Imagine what it is like to be an army tank driver. You must be very alert. You must be able to react quickly when under fire and drive the vehicle carefully through muddy fields or shifting sands. Tanks can weight 70 ton, so why do they not get stuck in mud or sands? The answer lies in how their pressure is distributed over the ground. Instead of wheels, tanks use caterpillar tracks.

The gun on top of a tank can move around in a complete circle as well as up and down. This is very important when you are being fired at from all directions. The gun moves using a system called hydraulics. This uses a liquid to transfer pressure from one part of the tank to another.

Concorde used to travel at twice the speed of sound. It had to accelerate quickly at take off. Parachute teams need to understand air resistance to put on their displays. Pneumatic tires make traveling over bumpy ground more comfortable. Some scientists think that levers were used to move the great stones at Stonehenge.

Speed cameras calculate the speed of vehicles to catch speeding drivers. The flash from a roadside speed camera is bad news if a driver sees it in their cars rear view mirror. It means that they have been caught speeding and will be fined and get points on their drivers license. Speed cameras calculate the speed of a vehicle at a particular point in time. To calculate a cars speed over a whole journey, you can use a distance-time graph to model speed.

Bruce is a racing car driver. He needs to know how fast he is going at different places around the racetrack. A lot of data is collected by computers in his racing car. Bruce can compare his data with data collected from other drivers to work out where he is fastest and where other drivers are the fastest. The data can be used to produce a distance-time graph. Scientists use graphs to make data easier to understand.

The slope or gradient of a distance-time graph shows the speed. The steeper the gradient, the faster the speed. If an object is not moving, the line on the distance – time graph is horizontal.

Scientists also use speed-time graphs to model speed. On a speed-time graph, steady speed is shown by a horizontal line. When a driver speeds up, the graphs gradient is upwards. Scientists call speeding up acceleration. When the driver slows down, the graphs gradient is downwards. Slowing down is called deceleration. Objects speed up and slow down because the forces acting on them are unbalanced.