# Car on a treadmill

1. Dec 30, 2007

### bunion

What would happen if you drove a car at 40mph along a road onto a giant car treadmill running at 40mph? Would you experience any noticeable g force shock? If the car was on the treadmill and the treadmill started slowing down what would happen to its speed when it left the treadmill and rejoined a road?

2. Dec 30, 2007

### Shooting Star

As soon as you are aboard the treadmill, you'll be moving at 80 mph wrt ground, because you still have your engines on at the same power. Then definitely there was accn and thus g forces during the time you crossed over.

If the treadmill starts to slow down, the car will also slow down and so again g forces. At the time of rejoining the road, the speed of the treadmill has not been specified. Assuming it's still moving, then the car will experience a braking force until it's going at 40 mph again, and thus again some g forces during the time until it has slowed down to 40 mph.

Whether all these g forces were "noticeable" or not depend on the times involved and will require more precise calculations with additional information

Last edited: Dec 30, 2007
3. Dec 30, 2007

### rcgldr

The car would transition onto the treadmill at 40mph relative to ground, 0mph relative to the treadmill, and the engine would most likely stop if the driver didn't use the clutch or shift into neutral as the car transitioned onto the tread mill. Once on the tread mill, the car could be accelerated as if it were moving at 0mph, since the point of application of force at the rear tires is now the treadmill.

4. Dec 30, 2007

### bunion

Sorry forgot to say the treadmill would be running in the opposite direction

5. Dec 30, 2007

### Staff: Mentor

If the treadmill were going in the opposite direction so the combined speed was 80 mph, the car's wheels would spin up to 80 mph almost instantly and the car would then decelerate slowly to just a few mph with respect to the ground and, say, 45 mph with respect to the treadmill (if the driver applied no extra gas).

6. Dec 30, 2007

### nacho-man

by reading all your posts i can see that you guys understand quite a bit about physics.
As i havent studied it before; but will soon, would u guys have any tips for me to get like an extra boost.. any easier way to understand physics?

7. Dec 30, 2007

### DaveC426913

Mythbusters dispelled (or confirmed, depending on your PoV) this myth on one ep. Pretty much, anyway.

They drove a car from highway speed onto a ramp behind a truck.

The wheels adjusted instantly, and there was almost no noticeable jerking in the car.

Of note: the engine did NOT die as soon as the wheels stopped. They were able to drive the car up the ramp into the truck.

8. Dec 30, 2007

### belliott4488

Cool! I've fantasized about doing this many times. I'll bet they were driving an auto. transmission car, though. With a stick shift, you'd have to do a quick downshift to accommodate the sudden decrease in wheel speed, wouldn't you? Of course, I drive a front wheel drive car - I guess it doesn't matter with RWD, does it?

9. Dec 31, 2007

### DaveC426913

I think they drove the same model from Night Rider - a 1982 Pontiac Firebird Trans Am.

10. Dec 31, 2007

### bunion

Thanks for the help everyone

11. Dec 31, 2007

### nacho-man

i needed help too..

12. Jan 28, 2008

### Bill Foster

If the car had wings would it take off?

13. Jan 28, 2008

### Staff: Mentor

No, it wouldn't. Cars can't fly.