Physics.

Explaining Motion.

Interaction pairs forces are equal in size but opposite in direction, they act on different objects.
Vehicles (and people) move by pushing back on something, causing a forward force on them.
Reaction force: the force created to counteract a force, e.g. the weight of a book on a table.
The friction force matches the applied force that is making objects slide
Average speed of a moving object: distance/time taken
Instantaneous speed - speed at a particular instant
Velocity - speed in a certain direction
When a force acts on an object it causes a change in it's momentum
Momentum = mass x velocity
Change of momentum = force x time
Vehicle safety - the longer the impact time the smaller the av. force
Work is the energy which makes an object move
Amount of work = force x distance
When something works, it's energy decreases by that amount and vice versa
Doing work on an object increase it's gravitational potential energy (by liftinf it up) or it's kinetic energy (by making it move faster)
As GPE decreases, kinetic energy increases and alternatives
Change in GPE is '1/2 x mass velocity^2'

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Electric charge cannot be created or destroyed but can be moved from one object to another.
An electric current is a flow of charges which are already present in the materials of the circuit.
The battery makes the charges move around the circuit.
Current doesn't get used up but does transfer energy from the battery to other components.
Voltage of a battery is measure of it's 'push' on the charges.
Components in a circuit resist the flow of charge. Bigger resistance = smaller current.
Together the battery, voltage and resistance detirmine the current in the circuit.
Total resistance of resistors in parallel is less than that of any single resistor - the group provides more loops for charges to flow around.
A voltmeter measures the potential difference between 2 points it's connected to.
Resistors in parallel have the same p.d. across each of them.
P.d. across resistors in series is proportonial to their resistance.
The power (energy/sec) transferred by an electric circuit is equal to 'current x voltage'.
A p.d. is induced across the ends of a wire/coil placed in a changing magnetic field.
Electromagnetic induction (transformer coursework)

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A wave is disturbance moving through a medium. The particles move but the medium doesn't move as a whole in the direction of the wave.
A wave carries energy and information through the medium.
The amplitude of a wave is the maximum disturbance of each particle of the medium as the wave passes.
The frequency is the number of waves produced/second by the source.
The wave speed is the speed at which each wave crest moves through the medium.
Amplitude and frequency depend on the source, wave speed depends on the medium.
Wave speed = frequency x wavelength
The bigger the frequency the smaller the wavelength.
Reflection - wave hits a barrier and bounces back off it.
Refraction - waves change their wavelength if they travel from one medium to another in which their speed is different.
Diffraction - like Pink Floyd album cover.
Interference - when two waves meet. If waves have the same frequency, an interference pattern is formed. In some places crests add to crests, forming bigger crests; in other places crests and troughs cancel each other out.

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Light behaves like a wave, showing diffraction and interference.
The electromagnetic 'family' of waves all travel through a vacuum at 300,000km/s.
Electromagnetic waves have different properties based on their frequency.
Radio, microwave, infrared, visible light, ultra violet, x-rays, gamma rays.
UV, x-rays and gamma rays are ionising - they can cause chemical changes in materials that absorb them.
Electromagnetic waves can be used to carry information. This is 'coded' on to a carrier waves, as changes in amplitude or frequency (analogue signals), or by pulsing the beam on and off very rapidly (digital signals).
Digital signals can be communicated more accurately, with less unwanted noise.

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