The force pointing out involved in a buss-turn.

  • Thread starter Thread starter jegerjon
  • Start date Start date
  • Tags Tags
    Force
AI Thread Summary
The discussion centers on the physics of a bus flipping during a 90-degree turn, referencing the movie "Speed" and a Mythbusters episode. The calculations involve analyzing the torques from gravity and centripetal force acting on the center of mass (COM) of the bus. It is clarified that centripetal force is not a separate force but rather the inward component of other forces, such as friction, which does not contribute to tipping. The conversation suggests using a rotating frame of reference to better understand the forces at play, specifically the downward gravitational force and the outward centrifugal force. This approach helps explain the dynamics of the bus during the turn and the conditions leading to its potential flip.
jegerjon
Messages
1
Reaction score
0
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 :)
 
Last edited:
Physics news on Phys.org
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:
 
Thread 'Gauss' law seems to imply instantaneous electric field'

Thread 'Gauss' law seems to imply instantaneous electric field'

Imagine a charged sphere at the origin connected through an open switch to a vertical grounded wire. We wish to find an expression for the horizontal component of the electric field at a distance ##\mathbf{r}## from the sphere as it discharges. By using the Lorenz gauge condition: $$\nabla \cdot \mathbf{A} + \frac{1}{c^2}\frac{\partial \phi}{\partial t}=0\tag{1}$$ we find the following retarded solutions to the Maxwell equations If we assume that...
View full post »

Thread 'Highway: Deriving speed from Doppler shift'

I passed a motorcycle on the highway going the opposite direction. I know I was doing 125/km/h. I estimated that the frequency of his motor dropped by an entire octave, so that's a doubling of the wavelength. My intuition is telling me that's extremely unlikely. I can't actually calculate how fast he was going with just that information, can I? It seems to me, I have to know the absolute frequency of one of those tones, either shifted up or down or unshifted, yes? I tried to mimic the...
View full post »

Similar threads

I Origin of Centripetal force when the net force toward the center is 0?
Replies
8
Views
3K
I How to quantify gyroscopic precession torque?
Replies
34
Views
3K
I How is static friction the centripetal force during a car turning?
2
Replies
73
Views
9K
I Does Larmor precession change the force exerted on a magnetic dipole?
Replies
1
Views
1K
B Torque applied by a continuous mass instead of point particle
Replies
14
Views
2K
I Gravity machine force calculations assistance needed
Replies
13
Views
2K
I Finding the Axis of Rotation with Given CoG and Force Point
Replies
32
Views
2K
B Rolling Without Slipping on an Inclined Plane
Replies
5
Views
2K
Precession: A picture using only forces
Replies
2
Views
1K
I On whether the motion of a Foucault pendulum bob is comparable to ballistics
Replies
10
Views
2K

Hot Threads

Recent Insights

Back
Top