Sound and Heat

Sound

-When an object vibrates it produces sound.

-The faster the vibrations the higher the sound.

-This is also known as the frequency (f) which is measured in Hertz (hz).

-An oscillosope shows the wave pattern of sounds.

-A low frequency note means a low or bass note is produced.

Sound

-Loud sounds have more energy which means that the ampiltude is higher and the wavelength is shorter.

-The amplitude is how much energy a sound has and is shown on the oscillosope as the height of the wave.

-The wavelength is the distance between each wave.

- Because sound is produced by an object vibrating backwards and forwards the maximum distance the particle moves from the starting position is known as the amplitiude.

Speed of Sound

-Sound travels fastest in a solid because the particles are close together which means the particles can easily collide and pass on sound energy to each other and the material is more dense.

-Thunderstorms are proof that light travels faster than sound because you see lightning before you hear it.

-The further away you are from a thunderstorm the more the sound has to dissipate or spread out for you to hear it, this makes the sound quietet and is very difficult to hear.

-The speed of sound in air is 330 metres per second.

-The speed of sound in water is 1500 metres per second.

Echoes

-Echoes are when sound is refelcted of a surface.

-Harder surfaces reflect sound more than softer materials.

-Fishermen use echo-sounding or sonar to locate shoals of fish.

-Sound waves are sent to the sea bed and is a shoal of fish is passing under the boat the sound waves are reflected by the fish and the echo gets back to the boat more quickly because their is a shorter distance for the sound to travel.

-In echo-sounding the sound waves need to travel to the sea bed and back so the time it takes to get to the bottom of the sea is half the total time for the whole journey.

-The Speed of Sound is calculated by using this equation:
Speed of Sound equals distance travelled over time taken

-So if the speed of sound in air is 330 m/s the distance the sound would have travelled in 3 seconds is 330 multiplied by 3 which is 990 m/s because the equation is:

-Speed of Sound (330) = Distance (what we are trying to find out) multiplied by time (3).

-Rearange it and you get 330 multipled by 3 which is 990 m/s.

Worked Example:

Calculate the speed of sound in a metal raliway track that is 1200 metres long if the sound is heard 0.55 seconds after it is heard at the other end.

Step 1

Speed of sound = 1200 over 0.55

Step 2

1200 divided by 0.55 = 2181.82

ANSWER= 2181.82 m/s

Making Waves

-Pushing one end of a spring back and forward makes a 'push wave'.

-A pulse or wave of energy passes through this type of wave.

Compression and Rarefraction.

-Compression is a high pressure area where particles are close together.

-Rarefraction is a low pressure area where the particles are further apart.

-During a wave the enedy passes through a spring in the same direction forwards and backwards, this wave is called a longitudinal wave.

-The energy is TRANSMITED through the wave.

Compression and Rarefraction

-The particles in the spring vibrate backwards and forwards from their original positions, they do not move along the spring, so the particles in the coils transmit the energy through them.

-When a person speaks or shouts their vocal chords vibrate and this sets up sound waves that are transmitted by the particles through the air.

-When a loud speaker produces a sound the cone inside the speaker vibrates forwards and backwards very quickly.

-When the loudspeaker cone moves forward the air particles are pushed close together, the pressure rises and makes a high compression.

Sound Travels

-The sound energy is passed on the air particles move and bump into each other, the compression moves outwards through the air.

- When the cone is moved backwards the air molecules are pulled apart, the air pressure falls and rarefraction is produced.

-Every time the cycle repeats a new sound wave is produced.

-This action creates a series of waves that transfers the energy from the loudspeaker outwards as a wave.

-As a person moves away from the sound source the sound energy becomes dissipated (spread out) and is harder to hear.

Sound and Particles

-In air the particles are free to move since the particles are not joined together.

-A sound wave passes through the air because the moving particles bump into their neighbours.

-When they collide the particles pass the vibration energy on to each other and the sound wave passes through the air because of this.

-All materials are made from particles.

- In gas the particles are far apart so they collide less frequently and cannot pass on the energy as fast as in liquid.

Sound and Particles

-In a liquid the particles are closer apart than in gasses but further apart than in solids.

-This means they collide more often and pass on energy a bit faster than in liquids.

-The liquid particles are packed more dense.

-In a solid the particles are packed closely and vibrate in a fixed position which means the particles are always colliding which means they pass energy alot more often.

-So putting our ear to the ground does enable us to hear quicker.

Human Hearing Range

-As the frequency of a sound increases the pitch becomes higher until it is no longer heard.

-The human hearing range is 20 Hz to 20 000 Hz.

-Sounds above this are known as ultrasonic sounds.

-As we get older the upper threshold which is the higher end of the range lowers.

-Because ultrasound is so easy to control it has many uses.

Ultrasound

-Ultrasound is used in medicine to scan vital organs.

