1. Pressure
1.1. SI Unit
1.1.1. Newton per square centimeter or Pascal
1.2. Definition
1.2.1. Force per unit area
2. Forces
2.1. Effects of forces
2.1.1. Set a rest object into motion
2.1.2. Change direction in which the object was moving
2.1.3. Change the speed of an object
2.1.4. Change the size and shape of an object
2.2. Definition
2.2.1. A force is a push or a pull
2.3. Measurement of forces
2.3.1. SI Unit
2.3.1.1. Newton
2.3.1.1.1. One Newton is the force of gravity acting on a mass of about 100g at sea level.
2.3.2. How can forces be measured?
2.3.2.1. Force meters are used to measure forces
2.3.2.1.1. Extension Spring Balances
2.3.2.1.2. Compression Spring Balances
3. Gravity
3.1. Definition
3.1.1. Force that pulls objects towards Earth
3.2. Weight
3.2.1. Definiton
3.2.1.1. The force of gravity acting on an object by the Earth.
3.2.2. Formula
3.2.2.1. Weight = Mass x Gravitational acceleration
3.2.3. Weight is not mass. Mass is the amount of matter in an object.
3.2.4. Weight decreases with increasing distance from the centre of the Earth.
4. Friction
4.1. What is friction?
4.1.1. Friction is a force that is produced when two surfaces in contact with each other rub against each other
4.1.2. It slows down or stops a motion of an object
4.1.3. It acts in an opposite direction
4.1.4. Produces heat
4.2. Reducing friction
4.2.1. Lubricants
4.2.2. Rollers, Ball bearings, wheels
4.2.3. Polishing the surfaces
4.3. Advantages of friction
4.3.1. Friction helps vehicles slow down when brakes are applied
4.3.2. Friction prevents slipping during movement
4.3.3. Friction facilitates gripping
4.4. Disadvantages of friction
4.4.1. Friction slows down movement of an object
4.4.2. Friction converts useful energy into unwanted heat in machines
4.4.3. Soles of our shoes wear out after some time due to friction
4.4.4. Tyres of cars have to be replaced regularly due to the friction between the tyres and ground