# Predict the motion of a block (with friction)

You have ALREADY done this experiment:

• set up a track on your table so that it is tilted at an angle of 27 degrees
• let a block slide 80 cm from rest

If there were no friction, what should the acceleration have been? What was the actual acceleration you measured?

Based on your measurements,

1. compute the force of friction on the block
2. determine the coefficient of kinetic friction between block and track

Fine. But ... is this correct?

One way to find out is to change the angle of the track and repeat the experiment. If friction really behaves as described in class and in your textbook, then NOW you should be able to predict the motion of the block accurately. Let's see if you can....

1. change the tilt of your track to 23 degrees
2. predict the time it should take for the block to slide 80 cm; be sure to include friction as necessary
3. write your calculations and prediction neatly on a piece of paper, and hand it to an instructor
Now let the block slide, and see if you were right!

If you have time ... Repeat the experiment at this same angle of 23 degrees, making at least five trials. What sort of uncertainty should you attach to your measurement of acceleration? What sort of uncertainty should you attach to your measurement of coefficient of kinetic friction?