The tuning fork

The idea

A tuning fork is a U-shaped metal bar with a stem whose prongs vibrate when struck on a pad, producing a nearly single-frequency sound.

A fork that sings

A tuning fork is a metal tool with two long arms. A teacher strikes it on a pad and holds it near your ear. You hear a clear sound. Then the teacher lets a prong just touch the water in a bowl.

What do you think happens to the water?

• Small waves spread out on the water surface
• Nothing happens to the water
• The water rises up the prong like a thread

Strike and touch

A teacher does this in class. Strike the fork, then touch a prong to the water.

A fork with a nearly single frequency

A tuning fork is a U-shaped metal bar with a stem, usually made of steel or aluminium. The sides of the U are called prongs or tines. Striking them on a pad makes them vibrate. Frequency is how often the vibration repeats each second. Everyday sounds mix many frequencies, but a tuning fork gives a nearly single frequency.

A tuning fork is a U-shaped metal bar with a stem. Its prongs vibrate when struck on a pad, producing a nearly single-frequency sound.

Notes

A tuning fork is a U-shaped metal bar with a stem. Struck on a pad, its prongs vibrate and give a nearly single-frequency sound.

Check yourself

What are the sides of the U of a tuning fork called?

A vibrating prong touches water and waves form on the surface. What does this show?

What is a tuning fork usually made of?

What kind of sound does a struck tuning fork make?

• Prongs or tines — correct. Yes!
• Stems. The stem is the part the U is attached to. The sides of the U are the prongs or tines.
• Pads. A pad is what the prongs are struck on, not a part of the fork.
• The water is making the sound. The waves are caused by the vibrating prong. They show that the prongs vibrate.
• The prongs are vibrating — correct. Yes!
• The prongs are still. If the prongs were still, they would not make waves on the water.
• Rubber or cloth. A tuning fork is a metal bar. It is usually made of steel or aluminium.
• Glass or clay. A tuning fork is a metal bar, usually steel or aluminium.
• Steel or aluminium — correct. Yes!
• A nearly single-frequency sound — correct. Yes!
• A mixture of many different frequencies. Everyday sounds contain a mixture of many frequencies. A tuning fork makes a nearly single-frequency sound.
• No sound until it is placed in water. The sound is produced as soon as the prongs are struck and vibrate. You can hear it near your ear.