Sound bounces back

The idea

Sound reflects off solid or liquid obstacles by the same laws as light: incident and reflected directions make equal angles with the normal at the point of incidence, all three lying in one plane.

A clap against a wall

You clap near a big wall. The sound hits the wall and some of it bounces off.

If the sound hits the wall at a slant, how do you think it leaves?

• At the same slant on the other side of the normal
• Straight back along the way it came
• Along the wall

Change the angle

Move the slider to change the angle at which the sound hits the surface. The angle is measured from the normal, the dashed line at the point of incidence.

The same laws as light

Sound can bounce off solids and liquids. It follows the same laws of reflection as light, which you learnt earlier. The directions of the incident and reflected sound make equal angles with the normal, and all three lie in one plane. An echo is a common example.

Sound waves can bounce off obstacles like solids or liquids: reflection of sound. Sound follows the same laws of reflection as light: the directions of the incident and reflected sound make equal angles with the normal at the point of incidence, with all three in the same plane.

Notes

Sound reflects off solids and liquids by the same laws as light: equal angles with the normal, all three in one plane.

Check yourself

Which of these can reflect sound?

Which laws does the reflection of sound follow?

Sound hits a surface so that the incident direction makes an angle of 40° with the normal (an example). What angle does the reflected direction make with the normal, in degrees?

Answer: 40 °

The incident and reflected directions make equal angles with the normal, so 40°.

What is one of the most common examples of the reflection of sound?

• A vacuum. Sound waves can bounce off obstacles like solids or liquids. A vacuum has no matter.
• Nothing, because sound cannot be reflected. Sound waves can bounce off obstacles like solids or liquids, which is the reflection of sound.
• A solid or a liquid — correct. Yes!
• The same laws of reflection as light — correct. Yes!
• Laws that apply to sound alone. Sound follows the same laws of reflection as light.
• No laws, because sound is not a wave. Sound is a wave, and it follows the same laws of reflection as light.
• A sonic boom. A sonic boom is made by an aircraft flying faster than the speed of sound.
• An echo — correct. Yes!
• A tone. A tone is a sound of a single frequency. An echo is the common example of reflection.