While I was at University, I took part in a project to create some toys to demonstrate physical principles like the Doppler effect to children. I came up with this neat little toy called the Doppler Ball, which I built and demonstrated (this little sucker made the difference between graduating and having to repeat my final year).
When I was doing my PGCE training I actually used it in anger, and it worked quite well, so I present here a construction and user's guide for anyone who's interested.
Doppler Ball Construction Guide
This guide will enable you to construct your own Doppler Ball. In the interests of
safety it should be noted that construction of the Doppler Ball involves the use of a
soldering iron and sharp knives, and therefore
school students should only construct the Doppler Ball under supervision.
Introduction
The Doppler Ball is a simple toy that can be used to demonstrate the Doppler Effect. It's a simple foam ball with a buzzer inside. When you throw the ball around, the motion distorts the sound produced by the buzzer, thereby demonstrating a Doppler shift.
Materials and Tools needed
- 1x sponge ball, between 15 and 20 centimetres in diameter
- 1x 9 volt buzzer (the ideal frequency for this is 60Hz, so get one at this frequency if you can)
- 1x 9 volt battery
- 1x Batter clip
- 1x Latching switch (the kind that you depress once to close the circuit, and again to open it)
- Connecting wires
- A sharp knife or scalpel
- Masking tape (or equivalent, eg gaffer tape)
- Soldering iron
- Glue (must be suitable for porous materials, e.g. PVA)
Estimated cost: £5.00
Instructions
- The first thing to do is build the buzzer circuit. To do this, user the solder to connect the battery clip, switch and buzzer in series, making sure the connections are strong. The completed ball will need to endure a fair amount of stress. You may wish to mount these parts on a piece of plastic.
- Place the battery in the clip and test the circuit.
- Wrap the components together into a tight bundle and seal with the tape. You will need to make sure the switch is in a prominent position and can be accessed easily.
- Next, prepare the sponge ball. To do this, cut a slit into the ball large enough for the buzzer circuit to be pushed through. The slit should go down to roughly the centre of the ball.
- Excavate some of the foam at the centre to make a cavity for the circuit.
- Place the circuit inside the ball and fill in any space with the foam you previously removed. The circuit shouldn't be allowed to move about too much.
- Mark the position of the switch on the outside of the ball with a marker pen. You can then push on this spot to activate the buzzer.
- Seal the slit using a suitable adhesive. When it's dry, the Dopper Ball is ready for use.
Using The Doppler Ball
You can use the Doppler Ball in a number of ways. One of the most effective is to tie a cord around the ball, and swing it around. As you increase the frequency of the swing, the Doppler shift observed will increase.
Alternatively, you can have two students (who are good throwers) stand a distance apart and throw the ball to each other. If all goes well, the thrower should notice a decrease in the pitch, and the receiver will notice an increase.
Project Contributors: Gavin Brown, Stuart Butler, Andy Franqueira, Pat Hargreaves, Gareth Scaddan, Adam Stow