- 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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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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