# Pressure and Force

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Pressure and Force

## 1. Force

### 1.2. Effects

1.2.1. Change the speed of a moving object by either increasing or decreasing its speed

1.2.2. Change the shape or size of an object

1.2.3. Start a stationary object or stop a moving object

1.2.4. Change the direction of a moving object

### 1.4. Important forces around us

1.4.1. Frictional force (friction)

1.4.1.1. occurs whenever two moving surfaces come in contact

1.4.1.2. Slows down and stops a moving object

1.4.1.3. produces heat

1.4.1.4. Negative effects of friction

1.4.1.4.1. may cause thing to wear and tear

1.4.1.4.2. makes movement more difficult

1.4.1.5. Reducing friction

1.4.1.5.1. make surface smoother by polishing

1.4.1.5.2. lubricate the object

1.4.1.5.3. use ball bearings

1.4.1.5.4. Streamlining

1.4.1.6. Useful effects of friction

1.4.1.6.1. enable us to walk

1.4.1.6.2. enable us to hold things

1.4.2. Magnetic Force

1.4.2.1. Force exerted by a magnet on another magnet or another magnetic material

1.4.2.2. Uses of magnetic force

1.4.2.2.1. magnetic catch for the door of a cabinet. it keeps the door shut

1.4.2.2.2. needle of a compass is a small magnet. it is used to give directions

1.4.2.3. forces between magnets

1.4.2.3.1. Like poles repel

1.4.2.3.2. unlike poles attract

1.4.3. Gravitational force (gravity)

1.4.3.1. a force that pulls the object toward the Earth

1.4.3.2. Weight

1.4.3.2.1. depends on force of gravity pulling on object

1.4.3.2.2. measured using a spring balance

1.4.3.2.3. measured in Newtons

## 2. Pressure

### 2.3. Calculating force: Force (Newton/N) divided by area

2.3.1. Example: An elephant weighs 35000 N. It stands on one foot with an area of 1000cm2. Find the pressure on the ground .

### 2.5. Increasing pressure

2.5.1. reducing area

2.5.1.1. for the same force, when a smaller surface is in contact with an object, the pressure is higher

2.5.1.1.1. Examples - A sharp knife can cut things easily. Blunt knife cuts less easier.

### 2.6. reducing pressure

2.6.1. Low pressures are needed when people or machines move on soft ground (eg. sand) or snow so that they will not sink

2.6.1.1. Examples: - A camel's legs are flat and lrge to prevent it from sinking in the sand

2.6.1.2. Skis have a large surface area so that it wont sink in the snow

2.6.2. Increase area