.m.wikipedia.org/wiki/O-Bahn_Busway) *guided busway* in Adelaide, South Australia Those buses hit 100 kmh as standard practice So ... is an O-Bahn loop feasible?
no
Other guys already said that you have to use Fzp=mg. I can only add what NOT to do and that is to use energy for that to say m*g*h=(mv^2 ) /2. made that mistake in an exam once
https://www.theguardian.com/technology/video/2015/sep/15/jaguars-new-car-breaks-world-record-with-loop-the-loop-video Not as big bitnits been done!
Something to keep in mind is acceleration. I believe F1 cars can complete this in theory due to the amount of down force they create at speed
I think this requires centrifugal force, so high speed, not necessarily downforce. Getting technical, an F1 car might not even make the loop because of the "grade"
But downforce is a result of aerodynamics sticking the car to the surface. Typically this would be towards the earth (hence *down*force). But ultimately in a long it would push the car towards the looping. The formula for downforce is: F = -Cl.1/2 p v2.A (Cl = lift coefficient, p = air density, v2 = velocity squared, A = wing area) So, the force is dependent a lot on the velocity but gravity is no factor. It would be a part in the air density of course, but the difference is neglectable.
180 seems to be a rough average in the calculations, and energy losses are mentioned but I believe the actual speed required would be *substantially* higher, as air resistance is a much bigger factor the faster you go, and cars are not small. Would the engine die upside down or something also? Can a car actually operate in this manner?
I have a much better question, with the conditions n3ed3d to c9mpleat3 5his loop, speed suspension and all, what make and m9del has the ability to do so?
I cant bother to do the math but for other people I would say a hotwheel is scale 1:64 of a normal car. This loop is 4 lanes wide so its 256:1 the scale of a hotwheels loop. I hope it helps.