Open The Ramp simulation on Moodle and familiarize yourself with its interface.
ID: 1965258 • Letter: O
Question
Open The Ramp simulation on Moodle and familiarize yourself with its interface. In particular, notice that you can make the person push the object up the ramp or down the ramp, and you can see a free body diagram of the object. Once you are familiar with the interface set the ramp to a fairly low angle (say 10?) and make sure you’ve chosen an object that is reasonably heavy and has reasonably high coefficients of friction.
(1) When the person pushes up the ramp with a small force (not enough to set the object in motion) what happens to the frictional force?
(2) Set the object in motion and play around with having the person push in various ways. Can you create a situation in which the person is pushing up the ramp and the force of kinetic friction also points up the ramp? If so, how? If not, why not?
Explanation / Answer
The frictional force helps the person keep the object from slipping down ramp if the person's force is less than the component of the weight that is pushing the weight down the slope. We can make the frictional force zero by pushing with a force equal to the component of the weight that is pushing the object down the ramp. If we push with a little larger force than the downhill component of the weight, then the frictional force is helping gravity. In other words, we can make the frictional force point up, down, or be zero. 2) kinetic friction always points away from the direction of motion. If we have a steep ramp and the person is pushing up with a small force, the object will be sliding down against the force of the person and against the force of kinetic friction.
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