# Notes

## Refraction of light

Refraction is the bending of light when it enters a different medium The diagram below shows how a ray of light passes through a glass block

## Reflection in plane mirrors

The laws of reflection When a ray of light strikes a mirror, it is reflected. The incoming ray is called the incidence ray, the outgoing ray is called the reflected ray, and the line perpendicular to the mirror is called the normal. The mirror in this case it is a...

## Features of light

light is a form of radiation This means that light radiates (spreads out) from its source. In a diagram lines called rays are used to show which way light is going light travels in straight lines We can see this if we look at sun beams or laser beams light...

## Speed of sound and echoes

The speed of sound Is about 330m/s in air, which is slower than the Concorde (a supersonic turbo passenger jet) but about four times faster than a racing car. Variables affect the speed of sound The speed of sound depends on temperature of the air for example the...

## Light and shade

To see something, light has to enter the eye. The sun, lamps, lasers all emit (send out) their own light (they are luminous) however, most objects are non-luminous you can only see them because of day light that bounces of them. They reflect light and some of that...

## Frequency and pitch

Pitch is the frequency of the wave, a high frequency has a high pitch and a low frequency has a low pitch

## Wave theory

Periodic motion Is motion of an object that regularly repeats – the object returns to a given position after a fixed time interval Describing oscillatory motion 1 oscillation: is the movement of an object from a given position to another and back Period: is the time...

## Ways to generate electricity

Thermal power Chemical energy (fuel) – thermal energy (fuel burner) – thermal energy (steam) – kinetic energy (turbine) – kinetic (generator) – electrical energy (electricity) Solar power Light energy (sun) – electrical energy (electricity) Wind power Light energy...

## Friction and braking

Friction: the force that tries to stop materials sliding across each other. Sometimes friction is reduced by ball or roller bearings on wheels, oil or grease to make the surface slippery. Static and dynamic friction When the block is pulled gently, friction stops it...

## Stopping distance

In an emergency, the driver of a car may have to react quickly and apply the brakes. The cars’ stopping distance is the sum of (thinking distance + braking distance). Stopping distance = thinking distance + braking distance. Thinking distance: how far the car travels...

## Efficiency and power

Efficiency Efficiency: how much useful energy something makes. Efficiency = useful energy output/ total energy input Efficiency is measured as a percentage Example Power Power: the amount of work that can be done in a period of time. The faster work is done the...

## Movement energy

Kinetic energy: Energy due to motion (all moving objects have kinetic energy) Thermal energy: energy due to heat making the particles more energetic (making them vibrate faster)

## Potential energy

Gravitational potential energy: energy due to the effects of gravity on an object (the higher the object is the more gravitational potential energy it has) Nuclear energy: energy due to the re-arrangement of particles or the splitting of the atoms’ nucleus Elastic...

Light energy: energy due to particles giving out (releasing) energy (this is also a form of radiated energy Sound energy: energy due to the vibrations of an object moving the particles of air in front of it (this is a form of radiated energy it travels in the form of...

## Force, weight and gravity

Gravitational force: the downward pull from the earth acting on an object. The features of gravitational force are: All masses attract each other The greater the masses the stronger the force The closer the masses the stronger the force Gravitational field: the field...

## Action and reaction

Every action has an equal and opposite reaction When a force acts on the earth the earth moves but its movement is too small to see Hooke’s law if something is bent slightly and you release it goes back to its original shape materials like this are called elastic  in...

## Energy

Materials are made up of atoms (particles) or molecules (groups of atoms) these are continuously moving (vibrating), if the material is heated the atoms move faster so the material has more energy. Energy is measured in joules

## Pressure

Pressure = force/area Pressure has Inverse proportion which means The higher the surface area the lower the pressure 1Pascal (pa) = 1n/m^2 1kpa = 1000pa

## Speed, velocity and acceleration

Speed Speed: the distance travelled between two points usually measured in m/s (meters per second). Average speed = distance/time. Velocity Velocity: the speed of an object and its direction. For direction you can use words such as forward, backward, left, right and...

## Work

Work: whenever a force makes something move (the greater the force the more distance move the greater the work). Work is measured in joules (j). 1j of work is done when 1n move an object 1m. Work is calculated by the formula. Work done = force x distance moved in the...

## Units

Speed = m/s (meters per second) Acceleration = m/s^2 (meters per second squared) Gravity = m/s (meters per second) (free fall), M/s^2 (meters per second squared) (acceleration due to gravity), N/kg (newtons per kilogram) (weight)  Resultant force = N (newtons)...

## Free Fall

Free fall: where something is falling with the effects of gravity and air resistance acting on it. Gravity (g) = 10m/s^2 (or 9.8m/s^2 to be more precise). . G (gravity) =acceleration of free fall. . To measure g the formula is Gravity = height of the fall x2/ time^2...

## Force, mass and acceleration

Inertia: the force it takes to move an object at (to make it go slower, faster or in a different direction), the more mass the object has the more inertia it has (inertia happens in all cases of motion, at rest, while moving and changing direction). Resultant force:...