Thread: is it just Physics??

I was stuck trying to work out how they got the car in the truck with the door open. Then when they unload it the door's closed and there wasn't enough room to do that

Wonder if Mythbusters will try and replicate it.

Assuming the tunnel has been made circular at the entrance and exit of the stunt and that the tunnel has a diameter of 8m, it is possible. To do this the maneuver would have to be completed in less than 4 seconds to give a tangental speed around the tunnel of 6.26 metres per second. Looking at the video, it appears to complete it in around 4 seconds. At this speed, the car is weightless momentarily at the top of the loop.

Having said that, I doubt they would have done a stunt like that with people standing in the tunnel.


Jeremy's stunt shows it can be done, however the speed through the tunnel is irrelevant. The rotational speed (or tangental speed) is what is important.

plausible.
As long as the the G's are positive in relation to the surface its on then it'll stay stuck. Since the car had significant momentum/force in a direction intersecting the surface of the wall then it would have worked.
Theoretically if you could push a Defender hard enough all the way through and took the same line as the car, it'd work... And if it didn't have any suspension rebound

Try it with a marble in a cardboard tube or a soccerball in a sewer.

The car was only weightless to those standing on the ground, not the bloke in the car.


Its all relative

Originally Posted by longing4alandy

The car was only weightless to those standing on the ground, not the bloke in the car.

No, the driver would also be weightless as he is experiencing the same motion as the vehicle. Not really anything to do with relative position.

Paul,
The bloke in the car and the car are in the same frame of reference, so yes, whatever one experiences, so does the other. The crew on the ground are in a different frame of reference, so they don't experience things the same as the car/driver combo.
The car is always acted on here by a force, at first by gravity whilst on the road, then that is overtaken by centripetal force holding it to the tunnel wall.
The car/driver combo feels the centripetal forces and gravity similarly, but the crew don't feel the centripetal forces, just gravity.
So to the crew on the ground, the car is weightless or of negative weight when it is not falling or firmly planted on the ground. But to the driver, the car still weighs a tonne, and he still weighs 70 odd kg on the scales he's sitting on.
[The car/driver will actually weigh more in his frame of reference since the centripetal force will be at least equal to if not greater than that of gravity (weight=mass*gravity or in this case weight=mass*force that overcomes gravity)]

Same effect on the concave parts of rollercoasters, nascar circuits, olympic toboggan runs etc where the vehicle is able to deviate from 'flat earth' but not fall back down.

Hope that makes sense

Mark,
I think you've confused weight with mass. The driver and car do not change mass; however, I have calculated that if the tangental speed around the tunnel is 6.26 metres per second then the centripetal acceleration at the top of the loop is entirely due to gravity and hence, the driver and car experience no weight. If the driver is sitting on scales, they will read zero at the top of the loop.

Originally Posted by awabbit6

Mark,
I think you've confused weight with mass. The driver and car do not change mass; however, I have calculated that if the tangental speed around the tunnel is 6.26 metres per second then the centripetal acceleration at the top of the loop is entirely due to gravity and hence, the driver and car experience no weight. If the driver is sitting on scales, they will read zero at the top of the loop.

hang on you lot,,,


and-


having NO calculations to fall back on---

isnt this vid about the theory that the downforce created by the cars aero is enough to hold it upside down??

downforce is still downforce regardless of which way the car facing,,,

So what i believe others are trying to say is that even with out any aerodynamic forces the car could momentarily drive up side down if is went around the tunnel fast enough. Which is "all" mercedes did. Motorbike guys do it all the time at the circus.
What they say about some cars, like F1 cars, is that the aerodynamic forces generated are so great that they are more than the cars own mass in downforce. So once it was on the roof it could stay there as long as it went fast enough. We won't worry about small technical things like if it would still have enough traction while up side down to keep driving itself forwards.