In this topic we are learning to: z Measure and calculate pressures. z Outline how pressure varies in liquids and gases. z Explain what is meant by atmospheric pressure.
When you cut bread, push a thumbtack into wood or even stand on the floor, you apply a force. This force is applied over an area. The smaller the area, the more concentrated the force will be.
The amount of force over a unit of area is known as pressure. Pressure is calculated using the following equation:
Pressure = Pressure
Based on what you know, try to answer the following questions in groups: 1. Why do we cut bread with the sharp side of a knife? 2. You can push a thumbtack into a piece of wood, but cannot push your thumb into the wood. Why? 3. Why do tractors have very wide tyres?
Depending on the situation, you may want a high or a low pressure. For example:
z Snowshoes increase the area a person’s body weight is spread over. This reduces pressure, preventing the person sinking into the snow.
Fig. 17.6.1
Snowshoes and running shoes distribute body weight differently
z The spikes on running shoes concentrate body weight over a smaller area. This increases pressure, making the shoes sink into the track and increasing the runner’s grip.
Force applied (N) Area it is applied over (m2) Unit of pressure = N/m2
