Doppler Shift!

Curriculum links:

• Physics – Forces, energy and sound – Explore how sound travels through materials

Learning objectives:

1. Explore sound and Doppler Shift
2. Observe the effect happening every day in real life.

Materials:

• Something that makes a constant sound
• A piece of strong string or rope

Safety:

• To prevent anything from getting hit and broken during the experiment, do the experiment in an area with a lot of room – Maybe try it outside!

Instructions:

For this investigation you’ll need something that makes a consistent sound and a piece of strong string. This could be a buzzer or similar but whatever you’re using, you need to be careful to:

1. Not let go
2. Have the rope secured safely
3. Not whack into anything when swinging.

Once you’re happy and you give your apparatus an auld swing, you’ll observe that when the buzzer or sound source is moving towards you, in effect, it is catching up slightly with its own sound waves. With each sound of the buzzer, the source is a little closer to you. The result is that the waves are squeezed together, and more of them reach your ear each second than if the buzzer were standing still.

Therefore, the pitch of the buzzer sounds higher. So, what do you think will happen with the buzzer is moving away from you? Are the waves getting closer together or further apart and what does that do to how the sound appears to you? Have a think or even try it out!

How it works:

Sound is made up of vibrations. These are called sound waves and they are what we hear. These sound waves are formed by objects shaking back and forth. They travel through air, water, and solid objects as vibrations. When they reach our ears, these waves make our eardrums vibrate. This sends signals to the brain and it figures out what we’re listening to. When a something that is making a sound moves in relation to you, its pitch changes. Pitch can be fast or slow, so it depends on speed with typically high pitch being fast and low pitch being slow. From hearing the Doppler Effect you can determine whether the source is moving toward or away from you, and by researching more, you also can estimate how fast it’s going.