## Finding the Friction Force on a Trolley Moving Down a Slope

Apparatus:

Dynamics trolley, runway, clamp stand etc., 2 x metre rulers, top-pan balance, set-square & stop-clock.

Diagram:

Procedure:

1. Clamp the runway in such a way that the dynamics trolley takes time,to roll, from rest, distancedown the runway.

2. Measure this time,three times. Calculate the average value of t.

3. In order to determine the angle of slope of the runwaymeasure heightand length Lengthshould be at least 70 cm. Calculate

4. Calculate the accelerationf the trolley by using

(If the trolley starts from rest, then).

5. Repeat for four more different angleswith the timevarying between about 1 and 5 seconds.

6. Tabulate your results.

7. Measure the mass M of the dynamics trolley.

8. Plot a graph of acceleration a (in m/s ^{2 }) against

Ensure that your acceleration scale goes down to at least minus 0.2 m/s ^{2 }.

Draw a best fit curve. Your graph should gently curve with a negative intercept on the acceleration axis.

9. Use your graph to find the angleof the runway when it is "frictionless" (i.e. when the acceleration of the trolley would be zero).

10. Draw a tangent to your line at the point where the acceleration is zero. Calculate the gradient of this tangent.

11. Record the value of the intercepton the acceleration axis.

12. Calculate the frictional force,acting on the trolley at low accelerations given that:

13. Why is the above method of measuring anglebetter than using a protractor?