Sound Requires a Medium for Propagation

Place an Electric bell in an air filled jar. You can hear the sound of the electric bell which is ringing.

Now, suck out the air from the jar using a vacuum bump. As you sucking the air out, the sound starts fainting. As all the air sucked out, the sound fully faints. This experiment confirms that a medium is required for the propagation of sound.

Sound Travels through Solids
Ask your friend to hit the bench using a stick at one corner. Keep your ear on the bench at the other corner. As your friend hit the bench, you can hear the sound at the other corner. This confirms that sound travels through solids.

As soon as the train departs from the plat form, you keep your ear on the train track and you can hear the vibrations of the motion of train.

Sound Travels through Air (Gases)
What you hear is the propagation of sound through air. If there is no air, we canâ€™t hear the sound inside the room.

We all hear the sound of the moving flight. It is due to the propagation of sound through air (gases) which reaches our ear.

Sound Travels through Water (Liquids)
Place the bell in a beaker filled with water and make it sound .You can hear the sound, which confirms that sound can travel through liquids.

Communication between dolphins also confirms that sound travels through liquids.

Activities
Does sound travel through paper? through plastic? through metal?

• Put a ringing alarm clock in a paper bag.
• Close the bag. Can you hear the clock ringing now?
• Repeat steps 1 and 2 using a plastic container and a metal can.

Does sound travel through water?

• Fill a glass jar nearly full of water.
• Have your friend cover one ear with her/his hand. Put the other ear against the glass jar.
• Ask another friend to hit two spoons together under water.

Do you hear a sound?

Sound travels through different kinds of matter. Sound travels through gases, liquids and solids.

Group: What kind of matter does sound travel best in--air, water, wood or metal?

A. 1. Hold a plastic bag of water against one of your ears. Cover your other ear with your hand. Have someone hold a ticking clock against the bag of water. Listen.

2. Keep the clock in the same place. Remove the bag of water. Listen.

3. Place a block of wood between your ear and the clock. Listen.

Do you hear the clock best through the air, the water or the wood?

B. 1. Place the clock 20 cm away from your ear and listen to the ticking.

2. Have your partner hold the clock at the 20-cm mark on the meter stick. Place your ear at the end of the meter stick and listen.

3. Have your partner hold a metal rod to your ear and place the clock against the rod 20 cm away from your ear. Listen. Does sound move differently through some solids than it does through others? Find out.