Forces and Motion

Everything in the world is being influenced by forces

Force is just a fancy word for something that pushes or pulls.

If we push a chair, we are applying a force to it. If I pick up a coffee cup, I am apply a force to it. If I jump I am applying force.

Applying force can change the direction that objects are moving in, and their shape.

We can’t actually see a force, but what you can see is the effect of them on the object.

If I drop a tennis ball, I can see the ball falling quickly to the ground due to gravity.

When a ball is resting on a table high up, the table is pushing up with a force equal to gravity pushing down.

As you probably know there are different types of forces.

Contact and non-contact forces exist in our world.

When forces act, due to touching they are called a contact force (Friction, tension force, spring force, applied force and normal force).

Non-contact force don’t need to touch the object to have an effect on them (gravity and magnetic forces).

All forces act in pairs, these pairs are called interaction pairs.

If we look at the image to the left, we see a women hanging off a tree.

The tree supports the women's weight and at the same time the women pulls on the tree.

Even as a tennis ball falls, air resistance is pushing up against it, countering gravity.

As we said before, we can’t actually see these forces, but we can see the affect they have on an object.

Therefore we can also measure the force on an object.

We can measure forces using a newtonmeter. All forces are measure in Newtons (N).

100 grams is equal to 1 newton. This means if you hold a 5kg (5000g) dumbbell in your hand, your lifting 50 newtons.

Short Answer Questions

1. What is a force?

2. What is the difference between a contact and non-contact force

3. As a ball falls through the air, explain the forces which act on it

4. Why do sky divers use a parachute? Explain your answer (4 marks)

5. Copy and complete this sentence:

A force is a ______ or a ______. We can show the forces acting on an object using force ________. Forces come in pairs called ________ pairs. To measure forces you use a ________.

6. Explain why it is better to have a plan with a pointed nose rather than a blunt nose?

7. What is meant by the term ‘balanced forces’?

Questions

When these two forces acting on an object are equal, but act in opposite directions, they are said to be balanced forces.

If the forces on an object are balanced then then a stationary object will stay still and a moving object will continue to move in the same direction and speed.