Pressure

Pressure in physics tells us about the concentration of a force. Imagine sitting on a chair. Ah! Relax. It's rather different if someone leaves a drawing pin on the seat!  In the first case your weight (gravity force)  is spread out over the whole of the area you press on. When the pin is there you put the same force onto a tiny area. This increases the pressure and the pin sinks into you. 

Many things are designed to have a high or a low pressure when used. A garden fork is made to have a high pressure. The ends of the prongs are sharp. This makes a high pressure so when you press on it it will sink into the earth. The drawing pin is another example the sharp end makes a high pressure so it will sink into display boards. The other end has a bigger area. This gives a low pressure so it will not think into your thumb. Snow shoes are also designed to have a low pressure they spread out your weight so you don't sink too far into the snow.

To calculate the pressure made by something you divide the force by the area it is exerted (made) on. So

Pressure=Force/area

Forces are measured in Newtons and areas are measured in cm2 (centimetres squared) or m2. This means pressure is measured in N\cm2 (Force divided by area) or N\m2 which is also called a Pascal (Pa). Check your bicycle tyres they will probably have this but also lb\in2 or pounds per square inch.