1. Sound

2. Sound
Sound travels in solids, liquids and gases. If there is no air, sound will not travel.
An electric bell is placed inside a jar. You hear the bell when you turn on the switch. Could you hear it if the air is pumped out?

3. Sound Sounds are made by vibrating objects Eg guitar strings
Drum skins

4. Sound The sound is carried through the air in sound waves.
These spread through the air.
The energy from the vibrating source is transferred from particle to particle as the sound waves travel.

5. Speed of Sound
Sound travels at 330metres per second in air at 0°C. It travels faster in other substances.
Substance
Speed of sound ms ⁻ᶦ
Air (at 0°C)
330
Air (at 15°C)
342
Oxygen (at 0°C)
317
Water (at 0° C)
1410
Wood (at 20° C)
5000

6. Wavelength

7. Light is one type of electromagnetic radiation. Name 3 others...
The electromagnetic spectrum is the range of all types of EM radiation. Radiation is energy that travels and spreads out as it goes –
Eg the light from a lamp
Radio waves from a radio station
The other types of EM radiation that make up the electromagnetic spectrum are microwaves, infrared lights , ultraviolet lights, x rays, and gamma rays

8. Sound Waves
Radio waves have very long wavelengths of around 10m. The radiation with the shortest wavelength is gamma radiation, a very high-energy radiation which causes injury to the cells of living things.

9. ? Which types of radiation can be detected by the human body?
Which types of radiation can be used for communicating with other people?
Which type of radiation is commonly referred to as heat?

10. marksscience.weebly.com
If finished, watch ‘Can you trust your eyes?’ Youtube. (only if you have your earphones)

11. Sound Facts How is sound caused? How does sound travel and reflect?
Why does sound travel faster through wood than air?
How is sound detected?
How are different pitches (notes, frequencies) in sound caused?
What do you need for sound to be detected?

12. How is sound caused?
Sounds are caused by objects moving backwards and forwards (vibrating).

13. How does sound travel and reflect?
When the molecules at the end of something (eg a tube of air or a metal rod) are disturbed, they vibrate. These molecules collide with molecules further along the material and make them vibrate. This process continues through to the end of the material, which will vibrate any other material that is attached. Sound travels at different speeds in materials of different densities and is reflected off surfaces.

14. Why does sound travel faster through wood than air?
Sound travels better through solids (and liquids) than through air. The reason for this is that sound is a compression wave that is propagated by vibrating atoms knocking into adjacent atoms and causing them to vibrate in turn. This is a much more efficient process when the atoms are closer together, as they are in solids.

15. How is sound detected?
Our ear drums vibrate when air molecules collide with them. This vibration is send to the brain. Electronic devices such as microphones also detect sound. They turn the kinetic energy of the air molecules in to electric potential energy of electrons, causing current to flow.

16. How are different pitches (notes, frequencies) in sound caused?
The length of the material causing the sound will affect the pitch of the sound generated. The tension (tightness) in a wire or string will change the pitch of the sound that it makes when vibrating.

17. What do you need for sound to be detected?
A vibrating source;
A medium through which the sound travels; and
A detector.

18. Why do you hear thunder after you see the lightning?
Light travels about a million times faster than the speed of sound.

19. Light Waves and Refraction
The speed of light in glass is 1.98 x 10⁸ ms⁻ᶦ (slower than air). When light passes from air to glass it does not keep travelling at the same angle, it slows down and bends towards the normal.

20. Colours and Wavelength
Each colour from the spectrum has its own wavelength. Violet light as the shortest wavelength and red has the longest.

21. Wavelengths Why does violet light refract more than red light?
Different wavelengths of light have slightly different speeds in glass.
This means violet light beds more than red
That's why a rainbow forms when sunlight passes through the drops of water in rain

22. Your turn...
Exercises page 146 Science World 9.