Force & Pressure

1. What is a force?

1.1. A force is a push or pull

1.2. A force is exerted when one thing interacts with another.

1.3. Forces are all around us, everything we do needs a force.

2. What are the effects of force

2.1. Change the speed of a moving object

2.2. Change the shape or size of an object (eg. Plasticine)

3. How can we measure force?

3.1. Forces are measured with force-meters. Examples of force-meters are spring balances.

3.2. The two types of spring balances are extension spring balances and compression spring balance.

3.3. In a extension spring balance, it measures the force the objected exerts when the spring stretches.

3.4. In a compression spring balance, the spring would compress when a force acts on it

4. Types of forces

4.1. Frictional force

4.1.1. Advantages

4.1.1.1. The friction between the brakes and the wheels helps to slow down the bicycle.

4.1.1.2. The friction between our hands and an object helps us to hold it.

4.1.1.3. The friction between two stones can create a fire.

4.1.2. Disadvantages

4.1.2.1. But sometimes friction can be a nuisance.

4.1.2.2. The friction between the tyres of the vehicle and the road wears out the tyres. Thus, the vehicles may skid on rainy days and cause an accident.

4.1.2.3. The friction between the air and the cyclist slows down the speed of the cyclist.

4.1.3. Friction is a force which slows down and stops a moving object.

4.1.4. It occurs whenever two moving surfaces are in contact.

4.1.5. In addition, it also produces heat.

4.1.6. But friction has advantages and disadvantages also.

4.2. Magnetic force

4.2.1. Magnets exert a magnetic force can attract objects made of iron and steel.

4.2.2. Magnets are being used almost everywhere in daily life.

4.2.3. You can see them in the needle of a compass, the door of the fridge and many more things.

4.2.4. When like poles face each face other, they repel. When unlike poles face each other, they attract.

4.3. Gravitational force

4.3.1. Gravitational force is a force which pulls the objects toward the Earth. It is also known as gravity. The weight of an object depends on the force of gravity pulling on that object. The greater the force of gravity pulling an object, the heavier the object.

5. What is pressure?

5.1. Although force is a push or a pull, sometimes a large amount of force is needed to push or to pull a small object. (e.g. A thumbtack)

5.2. You may be able to push the thumbtack into a wooden board but you cannot push your whole thumb into the wood.This is due to area as the point of the thumbtack has a small area and the force act on a small area to give a high pressure. Thus the area of your thumb is greater than the area of the thumbtack and is thus spread over a larger area, thus the pressure is lower.

6. Increasing pressure by reducing area

6.1. pressure depends on two things: the area and the force.

6.2. When more force is exerted, the higher the pressure. The smaller the area, the higher the pressure.

6.3. When there is less force exerted, the lower the pressure and the larger the area, the lower the pressure as well.

7. Lowering pressure by increasing the contact area

7.1. The large surface area of the skis prevent the skier from sinking into snow.

7.2. Farm tractors have a wide tires that reduce the pressure applied on the soft soil by the tractor.

7.3. When the surface area is greater,it lowers the amount of pressure.

8. Calculating pressure

8.1. The SI Unit of pressure is Pascal.

8.2. Pressure= Force/Area