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 Swinging Pendulum (Mass)

 

PURPOSE

Construct a pendulum and determine whether the size or mass of the pendulum affect the number of swings of that pendulum in a given time.
 

PERFORMING THE EXPERIMENT

  1. Suspend the thread from the notch in the iron ring on the ring stand by hooking the hook in the notch over the ring.  Then suspend the smallest washer on the hook at the bottom end of the thread. 

  2. Ask your adult partner to hold the base of the ring stand firmly as you perform the experiment.

  3. Pull the washer and thread forming your pendulum out to about a 45o angle.  Ask your adult partner to tell you when the second hand of the watch or clock reaches the minute mark.  Release the washer exactly at that time.  Caution:  Do not push the pendulum; simply release it.  Both of you should then count the number of swings back and forth until exactly 30 seconds have passed.  Back and forth count as separate swings.  Do not lose count!

  4. On the data sheet nearby, write your first and last name neatly, the number on the washer as an indication of its size and mass, and the number of swings that you observed in 30 seconds.

  5. Then repeat the experiment for three or four more washers of different size and mass, and record your additional results under the first set.  Do you observe any pattern in your data?
     

QUESTIONS TO THINK ABOUT

1. What force pulling on the washer caused it to fall when you released the pendulum?  Did the speed at which the pendulum moved differ during its swing?  At what point was it moving fastest?  At what point was it moving slowest?

2. Were your numbers of swings in 30 seconds for differing sizes and masses the same or different?  Do you know why that behavior was observed?  How could you perform this same experiment using equipment on a playground?

3. What experiment could you perform to determine whether the starting distance at which you released the pendulum changed the number of swings in 30 seconds?  Try it!  What do you observe?
 

EXPLANATION

The force of gravity caused the washer to fall and the pendulum to swing when you released it.  The speed of the pendulum increased as the pendulum approached the vertical position and decreased as it moved upward where it stopped.  The downward pull of gravity is the same on all substances regardless of their size or mass.  Therefore, the number of swings is the same for a washer of any size or mass.
 

EQUIPMENT NEEDED

Ring stands and iron rings; approximately 50-centimeter (20-inch) threads with ornament hooks at each end; 4 or 5 metal washers of differing sizes and masses; watch with second hand or a clock in the room with second hand.
 

REFERENCE

Modified from Janice Pratt VanCleave, Physics for Every Kid: 101 Easy Experiments in Motion, Heat, Light, Machines, and Sound, Wiley, New York, NY, 1991, page 74.
 
 


SWINGING PENDULUM (Mass) Data Sheet




First and Last Name       Number             Number             First and Last Name      Number               Number
                                   of Swings         on Washer                                              of Swings            on Washer

 

 
 
  
Kids Involved Doing Science is at http://www.kids.union.edu.
Modified 02/22/2001 by C. & P. Scaife