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2 Frequency

Frequency is how many times an event occurs in a specific amount of time, such as the back and forth swing of a pendulum. A pendulum is an apparatus with a hanging weight from a fixed point that can move freely back and forth. A string with a washer attached to the end is one example of a pendulum. The weight on a pendulum is called the bob. Each forward and back swing of the bob on a pendulum is counted as one cycle.

The frequency of a pendulum is determined by counting the number of cycles, the back and forth movements, the pendulum bob makes in a one-second interval. The length of the cable or string attached to the bob determines the pendulum's frequency. The longer the string, the lower the pendulum's frequency.

See for Yourself

Materials

 string, 18 inches (45 cm)

 washer with a hole, or any comparable weight

 tape

What to Do

1 Tie one end of the string to the washer.

2 Tape the free end of the string to the edge of a table. Leave part of the end of the string free. This end of the string will be pulled to shorten the string.

3 Pull the washer to one side and release it. The washer should freely swing without touching anything (Figure 1).FIG 1

4 As the washer swings, slowly pull the end of the string to shorten it. As you shorten the string, observe the change in the frequency of the pendulum.

What Happened?

As the length of the string is shortened, the distance the bob swings gets shorter. Thus, it takes less time for the bob to swing back and forth. This means that, given the same interval of time, a shorter pendulum will swing back and forth more times than a longer pendulum. So, there is a relationship. The frequency of a shorter pendulum is higher than the frequency of a longer pendulum.