Realistic Bus Cornering Speed: Physics Analysis of "Speed" Movie | 1994 Film

In summary, the movie "speed" shows a bus taking a 90 degree corner at an estimated speed of 81kph. In reality, the bus would not be able to turn the corner safely due to insufficient frictional force and would likely skid. However, if the bus were to exceed the frictional force, it could potentially tip over depending on its dimensions and center of mass.
  • #1
chris123
4
0
Movie Physics "speed"

Homework Statement


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

Homework Equations


Fcp=mv^2/r
Ff=mug
"T"torque=Fxr

The Attempt at a Solution


Fcp=mv^2/r=6000x22.5^2/15=202500
?
 
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  • #2


chris123 said:

Homework Statement


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

Homework Equations


Fcp=mv^2/r
Ff=mug
"T"torque=Fxr

The Attempt at a Solution


Fcp=mv^2/r=6000x22.5^2/15=202500
?

Welcome to PF.

How much frictional force does the bus make with the ground?
You've calculated the radial force OK.
 
  • #3


Ff=ugm=0.9x22.5x6000=121500

hows that?

just need help with steps cheers,,,,
 
  • #4


TORQUE

T=Fxr=1822500

soo how do i know if this alright or if it flips?
 
  • #5


chris123 said:
TORQUE

T=Fxr=1822500

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

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


LowlyPion said:
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.

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

? does this help
 
  • #7


chris123 said:
Length=12 metres height=3 metres width=2 metres

? does this help

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.
 

1. What is the realistic maximum speed for a bus to safely navigate a corner?

The realistic maximum speed for a bus to safely navigate a corner depends on a variety of factors such as the size and weight of the bus, road conditions, and the sharpness of the corner. In general, a bus should not exceed a speed of 10-15 mph when making a sharp turn, and should slow down even further for tighter turns.

2. How does the physics of a bus affect its cornering speed?

The physics of a bus, particularly its mass and center of gravity, play a significant role in determining its cornering speed. A bus has a high center of gravity and a large mass, making it more prone to tipping over while turning. Therefore, the bus must maintain a lower speed to counteract these forces and safely navigate a corner.

3. What are some common mistakes or unrealistic scenarios shown in the "Speed" movie's bus cornering scenes?

Some common mistakes or unrealistic scenarios shown in the "Speed" movie's bus cornering scenes include the bus making sharp turns at high speeds without losing control, the bus jumping over a large gap in the freeway, and the bus being able to maintain a constant speed while navigating multiple corners. These scenarios are highly improbable and would not be possible in real life.

4. How do road conditions affect a bus's cornering speed?

Road conditions, such as wet or icy surfaces, can greatly impact a bus's cornering speed. These conditions reduce the amount of friction between the tires and the road, making it more difficult for the bus to maintain control while turning. In these situations, the bus must slow down even further to safely navigate the corner.

5. Is it possible for a bus to completely lose control while making a turn?

Yes, it is possible for a bus to completely lose control while making a turn, especially if it is traveling at an excessive speed or if the road conditions are poor. In these situations, the bus may fishtail or spin out, which can result in a rollover or collision. This is why it is crucial for bus drivers to adhere to proper cornering speeds and drive cautiously in hazardous conditions.

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