Name ______Block ______PSA 1.55 West Making a Clock

Question: How can you use a pendulum to measure time?

In this investigation, you will design a pendulum clock that can accurately measure on minute.

Pendulum clocks were once among the most common ways to keep time. It is still possible to find beautifully made pendulum clocks for sale today. To make a pendulum clock accurate, the period must be set so that a certain whole number of periods will equal one minute. For example, you could design a pendulum clock with a period of two seconds. Then, thirty periods of the pendulum would equal on minute. A pendulum clock has a gear mechanism that turns the hands a certain distance for each swing of the pendulum.

You have probably noticed as you have worked with pendulums that the amplitude gets smaller over time. Like all moving systems, pendulums lose energy due to friction. Real pendulum clocks have weights that slowly fall down. The weights give up their potential energy to keep the pendulum swinging (kinetic energy) at a constant amplitude. The weights have to be lifted every few days. Otherwise, the clock runs out of energy and stops.

In this investigation, you will build a pendulum clock that accurately measures a time interval on one minute. You will need to choose an amplitude and number of weights that will keep the pendulum swinging for a least one minute. You will interpret your graphs from investigation 1.54 to figure out how to set up you pendulum.

Setting up the experiment:

1. To begin, choose how many periods of your pendulum will equal one minute.

 Record the number of periods: ______

2. Divide 60 seconds by the number of periods you chose in step one. The result tells you how long each period should be.

 Record the length of each period: ______3. Find your graph of string length vs. period from investigation 1.54 The Pendulum. Use your graph to figure out the string length that will produce a period of the length you chose in step 2.

 Record your string length: ______

4. Set up your pendulum. Be sure to choose an amplitude and number of weights that will keep your pendulum swinging for a least one minute.

Doing the experiment:

1. Test your clock using a “stopwatch of science” Assign one person in your group to start and stop the timer. Choose another person to tell the timer when to start and stop the clock. As the pendulum swing, this person will count the number of periods of the pendulum that should equal one minute.

2. Adjust your string length until you get a pendulum clock that is accurate to within two to three seconds of a minute or better. Do a minimum of 5 trials.

3. Record your data for each trial in the table below. Making a 1 Minute Clock Actual time taken to complete # of periods that should equal String length the chosen # of periods. 1 minute (cm) (seconds)

Thinking about what you have learned:

1. If mass has little effect on the period of a pendulum, why do you think pendulum clocks are built with heavy pendulum bobs?

2. What is the difference between you best “actual time” and 60 seconds?