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Physics Revision (Energy transfers (Current is a movement of electrons and…
Physics Revision
Energy transfers
Current is a movement of electrons and is the same everywhere in a series circuit. Current divides between loops in a parallel circuit, combines when loops meet, lights up bulbs and makes components work.
Around a charged object, the electric field affects other charged objects, causing them to be attracted or repelled. The field strength decreases with distance.
Fact: Two similarly charged objects repel, two differently charged objects attract.
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Charged up: When materials are rubbed together, electrons move from one surface to the other.
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Current: Flow of electric charge, in amperes (A).
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Gravity
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Mass and weight are different but related. Mass is a property of the object; weight depends upon mass but also on gravitational field strength.
Every object exerts a gravitational force on every other object. The force increases with mass and decreases with distance. Gravity holds planets and moons in orbit around larger bodies.
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Gravitational field strength, g: The force from gravity on 1 kg (N/kg).
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Speed
If the overall, resultant force on an object is non-zero, its motion changes and it slows down, speeds up or changes direction.
Use the formula: speed = distance (m)/time (s) or distance-time graphs, to calculate speed.
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A straight line on a distance-time graph shows constant speed, a curving line shows acceleration.
The higher the speed of an object, the shorter the time taken for a journey.
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Relative motion: Different observers judge speeds differently if they are in motion too, so an object�s speed is relative to the observer�s speed.
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FORCES
When the resultant force on an object is 0, it is in equilibrium and does not move, or remains at a constant speed in a straight line.
Sink or float?
Objects will sink and float depending on the amount of upthrust applied by the liquid, and the weight of the object. If the density of the object is more dense than the liquid it is in, then it will sink.
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Key words
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Linear relationship: When two variables are graphed and show a straight line which goes through the origin, and they can be called proportional.
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Resultant force: Single force which can replace all the forces acting on an object and have the same effect.
Friction: Force opposing motion which is caused by the interaction of surfaces moving over one another. It is called �drag� if one is a fluid.
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Pressure: The ratio of force to surface area, in N/m2, and how it causes stresses in solids.
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Waves
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The greater the amplitude of the waveform, the louder the sound
The greater the frequency, the higher the pitch
Facts
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The speed of sound in air is 330 m/s, a million times slower than light.
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Light waves can be absorbed, refracted or reflected.
Key words for waves
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Volume: How loud or quiet a sound is, in decibels (dB).
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Amplitude: The maximum amount of vibration, measured from the middle position of the wave, in metres.
Wavelength: Distance between two corresponding points on a wave, in metres.
Frequency: The number of waves produced in one second, in hertz.
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Oscilloscope: Device able to view patterns of sound waves that have been turned into electrical signals.
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Normal line: From which angles are measured, at right angles to the surface.
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