1. LO: To investigate how sound travels 08/02/18

2. How does sound travel through solids, liquids and gases?
Unlike light, sound needs a medium to travel through. It cannot travel through a vacuum. Sound is carried by vibrations so it needs a material to vibrate, either a solid, a liquid or a gas.
Moving through a medium
Through solid …
You can hear the sound of a train on a track long before the train arrives. The sound travels down the track faster than through the air. Unfortunately, sound energy is also transferred through solid doors and walls.

3. How does sound travel through solids, liquids and gases?
Whales communicate over many miles using high-pitched sounds which travel through water. We can hear sounds in water through a hydrophone.
… and gas
Most of the sounds we hear travel through the air. But the further away you are from the source, the quieter it seems.

4. Demonstrating that sound needs a medium
With air in the jar, we hear the bell ring. Its vibrations are transferred throught the air and the glass to our ears.
Hammer hits bell → air in jar vibrates → glass vibrates → air outside jar vibrates → sound detected by our ears.
When the vacuum pump has removed the air from inside the jar. We cannot hear the bell as there is nothing to transmit the vibrations away from the bell.

5. Sound transfer and particles
The particle model can help us picture what happens when sound energy passes through a material. The vibrating bell causes compressions in the air near to it. These compressions are transmitted through the air as particles move together and apart.
In a solid the particles are close together, so the vibrations are passed quickly from one particle to the next. Sound travels fastest through a solid.
But sound does not have the same speed in all solids. In a dense solid such as steel, the particles are close together and pass vibrations on faster from one particle to another.

6. Travelling sound
Sounds get quieter as the distance between the sound source and your ear increases.
Sounds travel as vibrations. As the sound waves travel, the particles of whatever they are travelling through vibrate, or move quickly on the spot. The further the vibrations travel, the more they spread out. As they spread out through more and more particles, the vibrations become smaller and smaller. This causes the sound to get quieter and quieter.
Think of dropping a leaf into a pond. The very first ripples directly around the leaf will be very large, but as the ripples spread out across the pond, they will get smaller and smaller until eventually they disappear.
This is why sounds get quieter and quieter as you move further away from the source, until you eventually can't hear the sound at all.

7. Travelling sound
You can see the ripples getting smaller as they spread out across the pond, until they eventually disappear. This is like the way the vibrations of sound get smaller as they spread out over distance, getting quieter and quieter.

8. Sound over distance
We know that vibrations spread out and get smaller as they travel, making sounds quieter as we move further away from the source of the sound. But often people need to be able to hear sounds from far away. Can you think of any devices that transmit sound over a distance, or ways of making sounds louder so that they travel further? Talk to your partner about your ideas!

9. Telephone transmission
Telephones are used to transmit the sound of people's voices over long distances.
When you speak into a telephone, the sound energy in your voice is turned into electrical energy, which is transported down a wire to the other person's telephone.
The electrical energy is converted back into sound energy, and they can hear what
you are saying!

10. Your task today:
In pairs, you are going to be creating your own cup phones to test how sound can travel over distance.

11. What you need to do:
 Punch a small hole in centre of the bottom of each cup
Thread one end of string through the bottom of each cup.
Place a paperclip or toothpick in the bottom of each cup and tie the loose end of the string around it (the clip or pick is just here to keep the string from slipping through the bottom of the cup).

12. Steps to follow!
Give one cup to your conversation partner and hold one yourself.
Walk slowly apart until the string connecting the cups is straight and tight.
Put your cup over your ear and have your partner talk into his or her cup (keep the conversation relatively quiet if you are standing close to one another. •   Can you hear your partner talking? 
Now you try talking into your cup and have your partner listen into his or her cup. Can he or she hear you? •   Try letting the string go slack. Is the cup-and-string telephone still effective? •   Now, keeping your voice at the same level and remaining the same distance apart, try talking to each other without using the cups. Can you hear as well?