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Old Feb 2nd 2011, 01:25 PM   #1
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Post How does the mass of a trolley affect its acceleration going down a slope?

Hello all, I'm new here

I did an experiment in Physics class (I'm in high school, 10th grade) involving mass and acceleration. I took a trolley, let it roll down a ramp, and measured its acceleration. I changed the mass of the trolley on every trial and on every trial, measured its acceleration. My results were very puzzling.

F = ma suggests that if I increase the mass of an object, its acceleration will decrease. However, my results proved that with a higher mass, the acceleration remained constant. I didn't change the angle of the ramp or the distance it traveled. And the acceleration was measured with a computer, so the results are pretty precise.

So my question is, how did this happen? Shouldn't the acceleration have decreased as I made the trolley heavier?

Thanks a lot in advance!
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Old Feb 2nd 2011, 10:11 PM   #2
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Well, if you were in higher classes, you'll learn about components (not sure if you know about them because my education system is different)

I assume that you are familiar with variables and if you don't understand something, just say it.

Make a sketch of what is happening: the trolley on a slope at θ degrees with the horizontal.

The force acting on the trolley down the slope is given by:

F = mg sinθ

This is only the force. Now to compute the acceleration, you use F = ma.

So, we get:

ma = mg sinθ

Do you see what happens?

The acceleration of the trolley depends only on the inclination of the slope and the acceleration due to gravity.

a = g sinθ
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Old Feb 4th 2011, 03:14 PM   #3
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I'll add a quick note to Unknown008's reply. This effect is basically the same as for falling objects. The only force on an object in free-fall is the object's weight, so we have
(net)F = ma

w = ma

mg = ma

Thus the acceleration of an object in free-fall is a = g = constant for any object. The acceleration due to gravity does not depend on the mass of the object.

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