### Wave Speed

Wave speed is given in meters per second (the number of waves that pass per second). Wavelength is measured in meters and frequency is measured in hertz (Hz), or number of waves per second.

### Force on a Spring

When a force acts on a spring it is stretched or compressed, its length will changes by an amount e from its original length.

### Force, Mass and Acceleration

An object of constant mass accelerates in proportion to the force applied.

### Elastic Potential Energy

Stretching or squashing an object can transfer energy into its elastic potential energy store.

### Forces and Work Done

The unit for work done is the joule (J), or Newton meter (N-m). One joule is equal to the amount of work that is done when 1 N of force moves an object over a distance of 1 m.

### Momentum

All moving objects have momentum. Forces can cause changes in momentum. The total momentum in a collision or explosion is conserved and stays the same. Car safety features absorb energy involved in a crash they slow down the collision thus reducing the force of impact.

### Wave Period

The period of a wave is the time it takes to complete one cycle. The unit for a wave period is seconds, and it is inversely proportional to the frequency of a wave, which is the number of cycles of a wave that occur in one second.

### The Motor Effect

A current-carrying wire or coil can exert a force on a permanent magnet. The force increases if the strength of the magnetic field and/or current increases. This is called the motor effect.

### Acceleration

Acceleration is how quickly the velocity is changing whether it be speed, direction or both. Acceleration is a measure of how quickly the velocity of an object is changing.

### Speed

Speed is how fast an object is moving in no given direction. Velocity is how fast an object is moving in a given direction. In physics, you can calculate the average speed by taking the total distance travelled and dividing it by the total time required to travel that distance.

### Weight on the Moon

Weight is the force acting on an object due to gravity. The weight of an object is defined as the force of gravity on the object and can be calculated as the mass times the acceleration due to gravity.

### Weight on Earth

Weight is the force acting on an object due to gravity. The weight of an object can be defined as the force of gravity on the object. Since the weight is a force, its unit is the Newton.