# Force and Pressure

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Force and Pressure

## 3. How can we measure a force?

### 3.1. Using a force-meter

3.1.1. Spring-balances

3.1.1.1. Extension spring balance

3.1.1.1.1. Spring stretches when a force pulls on it

3.1.1.2. Compression spring balance

3.1.1.2.1. Spring is compressed when a force acts on it

## 4. What are the important forces around us?

### 4.1. Frictional Force

4.1.1. Occurs whenever there are two moving surfaces in contact

4.1.2. Slows down and stops a moving object

4.1.3. Produces heat

4.1.4. Friction can be useful

4.1.4.1. Friction holds a nail in the wall

4.1.4.2. Friction between the wheel and the brakes slow down the bicycle

4.1.4.3. Friction between our feet and the ground gives us the grip needed to walk and run

4.1.5. Friction can be a problem

4.1.5.1. Makes movement more difficult

4.1.5.2. Wears away materials

4.1.6. Ways to reduce Friction

4.1.6.1. Use smooth surfaces

4.1.6.2. Ball bearings

4.1.6.3. Lubrication

4.1.6.4. Streamlining

### 4.2. Magnetic Force

4.2.1. Magnets can attract objects made of iron and steel

4.2.2. Magnets exert a force called magnetic force

4.2.3. Examples of Magnetic Force

4.2.3.1. Magnetic catch for the door of a cabinet keeps the door shut

4.2.3.2. The needle of a compass is a small magnet. A compass is used to give directions

4.2.3.3. A magnet attracts steel pin. Picking up the pins ourselves may injure our fingers

4.2.3.4. A crane uses a powerful magnet to lift iron and steel objects

4.2.4. Forces between magnets

4.2.4.1. Magnets can exert a force on other magnets

4.2.4.2. Bar magnets each have a North and South pole

4.2.4.3. Like poles repel (Push)

4.2.4.4. Unlike poles attract (Pull)

### 4.3. Gravitational Force

4.3.1. A force that pulls objects towards the Earth

4.3.2. Exists between any two objects

### 4.4. Weight

4.4.1. Weight of an object depends on the force of gravity pulling on that object

4.4.2. The greater the force of gravity pulling on an object, the heavier the object

## 5. What is Pressure?

### 5.4. Increasing Pressure by reducing Area

5.4.1. For the same force, when a smaller surface is in contact with an object, the pressure exerted on the object is higher

### 5.5. Reducing Pressure by increasing Area

5.5.1. Low pressures are needed when people or machines move on soft ground or snow