The force pointing out involved in a buss-turn.

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In summary, the conversation discusses the movie Speed and a scene where a bus flips due to a 90 degree turn. The calculations for finding the maximum velocity through the turn are explained, with a torque due to gravity and a torque due to centripetal force being the determining factors for the bus flipping. The concept of centripetal force is also explained, with it being the inward component of tension or friction and not a separate force. The conversation concludes by suggesting the use of a rotating frame to solve the problem.
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jegerjon
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Hi guys,

I have been reading on the board for a while, and I have been enjoying the information that i have gathered. Now I have a question for you, though.

Have any of you seen the movie speed? In this movie they do a 90degree turn, and the buss flips due to the torque. They also tested this in mythbusters, I believe.

I have been thinking about the calculations in order to find the maximum velocity through the turn, and they seem pretty straight forward. We have a torque due to the gravity (attacking the COM), and a torque due to the centripetal force (also attacking the COM). Both torques with respect to some axis at the outer wheels. When the torque from the centripetal force becomes larger than the torque from gravity, the buss will flip.

These calculations seem to work, but HOW can I explain the part with the centripetal force? Because, it can not be the actually centripetal force, since this point inward and the buss obviously tilt the other way. Can this be explained with the centrifugal force? If so, how exactly, and also, why doesn't the real centripetal force not give a torque pointing inward the circle? Is this because the centripetal force is really just the frictional force between tire and road, and that this force does not attack in the COM?

Thank you in advance :)
 
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welcome to pf!

hi jegerjon! welcome to pf! :smile:

centripetal force is not a separate force

it is only an alternative name for the radially inward component of tension or friction or other force or forces on a body

in the case of the bus, it is the friction force, which of course is irrelevant to tipping, since it has no torque about the tipping axis

the easiest way to solve this is to use the rotating frame of the bus …

in that frame, there are two relevant forces, mg vertically downward, and the centrifugal force mv2/r horizontally outward :wink:
 

1. What is the force pointing out involved in a buss-turn?

The force pointing out involved in a buss-turn is known as centrifugal force. It is the outward force that is experienced by an object moving in a circular path.

2. How is centrifugal force different from centripetal force?

While centrifugal force pulls an object away from the center of rotation, centripetal force pulls an object towards the center of rotation. These two forces are equal in magnitude and opposite in direction, and together they keep an object moving in a circular path.

3. What factors affect the strength of centrifugal force?

The strength of centrifugal force depends on three factors: the mass of the object, the speed at which it is moving, and the radius of the circular path it is following. The greater the mass or speed, or the smaller the radius, the stronger the centrifugal force will be.

4. Is centrifugal force a real force?

No, centrifugal force is not a real force. It is an apparent or fictitious force that arises from our frame of reference as observers in a non-inertial reference frame. It is a result of our tendency to perceive motion in a straight line rather than a curved path.

5. How does centrifugal force affect objects inside a bus during a turn?

Centrifugal force will cause the objects inside the bus to feel as though they are being pushed towards the outside of the turn. This is why it is important for passengers to hold onto something during a turn to prevent them from sliding or falling. The force is also responsible for the feeling of being "pressed" against the seat during a sharp turn.

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