Science corner

18th February 2005 at 00:00
Sophie Duncan shows how a slinky helps in exploring waves

Slinkys are wonderful toys, and the basis for lots of fun experiments. These two demonstrations allow your students to explore waves.

Sound waves are a type of longitudinal wave. You can make a longitudinal wave using a slinky. Two students should each hold an end, and stretch the slinky out a little. Wait until it is still.

One student should then make a sharp horizontal movement with the end of the slinky. This may take a little practice. The aim is to send a wave along the slinky to the other student. The wave will rebound when it reaches the other end. If you watch carefully, you will be able to see the coils get pushed together as the wave travels.

When you shout into a cave, molecules of air are vibrated just like the coils of the slinky. As each molecule of air bumps into the next, energy is transferred. Just like the reflection at the end of the slinky, sound will bounce off the inside of the cave, giving an echo. (The amount the sound reflects depends on what the surface is like.) You can also demonstrate transverse waves using a slinky. Light is an example of a transverse wave. Stretch out the slinky between two students.

At one end, it should be held stationary, and at the other end, the student should move it up and down, and then stop. Encourage the class to watch how the wave moves.

You can also explore what happens when the reflected wave interferes with the outgoing wave by moving one end of the slinky up and down continually.

It is really important to keep the other end still - so if students find this hard, tie one end to a stationary object. At certain frequencies (this relates to how quickly you move the slinky up and down), you get patterns where there are parts of the slinky that do not move at all. These are called nodes. You should be able to make several patterns.

These waves are called standing waves.

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