Circular Motion Activity

Apparatus:

Glass rod, fire polished at both ends
Hooked masses
Triple-beam balance / 2m polyester thread
meter stick
steal ball with hole

Procedure:

  1. Securely tie the string to the steal ball. Thread the other end of the string through the glass rod and tie it securely to another mass about three times as heavy – use one of the hooked masses. Record both masses.
  1. Using the center of the small mass as the zero point, mark the string at intervals of 15 cm, be sure to make dark marks that are easily seen.
  1. Holding the glass rod firmly, swing the smaller mass around in a circle until a stable orbit is achieved with the first 15cm mark sliding along the top edge of the glass tube. Keep the motion of the glass tube itself to a minimum. Have your partner time 20 complete revolutions with a stopwatch so that the period (T) can be accurately measured. If the mark on the thread moves away from the top edge of the glass then you will need to start again. The main purpose here is to record the period (T) and the length (L). So L must be kept very constant and T counted accurately.
  1. Repeat the procedure for the next 8 points along the thread. Make a table showing the period, T, and the length of the string, L.
  1. Plot the graph of T2 vs. L and draw a line of best fit.
  1. Find the slope of your graph. Do the calculation neatly on the graph itself.

Discussion and Conclusion:

Use all of the following in you discussion and conclusion. I do not want them answered as separate points. I want them all included in one or two well-structured paragraphs.

  1. Compare the graph that you drew in procedure step 5 to y = mx + b.

a) Include the theoretical slope?

b) Include is the actual slope?.

  1. Does your data support ? Explain.
  1. Include some sources of error.

Practice problems:

  1. A ball of mass 0.50 kg is swung in a circle of radius 2.0 m with a period of 1.5 s (as in figure # 028).

a)  What is the speed of the ball?

b)  What is the acceleration of the ball?

c)  What centripetal force must be exerted by the string in order to keep the ball in orbit?

d)  What is the mass of the central object?

e)  What angle does the string make with the vertical?

f)  How long is the string, L?

  1. A record of diameter 30 cm rotates on a turntable at 33.3 r/min.

a)  How fast is the outside edge of the record moving?

b)  How many times as fast would it move if the frequency were raised to 78 r/min?

  1. A satellite is kept in a circular orbit 300 km above the surface of the Earth by the force of gravity. At this altitude the acceleration due to gravity is only 8.9 m/s2. The radius of the Earth is 6.4 x 106m.

a)  calculate the period of the satellite.

b)  Calculate the speed of the satellite.

  1. Calculate the frequency with which the Earth would have to rotate so that an object on the surface of the Earth at the equator would just become “weightless.”

Tolksdorff Circular Motion Activity 1 of 2