# Velocity

## Key Stage 3

### Meaning

Velocity is very similar to speed but it includes the direction an object is moving.

## Key Stage 4

### Meaning

Velocity is a vector quantity describing the speed and direction of a moving object.

Velocity is a scalar because it has magnitude and direction.
The SI Unit for the magnitude of velocity is metres per second (m/s).
Velocity is different from its scalar counterpart 'speed' because speed does not include the direction of travel.
The velocity of an object can change while the speed remains constant.

### Equation

Velocity = (Displacement) / (time)

$$v = \frac{s}{t}$$

Where

$$v$$ = Velocity of the object.

$$s$$ = The displacement between the starting point and end point of a journey.

$$t$$ = The time taken between the two points.

### Example Calculations

 A wave travels 1000m in a time of 12.5s. Calculate the magnitude of the velocity of the wave correct to two significant figures. The Moon is approximately 390,000km away from the Earth. It takes a Radio Wave 1.3 seconds to travel that distance. Calculate the magnitude of the velocity of the Radio Wave correct to two significant figures. An alpha particle can travels around 6cm from a source taking 4.0ns before colliding with an air molecule. Calculate the magnitude of its velocity on this journey correct to two significant figures. 1. State the known quantities s = 1000m t = 12.5s 1. State the known quantities s = 390,000km = 390,000,000m t = 1.3s 1. State the known quantities s = 6cm = 0.06m t = 4.0ns = 4.0 x 10-9m 2. Substitute the numbers into the equation and solve. $$v = \frac{s}{t}$$ $$v = \frac{1000}{12.5}$$ $$v = 80m/s$$ 2. Substitute the numbers into the equation and solve. $$v = \frac{s}{t}$$ $$v = \frac{390000000}{1.3}$$ $$v = 300,000,000m/s$$ 2. Substitute the numbers into the equation and solve. $$v = \frac{s}{t}$$ $$v = \frac{0.06}{4.0 \times 10^{-9}}$$ $$v = 15,000,000m/s$$