# Physics (P4, P5 + P6) - Revision Notes

A friend's Physics Revision notes, for P4, P5 and P6.

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• Created by: Alex
• Created on: 20-05-11 16:50

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Physics Modules P4, P5 and P6
Module P4 ­ Explaining Motion
Speed:
Speed is the distance travelled in a certain time.
To find the speed of an object you need to know the distance
travelled and the time it takes.
Using the speed triangle cover up the letter you want to find.
Speed is rarely constant, you accelerate and decelerate.
So speed is normally average speed, even instantaneous speed is
average speed, but over a really short period of time.
Speed and Velocity:
speed, flat sections = no speed, steeper graph =
faster, `downhill' means coming back to starting
point, curves show acceleration or deceleration,
steepening curve means speeding up, a levelling
out curve means slowing down.
Speed is the gradient of a graph, so you
divide the vertical by the horizontal (so travel
300m in 20s, 300/20 = 15 m/s)
Distances can be positive or negative; it
just means that they are travelling in opposite
directions.
Speed is just a number, velocity has a
direction too.
It is more useful than speed.
Scalar quantities ­ Mass, speed, time length ect
Vector quantities ­ Force, velocity, acceleration, momentum ect
Velocity:
Velocity can be positive or negative which shows direction.
Velocity time graphs ­
o Straight increasing = Acceleration or deceleration
o A curve shows increasing or decreasing acceleration.
Tachographs plot speed against time so you can see how far someone travels. This is used in
lorries so they don't drive too far without a break. They are those circle things.
Forces and friction:
Forces occur when two forces interact (interaction forces).
If you push against something it pushes equally hard back.
So you push down on a table with 10N of force, it pushed back with 10N or it breaks, and
dies, and sets on fire.
Moving objects experience friction;
o Friction between two gripping forces which stops them from moving.

## Other pages in this set

### Page 2

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Friction between two sliding surfaces.
o Resistance from liquid or gas. You push the molecules out the way causing friction,
which is why you get friction, think aerodynamics.
Forces and Motion:
Arrows show the size and direction of force, a larger force = longer arrow.
If you have one force bigger than another the object moves, if they are equal then it doesn't
move.
A resultant force shows the speed and direction the object will go.

### Page 3

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Kinetic energy is movement.
Anything moving has kinetic energy, the greater the mass and speed the bigger the kinetic
energy (J).
Kinetic energy = ½ x mass x velocity²
To increase something KE you need to increase its speed. The only way to do this is to apply a

### Page 4

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Circuits ­ The basics:
The standard circuit has an ammeter, a voltmeter in parallel with a component, and a
variable resistor. Oh, and a battery. Obv.
Voltmeters measure the potential difference between two points. So you have one
around the battery and one around the component so you can see how much energy
the component takes out compared to the amount of energy produced by the
battery.
Resistance:
The slope of a voltage current graph shows the

### Page 5

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If one thing disconnects, the circuit is broken, so they aren't very handy and very few things
are connected.
Potential difference (Voltage) is shared around the components. V = V + V
Resistance adds up, so if 4 components are in the circuit 1 with 5 ohs, 1 with 3 ohms ect, the
Cell voltages add up too, so three 12v batteries will mean the circuit has 36v in it.…read more

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Primary coil produces a magnetic field, which stays in the iron core.
Because it is AC the magnetic field is constantly changing.
The changing magnetic field induces an AC current in the secondary coil.
The relative number of coils in the secondary coil determines more or less voltage.
If you supplied DC to the primary coil, you'd get a magnetic current but no induction because
you need a changing field to induce voltage.
TRANSFORMERS ONLY WORK WITH AC, NOT DC.…read more

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Ripples on water.
o Waves on strings.
o A slinky wiggled up and down.
In transverse waves the vibrations are at 90° to the
direction of the wave.
Longitudinal waves have vibrations along the same line.
o Sound and ultrasound.
o Shock waves (seismic waves)

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Wave Interference:
When waves meet they cause disturbance.
When waves are in step you add the placement, when they aren't you subtract it.
Interference of light makes bright and dark patches.
Constructive interference makes it bright, destructive interference makes it dark.
Light and sound must be waves because
o They can diffracted (bend around an object)
o Reflected
o Absorbed
o Transmitted
o If light acted like particles there wouldn't be any positive or negative disturbance,

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Bones absorb it, flesh doesn't, so where it goes through you turns the plate black,
and where your bones are it stays white.
o There also used in airports.
Infrared and light are used in optical fibres.
o The single doesn't weaken much.
Information is converted into signals.
o 2 waves you can send information as
waves, AM and FM.
AM radio waves have varying amplitude.
o An AM radio transmitter sends out a