1. cutting makes use of pressure. a sharp knife has smaller contact surface with an object as force acts on a small area so the pressure is high.
1.1. with a blunt knife, the same force acts over a large area. this lowers the pressure. thus easier to cut things with a sharp knife
2. a force is a push or a pull
2.1. A push or a pull.
3. What are the effects of forces?
3.1. change the speed of a moving object, either by increasing or decreasing its speed
3.2. change the shape or size of an object
3.2.1. New node
3.2.1.1. New node
3.3. start an object moving
3.4. stop a moving object
3.5. change the direction of an moving object
4. We cannot see a force but we can see the effects.
5. how to measure force?
5.1. force-meters[;
5.1.1. spring balances
5.1.1.1. extension
5.1.1.1.1. spring stretches when a force pulls on it
5.1.1.1.2. greater the force, the more the spring stretches
5.1.1.2. compression
5.1.1.2.1. spring is compressed when a force acts on it
6. SI unit for force
6.1. Newton (N)
7. important forces(:
7.1. frictional force
7.1.1. Friction or frictional force occurs when 2 moving surface are in contact
7.1.2. friction slows down and stops a moving object
7.1.3. friction produces heat
7.1.4. friction is also useful
7.1.4.1. hols a nail in the wall
7.1.4.2. friction between the brakes and wheels of the bicycle slows down the bicycle
7.1.5. friction can be a problem D:
7.1.5.1. makes movement more difficult
7.1.5.2. wears off the materials
7.1.6. ways to reduce friction
7.1.6.1. lubricant
7.1.6.2. ball bearings
7.1.6.3. streamlining
7.2. magnetic force
7.2.1. a magnet can attract objects made up of iron or steel. the magnet exerts a force called magnetic force.
7.2.2. e.g. compasses, fridge,crane that lifts iron and steel objects
7.2.3. a magnet can exert a force on other magnets.
7.2.4. a magnet has 2 poles, north and south.
7.2.5. like poles of a magnet repel each other while unlike poles of a magnet attract
7.3. gravitational force
7.3.1. is a force that pulls objects towards the earth
7.3.2. gravity exerts between any 2 objects
7.3.3. weight
7.3.3.1. weight of and object depends on the force of gravity pulling on that object
7.3.3.2. greater the force puling that object, the heavier the object. for example, you weigh more on earth than on mars. this is because force of gravity is greater on earth than on mars.
7.3.3.3. weight is a force
7.3.3.4. measured using a spring balance
7.3.3.5. measured in newtons
8. pressure
8.1. sometimes, a large amount of force is not able to push or pull a small object
8.2. is dependent on force and area
8.3. pressure increases when force increases or the area decrease
8.4. increasing pressure by reducing area
8.4.1. for the same force, when a smaller surface area is in contact with an object, the pressure exerted on the object will be higher.