# Roller Coaster Physics Question

Wednesday, March 5, 2003 10:28 AM
When I was a ride op and was driving the ride, the PLC would display the speeds of the trains. The empty train would consistantly have a slower speed at certain points along the course than a full train. Theoretically this does not make physical sense but I always thought that the smaller train might be affected more by the external outside forces such as wheel and wind friction. Thus the train with the lighter mass would have a smaller magnitude of acceleration and would have a smaller final velocity at the bottom. Is this correct explanation for why the empty train is slower. Any one who could give a good technical explanation for this and perhaps correct my explanation feel free to respond to this post
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Wednesday, March 5, 2003 10:45 AM
I think a fully loaded train would have more momentum.
Top speed would be the same but a 2 ton train would be harder to stop or slow down than a 1 ton train.
Like when you go bowling and one person uses a 16 lbs ball and another uses an 8 lbs ball. Roll both at the same speed and see how the 16 pounder knocks the pins around harder then the 8 pounder as the 16er has more momentum(I believe that is the proper term for it).

Jim Wolgamuth
OW op

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Wednesday, March 5, 2003 1:22 PM
I understand what your saying and kind of agrees with what I said above. Momentum is equal to the velocity multiplied by the mass of an object. So the full train has larger mass and thus greater momentum. So a full train because of its greater momentum should be less effected by outside forces such as wheel or wind friction. However you said that the top speed would be the same for both a full train and an empty train. This is only true if there is no friction, which is not a realistic situation. The full train would have greater top speed, and this was observed by looking at the PLC and comparing the speed at the bottom of the hill for a full train and an empty train. The longer the course the greater the difference between the speed of the top speed and the final speed. For example the speed at the midcourse of the coaster for a full train would typically be around 6 to 8 miles per hour faster than the empty train. The forces our a function of the velocity and the radius of curvature. So Obviously this would effect the forces and the quality of the ride experience.
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Wednesday, March 5, 2003 1:49 PM
You answered your own question, Dave. The increased momentum of a loaded train will overcome friction with a greater resultant force, resulting in higher speeds throughout the course.

As far as wind resistance goes, think of it as a collision...a Mack truck slamming into a VW beetle will slow down a LOT less than, say, a Civic would.
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digi
"There's always room for SFWoA!"

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Wednesday, March 5, 2003 2:31 PM
In terms of physics. the heavier the train is at the top of the first hill, the more potential energy is available. If there was no friction or if all frictional forces were a direct function of weight, trains would travel at the same speed regardless of weight. However, many frictional forces such as aerodynamic drag, and lubricant drag in the bearings are not a function of weight. They are nearly constant regardless of weight. This results in a lighter train with less energy available being slowed more than a heavier train.
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Wednesday, March 5, 2003 5:24 PM
I think I understand what your saying about friction and frictional forces affecting the lighter train more therefore its top speed would be lower. I thought David was saying the the top speed was the same put the the average speed was not. Makes sense to me now; thanks for the education David & digi.

Jim Wolgamuth

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Wednesday, March 5, 2003 5:29 PM
Reminds me of physics with the greatest examples ever. Momentum:

A dump truck hitting a cheerleader.... dump truck wins and doesn't even slow down.

A bicycle hitting a cheerleader.... bike will slow down significantly and cheerleader will start moving.

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Chris Tyson
Photographer
www.pkiunlimited.com

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