# Forces and Pressure

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Forces and Pressure

1.2.1. newton(N)

## 3. measuring force

### 3.1. force meter

3.1.1. spring balance

3.1.1.1. extension spring balance

3.1.1.2. compression spring balace

## 4. some types of forces

### 4.1. frictional force

4.1.1. two moving surfaces are in contact

4.1.1.1. opposes motion

4.1.2. useful

4.1.2.1. hold two things together

4.1.2.2. slow things down when you brake

4.1.2.2.1. bicycle

4.1.2.2.2. car

4.1.2.3. soles on shoes prevent you from slipping

4.1.3. problem:(

4.1.3.1. cause wear and tear

4.1.3.2. cause the soles on our shoes to wear out

4.1.4. ways to reduce friction

4.1.4.1. smooth surfaces

4.1.4.2. ball bearings

4.1.4.3. lubrication

4.1.4.4. streamlined shape

### 4.2. magnetic force

4.2.1. a force that a magnet exerts

4.2.1.1.1. iron

4.2.1.1.2. steel

4.2.2. uses

4.2.2.1. needle of compass

4.2.2.1.1. give direction

4.2.2.2. keep the refrigerator door shut

4.2.3. forces between magnet

4.2.3.1. North-seeking pole(N)

4.2.3.2. South-seeking pole(S)

4.2.3.3. Like poles repel

4.2.3.4. Unlike poles attract

4.2.4. Maglev train

4.2.4.1. magnet in the track and train repel and lift the train a few centimetres above the the track

4.2.4.2. reduce friction

### 4.3. Gravitational force

4.3.1. pulls object towards earth

4.3.2. Weight

4.3.2.1. the force of gravity pulling on that object

## 5. pressure

### 5.2. pressure increase

5.2.1. area decrease

5.2.2. force increase

### 5.3. soft ground or snow

5.3.1. low pressure is needed

5.3.2. require larger area

5.3.3. so people or things won't sink

### 5.4. calculate pressure

5.4.1. Force/Area

5.4.2. unit of force

5.4.2.1. Newton(N)

5.4.3. if the unit area is (cm2) then the unit of pressure is (N/cm2)

5.4.4. if the unit of area is (m2) then the unit of pressure is (N/m2) this unit is also called pascal(pa) where 1 Pa=1N/m2

### 5.5. S1 unit

5.5.1. Pascal(Pa)