Physics.

GCSE Physics

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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 Circuits.

• 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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The Wave Model of Radiation. Part 1.

• 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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The Wave Model of Radiation. Part 2.

• 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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