Properties of Waves

Two additional properties of waves include FREQUENCY and PERIOD:

• FREQUENCY: The NUMBER OF WAVES that pass a certain point in ONE SECOND. It's measured in HERTZ (Hz).

• PERIOD (Time Period): The time it takes for ONE COMPLETE WAVE to pass a point. It’s measured in SECONDS (s).

FREQUENCY and PERIOD are connected by the following equation:

Where:

• f is frequency, measured in Hertz (Hz).
• T is period, measured in Seconds (s).

The Wave Equation

This equation is used to work out WAVE SPEED, which is defined as the SPEED at which ENERGY is TRANSFERRED (or the wave moves) through a MEDIUM:

Where:

• v is wave speed, measured in m/s.
• f is frequency, measured in Hz.
• λ is wavelength, measured in m.

Measuring the Speed of Sound

You can work out the SPEED OF SOUND using TWO methods:

Method 1: Direct Measurement

1. Two people need to stand 100 metres apart.
2. Use a TRUNDLE WHEEL or TAPE MEASURE to measure the distance.
3. One person claps TWO BRICKS.
4. The other person uses a STOPWATCH. They start timing when they SEE the blocks clapped and stop when they HEAR the sound.
5. REPEAT this several times and get an AVERAGE time.
6. Use the FORMULA to find the speed of sound:

Method 2: Echoes

1. Two people stand about 50 metres from a large wall.
2. Use a TRUNDLE WHEEL or TAPE MEASURE to measure the distance.
3. One person claps TWO BRICKS.
4. The other person uses a STOPWATCH. They start timing when they SEE the blocks clapped and stop when they HEAR the sound.
5. Repeat several times to get an AVERAGE time.
6. Use the FORMULA to find the speed of sound, but ensure you DOUBLE the distance (50m x 2 = 100m) to account for the distance of the echo returning back.