## 1. Question: You can push a drawing pin into a piece of wood- but you cannot push your finger into the wood even if you exert a larger force. Why? What is the difference between a sharp knife and a blunt knife?

### 1.1. Answer: The difference in each case is a difference of area- the point of the drawing pin and the edge of the sharp knife have a small area. A force acting over a small area gives a large pressure. Pressure is force per unit area, or pressure= force (in newtons)/ area (in square metres). Its unitis newtons per square metre(N/m2). The unit is also called the Pascal (Pa), named after Blaise Pascal, who investigated air pressure.

## 2. Making the force the same but increasing the area also increases pressure.

## 3. Pressure decreases when force decreases or when area increases.

## 4. Pressure increases when force increases or when area decreases.

## 5. Pressure is simply the force exerted per unit area.

## 6. Pressure depends on force and area.

## 7. Given that the surface area of the elephant foot is 100 cm2 and the force exerted is 30,000n. Calculate the pressure exerted by the elephants foot. The answer is 3,000,000.

## 8. Frictional force, electromagnetic force, gravitational force

### 8.1. Frictional force occurs when two contacts rub against each other.

8.1.1. Friction moves to the oppsite direction of motion.

8.1.1.1. Lubricants like ball bearings or grease can be used in order to reduce friction.

8.1.1.1.1. Force can be a push or pull. It is measured by a spring balance.