1. WEIGHT
1.1. The force of gravity acting on an object by the Earth
1.2. All objects on Earth have weight
1.3. Objects with bigger masses will have greater weights.
1.4. can be measured with a force meter
1.5. decreases with increasing distance from the centre of the Earth
1.5.1. a man has smaller weight when he is at the top of a tall mountain compared with when he is at sea level
1.6. Our weight on the Moon is about one-sixth of that on the Earth
1.7. The stronger the gravitational pull, the greaer the weight of an object
1.8. Weight (W) = Mass (m) x Gravitational acceleration (g)
2. Kinds of forces
2.1. Pushing
2.2. Pulling
2.3. Bending
2.4. Twisting
2.5. Wringing - a combination of push or pull
3. Pressure
3.1. the force acting per unit area
3.1.1. the bigger the force, the greater the pressure exerted
3.1.2. the smaller the contact area, the greater the pressure
3.2. SI unit is Newton per square meter, also known as Pascal (Pa)
3.3. can be increased by reducing the contact area
3.3.1. eg. a sharp knife - greater pressure can be applied with the same force as it has a smaller contact area
3.4. can be reduced by increasing the contact area
3.4.1. eg. farm tractors have large and wide tyres that reduce the pressure applied on the soft soil.
4. Types of forces
4.1. Gravitational force
4.1.1. The Earth exerts a pulling force on all objects
4.2. Frictional force
4.2.1. The force that acts to oppose the direction of motion
4.3. Magnetic force
4.3.1. The force acting on magnetic materials
5. Effects of force
5.1. make a stationary object move
5.2. increase or decrease the speed of an object
5.3. change the direction of a moving object
5.4. change the shape and size of an object
6. Gravitational force
6.1. The force that causes all objects to fall to the ground.
6.1.1. Without gravity, objects would be floating in the air
7. Magnetic force
7.1. Are exerted by magnets
7.2. All magnets have two poles - North Pole (N) and South Pole (S)
7.3. Like poles repel while unlike poles attract
7.4. Magnets exert a pulling force on magnetic materials like iron, steel, cobalt and nickel.
7.5. Can act at a distance
8. Frictional force
8.1. Is produced when two surfaces in contact with each other rub against one another.
8.2. Slows down and/or stops the motion of an object
8.3. acts in the opposite direction to motion.
8.3.1. prevents stationary object from starting to move when forces act on them
8.3.2. can also slow things down
8.4. Without friction, we are unable to walk and vehicles cannot be operated
8.5. can also be a nuisance
8.5.1. can overheat machines
8.5.2. causes wear and tear
8.5.2.1. eg. car tyres and the soles of our shoes
8.6. can reduce unwanted friction
8.6.1. lubricating
8.6.2. polishing the surface; smooth surface
8.6.3. using ball bearings