CCEA GCSE Physics

GCSE · CCEAPhysics33 篇笔记个文件夹，140 KB

cookie 制作的复习笔记，共 33 篇，分为 11 个章节，按照课程主题编排。

Notes for CCEA GCSE Physics (specification for first teaching 2017), in folders for each of its content areas in the specification's order, from motion through to space physics, with the prescribed practicals in the topics they belong to and a final folder on practical skills. Higher-tier content is marked where it sits. Delete any folder or note your tier does not need once the notes are yours.

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内容

Motion
- Speed, velocity and acceleration4 KB
- Motion graphs5 KB
Force
- Forces and Newton's laws5 KB
- Hooke's law and pressure4 KB
- Moments and centre of gravity6 KB
Density and kinetic theory
- Density and the states of matter5 KB
Energy
- Energy forms, conservation and efficiency3 KB
- Energy resources3 KB
- Work, power and mechanical energy5 KB
- Heat transfer5 KB
Atomic and nuclear physics
- Atomic structure and the nucleus4 KB
- Radioactive decay and radiation4 KB
- Half-life, dangers and uses of radioactivity5 KB
- Nuclear fission and fusion4 KB
Waves
- Wave properties5 KB
- Echoes, sonar, radar and the electromagnetic spectrum4 KB
Light
- Reflection, refraction and dispersion5 KB
- Critical angle and total internal reflection4 KB
- Lenses and the eye4 KB
Electricity
- Charge, current and circuit diagrams4 KB
- Ohm's law and V-I graphs3 KB
- Series and parallel circuits4 KB
- Factors affecting resistance3 KB
- Electrical energy, power and cost3 KB
- Mains electricity, plugs and switching4 KB
Magnetism and electromagnetism
- Magnetic fields and electromagnets4 KB
- Force on a current and the electric motor3 KB
- Induction, generators and transformers5 KB
Space physics
- The Solar System and satellites4 KB
- Stars, life cycles and black holes3 KB
- The Universe and space exploration5 KB
Practical skills
- Planning and carrying out an investigation5 KB
- Analysing data and drawing conclusions6 KB

第一篇笔记

Motion / Speed, velocity and acceleration

Average speed

Speed says how quickly an object covers distance. Distance is measured in metres (m), time in seconds (s) and speed in metres per second (m/s). Over a whole trip the speed usually changes, so what is calculated is the average speed:

\text{average speed} = \frac{\text{distance moved}}{\text{time taken}}

A cyclist who covers 1 800 m in 300 s has an average speed of $1800 \div 300 = 6.0$ m/s.

If an object speeds up or slows down at a steady rate, its average speed can also be found from the speeds at the start and the end of the motion:

\text{average speed} = \frac{\text{initial speed} + \text{final speed}}{2}

A train slows steadily from 30 m/s to 10 m/s. Its average speed is $(30 + 10) \div 2 = 20$ m/s, so in 50 s it moves $20 \times 50 = 1000$ m. The equation only works when the change of speed is steady, because it treats the speed as sitting halfway between the two values.

Rate of change of speed

The rate of change of speed says how quickly the speed is going up or down. It is measured in metres per second squared (m/s²), because it is a change of speed in m/s divided by a time in s.

\text{rate of change of speed} = \frac{\text{final speed} - \text{initial speed}}{\text{time taken}}

A car moves off from rest and reaches 24 m/s after 8.0 s.

\begin{aligned} \text{rate of change of speed} &= \frac{24 - 0}{8.0} \\ &= 3.0\ \mathrm{m/s^2} \end{aligned}

This means its speed rises by 3.0 m/s in every second. A negative answer means the object is slowing down. The equation can be rearranged to find the final speed or the time taken: the final speed is the initial speed plus the rate of change of speed multiplied by the time.

Scalars and vectors

Higher tier only

A scalar is a quantity that has size but no direction. A vector is a quantity that depends on direction as well as size. Distance, speed and the rate of change of speed are scalars. Their vector partners are displacement, velocity and acceleration, and the units are the same: metres, metres per second and metres per second squared.

Displacement is the distance moved in a stated direction, measured in a straight line from the starting point. A runner who completes one lap of a 400 m track has gone a distance of 400 m but ends up back at the start, so the displacement is zero. Velocity is the rate of change of displacement, so it has a direction too. A car driving round a circular track at a steady 30 m/s has a constant speed but a velocity that keeps changing, because the direction keeps changing. A change of velocity is an acceleration, so the car is accelerating even though its speed stays the same.

Velocity and acceleration equations

Higher tier only. For motion in one direction the equations mirror the ones for speed.

\text{average velocity} = \frac{\text{displacement}}{\text{time}}

\text{average velocity} = \frac{\text{initial velocity} + \text{final velocity}}{2}

\text{acceleration} = \frac{\text{final velocity} - \text{initial velocity}}{\text{time taken}}

Acceleration is measured in m/s². A cyclist travelling east at 4.0 m/s speeds up to 10.0 m/s over 3.0 s. The acceleration is $(10.0 - 4.0) \div 3.0 = 2.0$ m/s² east, and the average velocity is $(4.0 + 10.0) \div 2 = 7.0$ m/s east, so the displacement is $7.0 \times 3.0 = 21$ m east.

Only motion in a straight line is set in calculations, so a direction can be shown with a sign: one direction is positive and the opposite direction is negative.

Retardation

Higher tier only. Negative acceleration, where an object's velocity decreases in the positive direction, is called retardation. A car moving at 20 m/s that brakes to rest in 5.0 s has an acceleration of $(0 - 20) \div 5.0 = -4.0$ m/s², a retardation of 4.0 m/s².

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