-Kidney stones are broken up without need for surgery, the high frequency vibrations cause the kidney to vibrate and break up.

-In dentistry ultrasound is used to remove plaque from teeth as the freqency makes the plaque vibrate and fall of, this method is used to clean many different objects.

-Bats and dolphins use echolocation to communicate and navigate, they send out clicks and depending on the type of echo they get back they know if they need to attack or hide.

Structure of the Ear

-The ear is divide into three sections: the inner ear, middle ear and outer ear.

-The outer ear is seen on the outside of the head.

-The parts that enable us to hear the sound are very delicate and are protected by the skull, the middle and inner ear.

- The sound travels through the ear like this:

-An object creates sound waves, the waves then go to the eardrum and cause it to vibrate which makes the ossicles vibrate causing the cochlea to vibrate which means the hair cells lining the cochlea vibrate and cause the auditory nerve to turn it into nerve impulses which the auditory nerve takes to the brain.

How are ears damaged?

-The ear canal can become blocked with wax.

-Very loud sounds can tear or rupture the ear drum.

-Infections can occur.

-The ossicles can stick together.

-The cochea can become damaged.

in general:

Sound vibrations not being transmitted correctly.

nerve cells can become damaged.

The loudness of a sound is measured in Decibels (dB)

-As sounds get louder their decibel level rises.

-The quietest sound is 0 dB.

-Some people work in noisy places which means they must wear ear protection.

-Some companies reduce the time workers are exposed to the loud sound.

-The government has recently passed new laws to limit noise levels in workplace.

-When an object is hot or cold we are comparing it with another object.

-Heat is a type of energy .

-Temperature is a way of measuring how hot or cold something is against an agreed scale.

-The units are degrees celcius and can be found out using a thermometer.

-Heat is a measurement of how much energy an object has.

-If there is a difference in temperature between an object and its suroundings there is a heat flow.

-Heat always flows to cold areas.

-If an object is placed in cooler surroindings heat flows into the surroundings.

-If you touch a light bulb when it is on you can burn yourself.

-Most of the electrical energy is transferred into heat energy, only a small amount of energy produces light energy.

-Some lamps are specially designed to give out heat such as infra-red lamps.

-A microwave is an easy way to heat up food containing water.

-The microwave energy is set just right to be absorbed by the water in the food, as the particles gain energy they bump into each other and pass on heat energy.

-In this way the whole food product is cooked.

-Heat can move from one place to another.

-Metal is a good heat conductor while plastic or wood is an insulator.

-Heat energy goes to where it is cooler, we say it has been conducted to the cooler surroundings.

-Conduction mostly happens in solids .

-Liquids and gasses are poor conductors of heat.

-Solids are good conductors of heat because the particles in a solid cannot move.

-When one end of a solid rod is heated the particles start to vibrate and gain heat.

-The particles bump on the energy and the heat energy is passed down to the other end.

-Rising hot air creates thermals.

-When hot air rises cooler air takes its place.

-This causes a circulation.

-Convection only happens in liquids and gasses because the particles can move freely.

-Convection is the main way heat travels through liquids and gasses.

-It happens when one part of a liquid or gass is heated more than the rest.

-The warmer liquid or gas expands when it is warmed up because the particles gain energy and are moving about, they need more space.

-This expansion means that it is less dense than its surroundings.

-Convection causes wind and ocean currents as the moving gas and liquids carry heat from where it is hotter to where it is cooler.

-The same principle is used at home in central heating.

-A radiator or heater warms up the air next to it which then rises, cold air takes its place and gets heated and the proccess repeats, untill the whole room is heated.

-Heats travels from hot areas to cool areas because the particles are free to move.

-Liquids and gasses are called fluids because they can move.

-When a fluid is heated the molecules move faster and the fluid expands, this reduces the density of the warmer part of the fluid, the less dense parts moves upwards through cooler parts, as they move they loose heat to the surroundings and cool down again which means they fall.

-The type of energy that comes from the sun is called solar radiation.

-Cloudy days are cooler than clear days because this type of radiant heat travels in straight lines, it cannot go round the clouds.

-Clouds refllect alot of heat back into the atmosphere.

-When radiant heat reaches earth it is absorbed by surfaces.

-White materials reflect light while black materials absorb.

-All hot objects give of (emit) radiant heat, the hotter an object is the mroe heat it radiates.

-Light shiny surfaces are not as good as emmiting radiant heat.

-In space there are no particles present so radiant heat must rely on a differnet method of energy transfer.

-Electromagnetic waves carry the radiant heat.

-The waves transfer energy from one place to another without the material its travelling through moving.

-Heat radiation is carried by ultra-violet and infra-red rays.

-When bread is toasted under a grill the heat must travel downwards from the grill elements on to the bread.

-The bread absorbs this heat energy and warms up the bread.

-The radiation still transfers the heat energy even thought there are no air particles around it.