# Movie Physics speed

1. Oct 5, 2008

### chris123

Movie Physics "speed"

1. The problem statement, all variables and given/known data
In the 1994 movie "speed" the bus takes a 90 degree corner at an estimated speed of 81kph. in reality would the bus turn the corner safely or roll due to torque? (disregard the movement of people to one side of the bus.)

"m" of bus=6000kg
coeficient of friction tyres to road=0.9=u
"V" of bus=81kph=22.5ms/s/
"r"=15m
"g"=9.8
2. Relevant equations
Fcp=mv^2/r
Ff=mug
"T"torque=Fxr
3. The attempt at a solution
Fcp=mv^2/r=6000x22.5^2/15=202500
???

2. Oct 5, 2008

### LowlyPion

Re: Movie Physics "speed"

Welcome to PF.

How much frictional force does the bus make with the ground?
You've calculated the radial force OK.

3. Oct 6, 2008

### chris123

Re: Movie Physics "speed"

Ff=ugm=0.9x22.5x6000=121500

hows that???

just need help with steps cheers,,,,

4. Oct 6, 2008

### chris123

Re: Movie Physics "speed"

TORQUE

T=Fxr=1822500

soo how do i know if this alright or if it flips???

5. Oct 6, 2008

### LowlyPion

Re: Movie Physics "speed"

The radial Force is not exactly the torque. Surely it will contribute to it.

The torque would be a moment about some pivot point, presumably the outer wheels if it was to flip on the turn.

Without further knowledge of the geometry of the bus, (its center of mass relative to the wheels) I'd think the only thing that would happen is that it would be sure to skid, because the frictional force is insufficient to maintain contact with the road.

6. Oct 7, 2008

### chris123

Re: Movie Physics "speed"

Length=12 metres height=3 metres width=2 metres

??? does this help

7. Oct 7, 2008

### LowlyPion

Re: Movie Physics "speed"

If the frictional force is exceeded, then the bus should slide. Hence the force available to pivot about the outer wheel is going to be given by the force from friction. The forces then that balance the torque are the downward force of the weight through the center of mass times it's distance from the wheels compared to the frictional force times the height above the wheel. (Draw a diagram to satisfy yourself.)

If Friction Force X 1/2 height is greater than weight times 1/2 width then it will tip. Once tipped it should continue because the moment arm of the lateral force increases and the distance of the weight through the center of mass will move closer to the outside wheel.