sound waves

sound waves and matter

Most of the sounds we hear reach our ears through the air, but sounds can also travel through liquids and solids. If you swim underwateror even submerge your ears in bathwaterany sounds you hear have traveled to your ears through the water. Some solids, including glass and metals, are very good at transmitting sounds. Foam rubber and heavy fabrics, on the other hand, tend to muffle sounds. They absorb rather than pass on the sound energy. Q: How can you tell that sounds travel through solids? A: One way is that you can hear loud outdoor sounds such as sirens through closed windows and doors. You can also hear sounds through the inside walls of a house. For example, if you put your ear against a wall, you may be able to eavesdrop on a conversation in the next roomnot that you would, of course.

defining sound

In science, sound is defined as the transfer of energy from a vibrating object in waves that travel through matter. Most people commonly use the term sound to mean what they hear when sound waves enter their ears. The tree above generated sound waves when it fell to the ground, so it made sound according to the scientific definition. But the sound wasnt detected by a persons ears if there was nobody in the forest. So the answer to the riddle is both yes and no!

how sound waves begin

All sound waves begin with vibrating matter. Look at the first guitar string on the left in the Figure 1.1. Plucking the string makes it vibrate. The diagram below the figure shows the wave generated by the vibrating string. The moving string repeatedly pushes against the air particles next to it, which causes the air particles to vibrate. The vibrations spread through the air in all directions away from the guitar string as longitudinal waves. In longitudinal waves, particles of the medium vibrate back and forth parallel to the direction that the waves travel. Q: If there were no air particles to carry the vibrations away from the guitar string, how would sound reach the ear? A: It wouldnt unless the vibrations were carried by another medium. Sound waves are mechanical waves, so they can travel only though matter and not through empty space.


a ticking clock

The fact that sound cannot travel through empty space was first demonstrated in the 1600s by a scientist named Robert Boyle. Boyle placed a ticking clock in a sealed glass jar. The clock could be heard ticking through the air and glass of the jar. Then Boyle pumped the air out of the jar. The clock was still ticking, but the ticking sound could no longer be heard. Thats because the sound couldnt travel away from the clock without air particles to pass the sound energy along. Click image to the left or use the URL below. URL:

instructional diagrams

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all sound waves begin with vibrating matter.

-->  a. true

b. false

vibrations spread through the air in all directions from a vibrating object.

-->  a. true

b. false

sound waves are

a) surface waves.

b) transverse waves.

-->  c) longitudinal waves.

d) none of the above

sound waves can travel only through gases.

a. true

-->  b. false

materials that tend to absorb rather than transmit sound waves include

-->  a) foam rubber.

b) glass.

c) metal.

d) all of the above

sound waves are mechanical waves.

-->  a. true

b. false

diagram questions

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