3 - EoY Physics Revision
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Distance is measured in metres. Time is measured in seconds.
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Speed is measured in metres per second.
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Distance travelled = average speed x time taken
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A distance - time graph shows how far an object has moved in a given time. The gradient (slope) of a distance- time graph tells us the speed. A steeper slope means a higher speed.
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If an object is getting faster or slower (accelerating), its speed at any particular time can be determined by drawing a tangent and measuring the gradient of the distance–time graph at that time.
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The speed that a person can walk, run or cycle depends on their age and fitness, the terrain, and distance travelled.
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These speeds often change but typical values may be taken as:
walking ≈ 1.5 m/s
running ≈ 3 m/s
cycling ≈ 6 m/s
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A vector quantity is one where direction matters as well as its size (magnitude). Force, velocity, and displacement are examples of vector quantities.
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A scalar quantity is one where only magnitude matters. Mass, energy, and temperature are examples of scalar quantities.
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Energy is transferred between stores
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This can be as kinetic, gravitational, chemical, elastic, magnetic, electrostatic, nuclear, and thermal stores of different objects
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Energy can be transferred mechanically, electrically, by heating, by radiation (light and sound)
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The amount of energy transferred away from one store is the same as the energy gained by other stores.
Efficiency tells us the fraction of the energy input that is transferred usefully (to a store we want).
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Useful energy output = efficiency x Total energy input
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Energy that is not transferred to the store we want is said to be ‘wasted’ or ‘dissipated’. This can be reduced by lubricating machinery or using thermal insulation.
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A measurement can be improved by repeating it and finding a meaning.
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We can also improve data quality from a scale by reducing parallax; we make our reading with our eyes perpendicular to the scale.
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The independent variable is what we purposefully alter in an investigation.
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The dependent variable is what changes because of what we have altered.
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Control variables are things that would alter the dependent variable unless they were kept the same throughout the investigation.
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A Sankey diagram shows the energy transfers for a device.
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These are scale diagrams, where the widths of the arrows represent the amount of energy transferred to a particular store.
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An atom is the smallest piece of an element, having a radius of about 1 x 10-10 metres.
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Atoms have a tiny nucleus made of particles called protons and neutrons. The nucleus is surrounded by a cloud of particles called electrons.
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The atomic number tells us the number of protons in the nucleus. The mass number
tells us the total number of protons and neutrons in the nucleus.
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The atomic number tells us which element we are dealing with. Isotopes are different versions of an element; two isotopes of an element have the same number of protons, but a different number of neutrons.
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Some isotopes are unstable, which means they break apart. We call them radioisotopes. They can decay by emitting nuclear radiation such as alpha (α) particles, beta (β) particles, gamma (γ) rays, and neutrons (n).
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If a nucleus emits an alpha particle, the remaining nucleus (daughter nucleus) has two fewer protons and two fewer neutrons.
If a nucleus emits a beta particle, the remaining nucleus (daughter nucleus) has one fewer neutron and one more proton.
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We can detect nuclear radiation using photographic film or a Geiger–Müller detector
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Radiation is ionising if it creates ions when it moves through a substance by removing electrons from the atoms of the substance.
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When ions are made, energy is transferred from the radiation to the substance. The radiation is eventually absorbed. Strongly ionising radiation is absorbed more easily than weakly ionising radiation.
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| Properties: | What is it? | Required to absorb it | How strongly ionising? |
|---|---|---|---|
| Alpha particle | 2 protons and 2 neutrons | Paper, 10cm of air | Very - creates ions easily. |
| Beta particle | An electron | About 5 mm of aluminium | Moderately |
| Gamma ray | An electromagnetic wave | A few cm of lead | Weakly - few ions made. |
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There is a small amount of nuclear radiation around us all of the time from natural and human made sources. This is known as background radiation. The main sources are radon gas, cosmic rays, medical exposure, nuclear waste, and nuclear weapons testing.
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