# Force and Pressure

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Force and Pressure

## 1. Force

### 1.1. What is a force?

1.1.1. A push of a pull

1.1.1.1. eg

1.1.1.1.1. Lifting

1.1.1.1.2. Bending

1.1.1.1.3. Stretching

1.1.1.1.4. Twisting

1.1.1.1.5. Squeezing

1.1.2. Exerted when 1 thing interacts with another.

### 1.2. Effects

1.2.1. Make stationary object move

1.2.2. Stop moving object

1.2.3. Change

1.2.3.1. Speed of moving object

1.2.3.2. Direction of moving object

1.2.3.3. Shape of object

1.2.3.4. Size of object

1.3.1. SI unit

1.3.1.1. Newton

1.3.2. Symbol

1.3.2.1. N

### 1.4. Types

1.4.1. Frictional force

1.4.1.1. Occurs when 2 moving objects in contact

1.4.1.2. Opposes and slows down motion

1.4.1.3. Effects

1.4.1.3.1. Useful

1.4.1.3.2. Negative

1.4.1.4. Reduce friction

1.4.1.4.1. Smooth surfaces

1.4.1.4.2. Ball bearings

1.4.1.4.3. Lubrication

1.4.1.4.4. Streamlining

1.4.2. Magnetic Force

1.4.2.1. Force exerted by magnet on

1.4.2.1.1. magnetic material

1.4.2.1.2. another magnet

1.4.2.2. Forces between magnets

1.4.2.2.1. Like poles repel

1.4.2.2.2. Unlike poles attract

1.4.2.3. Uses

1.4.2.3.1. Magnet catch for door of cabinet

1.4.2.3.2. Needle of compass is a small magnet

1.4.2.3.3. Magnet attracts steel pins

1.4.2.3.4. Crane uses powerful magnets to lift iron & steel objects

1.4.3. Gravitational force

1.4.3.1. Force that pulls object towards Earth

1.4.3.1.1. Exist between any 2 objects

1.4.3.2. Weight

1.4.3.2.1. Depends on force of gravity pulling on object

1.4.3.2.2. Measured

### 1.5. Measuring instruments

1.5.1. Spring balance

1.5.1.1. Extension

1.5.1.1.1. stretches when a force pulls it

1.5.1.1.2. force ↑, spring stretches ↑

1.5.1.2. Compression

1.5.1.2.1. compresses when a force pushes it

1.5.1.2.2. force ↑, spring compresses ↑

## 2. Pressure

### 2.2. SI unit

2.2.1. Pascal (Pa)

### 2.3. Calculating pressure

2.3.1. Force(N) divided by Area

### 2.4. Increasing pressure

2.4.1. by reducing area

2.4.1.1. For same force, when smaller surface in contact with object, pressure is higher

2.4.1.1.1. Eg

### 2.5. Reducing pressure

2.5.1. by increasing area

### 2.6. Low pressures are needed when people or machines move on soft ground or snow, so that they will not sink

2.6.1. Eg

2.6.1.1. Skis have large surface area to prevent the skier from sinking into the snow

2.6.1.2. Camel has large, flat feet,to prevent it from sinking into the desert sand

2.6.1.3. Excavator has wheels called caterpillar tracks, which has large area to spread its weight over large area, to prevent it to sink easily into the mud/sand