# Physics (P3)

Everything in the extension part of physics

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• Created on: 21-05-12 13:58

## Moment

Moment

A moment is the turning effect of a force.

Moment = distance from axis * force
Nm     m N

Increasing the distance from the pivot decreases the force needed and vice versa.

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## Centre of mass

Centre of mass

The centre of mass of an object is the point where its mass is concentrated.

In symmetrical objects the centre of mass is where the two lines of symmetry cross.

The centre of mass always falls directly below the point of suspension.

This means that in non-symmetrical objects, if you suspend it from two different points, where the lines down from the point of suspension cross is the centre of mass.

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## Stability

Stability

Stability is a measure of the tendency of an object to topple over.

Stability is measured by drawing a line perpendicular to the ground from the centre of mass, this is called the line of action, and it shows the effect of gravity on the object.

If the line of action is outside the base of an object the object will topple over.

Stability can be improved by
*Widening the base of an object
*Lowering the centre of mass

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## Centripetal force

Centripetal force

A object moving in a circular path has centripetal force acting on it. The object is accelerating towards the centre of the circle, as the direction is constantly changing.

Force = mass * acceleration

Radius also affects centripetal force, the smaller the radius the greater the force.

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## Gravity

Gravity

Gravity is a attractive force. All objects with mass possess gravity. Gravity depends on the mass and distance from the centre of a object.

Bigger mass = More force (gravity)

Smaller distance = more force (gravity)

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## Universe

Universe

Ideas about the universe have been changing for centuries. Originally it was thought the earth was cente of the universe (this fitted with biblical views). However this view was rejected as the movement of the planets could not be predicted (not for lack of trying, according to the time planets had very complicated orbits involving lots and lots of circles (look up Ptolemy)). Eventually Copernicus suggested the sun was centre of the universe (heliocentric) (Shock, horror, HERECTIC). However his universe still couldn't be predicted. Kepler then suggested that the planets had eliptical orbits (squished circles). Now the universe acctually works and the movement and placement of the planets can be predicted accurately).

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## Satellites

Satellites

A satellite is a body that orbits another body (e.g. earth around the sun, the moon around the earth etc).

There are two types of artifical satellite (the above examples are natural). These are geostationary and polar.
Geostationary
*These stay in the same position above the earths surface. This makes it useful for TV stuff, spy (ahhh), weather.

Polar
*These orbit from pole to pole.
*they are useful for, GPS (ahhh), weather, environmental observation.

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## Big Bang Theory

Big Bang Theory (not the TV series)

Okay, the formation of the universe on 1 card.

1. Lots and lots of energy in one place (about the size of a atom)
2. The above energy expands (expodes) rapidly.
3. Energy becomes matter (taadaa), such as hydrogen and helium atoms
4. Clouds of gases (hydrogen and helium) begin to swirl.
5. Atoms begin to fuse together in the gas cloud and produce energy, and larger molecules.
6. Lots and lots of energy is released as heat and light, A STAR is created.

pretty cool right

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## Life cycle of a star

Life cycle of a star
1. A star is formed as in the previous card (but if you want to be really scientific the gas cloud is a stellar nebula)
2. The star lives for a time, running mostly on hydrogen. The star stays together because of the nucleur fusion energy pushing outwards, which is equal to the gravity going inwards.
3. The star nearly runs out of hydrogen, so uses helium. However it is now a red giant, and bigger than before.
4. The outer layers of the star expand and the centre becomes denser. It is now a planetary nebulla.
5. The star cools down a lot, and becomes really dense. It is now a white dwarf.
It's basicaly the same for huge stars except in point 4 there is a supernova (really big explosion) and then it becomes either a black hole (sucks in everything) or a neutron star (really dense).

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## Reflections

Reflections

The colour a object looks is the colour(s) it reflects.

There are 3 types of mirror.
Plane
*Produce virtual images, that are the same size, and the right way up.

Convex (the stick out ones)
*Produce virtual,  diminished, right way up images.

Concave (the stick in ones)
*Depend on the position of the object in relation to the focus points. So basically it can be anything (use a ray diagram)

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## Ray diagrams for mirrors

Ray diagrams for mirrors

1. In parallel, out through focus, but it should really reflect off the mirror

2. In through 2nd focus, reflect back on its self.

Always draw the direction of the rays on the diagram. Where the lines cross is the image.

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## Refraction

Refraction

Refraction is the bending of light rays as they travel through substances of different densities.

When light slows (denser material) it refracts towards the normal line

When ight speeds up (less dense material) it refracts away from the normal line.

Refraction is the reason white light can be split into seperate colours. The colours all have different wave lengths as so bend at a different rate. This produces a rainbow effect.

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## Lenses

Lenses

Lenses change the way we see something. They focus the light on a different point. Our eyes contain lenses.

Converging lenses are convex (so they stick out), and they focus the light inwards.

Diverging lenses are concave (so they go in), and they spread the light apart.

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## Drawing ray diagrams for lenses

Drawing ray diagrams for lenses

1. In parallel, out through focus.
2. In through focus, out parallel.
3. If it goes straight through the centre of the lense, it will not bend or refract.

Again always draw on the direction of the ight, and where the lines cross is the image.

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## Sound

Sound

Sounds are caused by vibrations, but need particles to travel through (which is why in space no one can hear you scream (sorry)).

Pitch = frequency, so the higher the frequency the higher pitched the note is.

Amplitude (height of wave) = volume, so the taller the wave the louder the sound.

Waveform is the shape of the wave and varies due to sound type.

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## Ultrasound

Ultrasound

Ultrasound is higher than people can hear so 20,000Hz +. People can hear between 20-20,000Hz.

Ultrasound has various uses including
*Pregnancy picture thingy
*Pest scarer (really annoying noise, some teenagers can hear it)
*Cleaning delicate stuff like watches

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## Motor effect

Motor Effect

Magnetic fields go from north to south.

Electricity flowing through a wire creates a magnetic field. The direction of the field can be worked out throught the right hand rule.

When two magnetic fields are perpendicular to each other movement occure. This is called the motor effect (using electricity to create movement).

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## Electromagnetic induction

Electromagnetic induction

Electromagnetic induction is using movement to create electricity, and is used in generators and bike dynamos.

1. A magnet is moved.
2. Alternating potential differnence is created.
3. Current begins to flow, if in a closed circiut.
4. Electricity is formed

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## Transformers

Transformers (not the weird robot things)

Transformers can be used to step up or step down the voltage of electricity.

V1/V2 = N1/N2

The electricity in the first coil (a.c.) produces a alternating magnetic field. This produces a alternating potential difference, and if the circuit is closed current flows.

The coils are wrapped around a iron core, which doesn't conduct, but increases the magnetic field strength.

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Report

this is P2...

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No its not

Its P3 for GCSE on the AQA board, you might be on a different board, or they changed it recently, it might be different for next year?

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Thankyouu this was sooooooooooooooo helpful.... i think i might actually pass this subject now btw it is p3 thanks again :D

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this is so useful!

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this is a useless resource with no info whatsover for what i require

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this is actually p2

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