1.2. Negative effect about friction: Wears away material , make movement difficult and produce heat.

1.3. How to reduce friction: Using ball bearings, lubricant, using a smooth surface and streamlining

2. 1 worked example

2.1. An hippopotamus weighs 20 000N. It stands on one foot with an area of 1 000cm2. What is the pressure on the ground?

2.2. Pressure = Force / Area = 20 000N / 1000cm2 = 40 N/cm2

3. How to calculate pressure?

3.1. Pressure = Force / Area

3.2. The unit of force is the newton (N)

3.3. New node

4. Exam Question

4.1. A rectangular glass tank used in zoos and meant for the polar bears to swim in has a horizontal cross-section of 10 m 5 m and a vertical height of 6 m. Water of weight 2 000 000 N is filled to a depth of 4 m. Calculate the pressure on the base of the tank due to the weight of the water.

4.2. Pressure = 2 000 000N / (10 m x 5 m) = 40 000 Pa

5. What is force?

5.1. A push or a pull

6. How to measure force?

6.1. Use force meters / newton meter

6.2. Example: Spring balance

6.3. SI unit for friction: Newton

7. Type of forces

7.1. Frictional force, gravitational force, magnetic force and elastic spring balance

8. Gravitational force

8.1. Gravity exist between in any two objects.

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

9. Magnetic force

9.1. Force exerted by a magnet on a magnetic material.