# Force & Pressure

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Force & Pressure

## 1. Pressure

### 1.2. When does the pressure increase?

1.2.1. When the force increases.

1.2.2. When the area decreases

### 1.4. When is low pressure needed?

1.4.1. When people or machines move on soft ground or snow.

### 1.5. When is high pressure needed?

1.5.1. Football shoes with spikes that need the grip to run.

## 2. what is a force?

### 2.3. What are the effects of a force?

2.3.1. Starts or stops a moving object

2.3.2. Change direction or speed of a moving object

2.3.3. Change shape or size of object

### 2.4. How can we measure a force?

2.4.1. Eg. Spring balances

2.4.1.1. 1. Extension

2.4.1.1.1. The spring stretches when a force pulls on it

2.4.1.2. 2. Compression

2.4.1.2.1. The spring compresses when a force pushes on it

### 2.5. Units of force

2.5.1. SI Unit: Newton

2.5.2. symbol: N

2.5.3. Named after English Scientist Sir Isaac Newton

## 3. Important Forces around us.

### 3.1. gravitational force

3.1.1. Exists between any two objects

3.1.2. Its the force that causes all objects to be attracted to Earth.

3.1.3. Weight

3.1.3.1. Gravitational force acting on object.

3.1.3.2. measure using a spring balance in newtons

3.1.3.3. The grater the force of gravity pulling an object, the greater the weight.

3.1.3.4. The force of gravity on Earth is greater than that of the moon. Therefore, we weigh more on Earth then on the moon.

### 3.2. magnetic force

3.2.1. It is the force exerted by a magnet on a magnetic material

3.2.2. A magnet has two poles.

3.2.2.1. North-seeking pole (N)

3.2.2.2. South-seeking pole (S)

3.2.2.3. Like poles repel and unlike poles attract

### 3.3. Frictional force

3.3.1. occurs when two moving objects are in contact

3.3.2. effects

3.3.2.1. Slows down and/or stops a moving object

3.3.2.2. produces more heat between rough surfaces

3.3.2.3. Produces heat

3.3.2.4. opposes motion

3.3.3. acts in the opposite direction

3.3.4. Useful or a problem?

3.3.4.1. How is it useful?

3.3.4.1.1. Gives us the grip to walk so we won't trip and fall easily

3.3.4.1.2. Holds a nail in the wall.

3.3.4.1.3. Friction between the wheel and the bicycle slows down the bicycle

3.3.4.2. A problem?

3.3.4.2.1. Wears away materials

3.3.4.2.2. Makes movement difficult

3.3.4.2.3. Produces heat

3.3.4.3. How can friction be reduced?

3.3.4.3.1. Lubricants

3.3.4.3.2. Ball bearings

3.3.4.3.3. Streamlined shapes