# Force & Pressure

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Force & Pressure

## 1. Calculating Pressure

### 1.1. A worked example

1.1.1. A hippopotamus weighs 20 000 N. It stands on one foot with an area of 5000 cm2 What is the pressure on the ground?

1.1.1.1. Solution

1.1.1.1.1. Pressure = Force / Area

1.1.1.1.2. 20 000 N / 5000 N/cm2 = 4 N/cm2

## 3. Pressure

### 3.1. What is Pressure?

3.1.1. Pressure is the force acting perpendicularly per unit area

### 3.2. How to increase Pressure?

3.2.1. Increase the force

3.2.2. decrease the area

3.2.2.1. Example

3.2.2.1.1. Cutting an object using a sharp knife

### 3.3. How to decrease/reduce Pressure

3.3.1. By increasing area

## 4. Important Forces

### 4.1. Magnetic Force

4.1.1. Uses of Magnetic Forces

4.1.1.1. The MAGLEV Train

4.1.1.1.1. Magnets in the track and train repel and lift the train a few centimetres above the track

4.1.1.1.2. As there is no contact between the track and vehicle, friction is reduced

4.1.1.1.3. This allows the train to move very fast (up to 500 km/h)

4.1.1.2. A magnet attracts steel pins. Picking up the steel pins with our hand will cause us to injure ourselves

4.1.1.3. A magnetic catch for the door of a cabinet keeps the fridge door shut tight

4.1.2. Bar magnet has two poles

4.1.2.1. The South Pole

4.1.2.2. The North Pole

4.1.3. Force exerted by a magnet on a magnetic material (e.g. iron and steel) or another magnet

4.1.4. Forces between magnets

4.1.4.1. Like poles repel : Magnets push away from one another

4.1.4.2. Unlike poles: Magnets pull towards each other

### 4.2. Frictional Force

4.2.1. Also called friction

4.2.2. Occurs When two moving surfaces are in contact

4.2.3. Effects of Frictional Force

4.2.3.1. Produces Heat

4.2.3.2. Slows down and/or stops a moving object

4.2.4. Useful effects of Frictional Force

4.2.4.1. Friction enables us to walk

4.2.4.2. Friction between the wheel and the brakes slows down the bicycle

4.2.4.3. Friction holds a nail in a wall

4.2.5. Negative effects of Friction

4.2.5.1. Makes movement more difficult

4.2.5.2. Wears away materials

4.2.5.3. Produces heat

4.2.6. Ways to reduce Friction

4.2.6.1. Using smooth surfaces

4.2.6.2. Using ball bearings

4.2.6.3. Lubrication

4.2.6.4. Streamlining

### 4.3. Gravitational Force

4.3.1. Also called gravity

4.3.2. Exists between any two objects

4.3.3. This is the force that causes all objects to be attracted to the Earth

4.3.3.1. Examples

4.3.3.1.1. A coconut falling from the sky

4.3.3.1.2. A ball coming down after being thrown skywards