Build and Use a Pendulum

Pendulums are a lot of fun and easy to make! A pendulum is basically an object that hangs down from a fixed point which swings backwards and forwards under the action of gravity. While pendulums can be used in clocks to help manage the clock hands, or to show the movement of the earth, they are also a great experiment!

Steps

Building a Pendulum

  1. Collect your materials. This pendulum experiment is easy to do at home. All the materials should be readily available. For the purposes of this article you'll only be doing one pendulum, but you can cut more of different lengths, so make sure that your length of string is over {{safesubst:#invoke:convert|convert}}.[1]
    • Gather two chairs and a meter stick. You'll use the chairs and meter stick to create the frame for your pendulum. The pendulum will hang off the meter stick between the chairs.
    • The scissors are for cutting the string and the tape if you need it. The tape is if you end up using pennies instead of washers.
    • Your string should be at least {{safesubst:#invoke:convert|convert}}, but preferably longer. It can be string or yarn, depending on what you have available.
    • The stopwatch will be for recording things like the period of the pendulum and how the period changes when you change the angle of the pendulum or the length.
    • You can use five washers, or three pennies to weight the pendulum. These are good weights to use and easy to find in your house.
  2. Put 2 chairs back to back. You will want them spaced about one meter apart, because you'll be placing the meter stick across the backs of them. Make sure that you're facing them back to back because otherwise the fronts will get in the way of the pendulum's arc.
    • Put the meter stick across the tops and make sure that it is centered between the backs of the two chairs. Off-centering the meter stick can make your calculations incorrect.
    • If the meter stick is sitting stably on the back of the two chairs, you can tape it down to keep it in place.
  3. Cut string to {{safesubst:#invoke:convert|convert}}. This is the string that will make up one part of the pendulum. All you'll need to do is add a weight. If you do choose to make more pendulums of varying lengths you'll find that frequency of the pendulum (how many times it swings backwards and forwards per second) is dependent on the length of the string.
    • Tie the string towards the middle of the meter stick. This will make it so that the pendulum won't hit the chairs.
  4. Tie 5 metal washers to the free end of the string. These are your weights, which will turn the pendulum into the pendulum. Instead of metal washers you can use three pennies. Tape them securely to the free end of the string.
    • You'll find that a pendulum with a heavy weight will move at the same rate as a pendulum with a light weight (like a foam ball from a fabric shop, for example) because with gravity the acceleration (speed) of a falling object is the same whether it is heavy or light.

Using the Pendulum

  1. Pull the string tight at an angle from meter stick. You'll do this by holding the weighted end of the strings, where the washers or pennies are. Depending on the angle, the frequency of the pendulum can change.
    • For example, releasing the pendulum from a 90 degree angle to the meter stick might give you a different frequency of motion than, say, a 45 degree angle.
  2. Let the pendulum go. Make sure that you're releasing it so that it won't hit anything during its swing. If it hits something you'll have to start over again. While you're letting the pendulum go, you're going to be timing its arc so be ready.
  3. Time its arc. Start timing the pendulum as soon as you release it. When the pendulum returns to its original position, stop timing. It can be helpful to have an assistant while you do this, so you can manage the pendulum while they manage the stopwatch.
    • The single arc that the pendulum makes is called the “period of the pendulum.” You can also find out the frequency by seeing how many times it swings back and forth per second.
  4. Release the pendulum again. Time it to find out if the pendulum makes the same time as it did the first release. Make sure that you're releasing from the same angle. Have you noticed any change?
  5. Record your observations. Make note of the times of the period of the pendulum and its frequency so that when you start doing creative things with your pendulum you can see how things change.
    • This will help you to understand the two major applications of pendulums. One is for time telling, the other is called the Foucault Pendulum. For the former, the motion of the pendulum governs the movement of the clock hands.
    • The Foucault Pendulum demonstrates the rotation of the earth. It has to be incredibly large (sometimes over two stories high) so that it will swing over a longer period of time.

Doing Creative Things with Your Pendulum

  1. Cut a second string. Using a second, or even third, string can help you demonstrate the special properties of the pendulum. Make the string shorter than your first one, or weight it differently.
    • Cut 2nd string to {{safesubst:#invoke:convert|convert}}, if you're testing how a difference in height works for pendulums.
    • Place the second string {{safesubst:#invoke:convert|convert}} from the first one, so they don't bump into one another during their rotations.
  2. Change the weight. Test pendulums of different weights and see if there is any change in their rotation and in their frequency. Time them to see what, if any difference, there is.[2]
    • Repeat several times (around five) and average out the times that you've recorded, or oscillations of the pendulum. This will give you the average movement of the pendulum.
  3. Change the angle. While a slight angle change tends not to have any effect on the rotation of the pendulum, you might try making a really big difference and see what that does. For example, placing one string at 30 degrees and one string at 90 degrees.[3]
    • Again, while you're testing out the different angles, you'll want to repeat the experiment around five times to get the best information.
  4. Change the length. Find out what happens with the speed of two different lengths of pendulum. Time them to see if the shorter pendulum is faster or if it remains the same as the longer one.
    • Repeat, repeat, repeat. Then average out the times and oscillations of the pendulum.

Tips

  • Don't use anything fragile or valuable as the mass. It might break.
  • Keep the string considerably longer than the diameter of the mass.

Warnings

  • Do not use any thing extremely heavy as the pendulum's weight; otherwise, the string may break.

Things You'll Need

  • Two chairs
  • Meter stick
  • String
  • Scissors
  • Stopwatch
  • Tape
  • Five washers (ten if you make two pendulums) or three pennies (six if you make two)

Related Articles

Sources and Citations

  1. ↑ http://www.scientificamerican.com/article/bring-science-home-swinging-pendulum/
  2. ↑ https://explorable.com/pendulum-experiment
  3. ↑ http://www.school-for-champions.com/science/pendulum.htm#.U77XKKjd1e4

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