ForcesYear 11 Physics

Learning Intentions• To identify the effect of forces acting

on an object

• To recall some common examples of forces

Book Reference• Page 33 Physics for CCEA

A force is a push, pull or twist.

What you should already know…

Say if the following are pushes, pulls or twists:

Writing on paper

Typing on a keyboard

Tug-of-war

Unscrewing the top off a bottle

Posting a letter through a door

Putting on a pair of socks

Turning a door handle

Pull

Pull

Push

Push

Push

Twist Twist

Twist Twist

Demos• What is the effect of the force on the

object?

• Can you name the force causing the effect?

Rocket Launcher• Start object moving

• Thrust

The Parachute Opening• Decreasing in Speed

• Air Resistance

Airplane Take-off• Changing Direction

• Lift

F1 Car• Change Shape

• Reaction Force

The effects of a forceA force can cause an object to…

• Increase/decrease in speed

• Change direction

• Change shape

• Start moving or stop moving

Learning Intentions- Identify and label forces acting on an

object

- Recall some common examples of forces

- Use a Newton balance to measure forces

Name a force

Describing the forces

1. Magnetism

2. Friction

3. Compression

4. Tension

a. When 2 material rub together

b. When a material is being stretched

c. When a material is being squashed

d. Enables compasses to work

5. Gravity

6. Nuclear

7. Air resistance

8. Electrostatic

e. Holds the particles in a nucleus together

f. When an object moves through air

g. The force that exists between all objects with mass

h. The force you get between two charged objects

Some Force definitions

When an object is moving it comes in contact with small

particles in the air. The collisions cause an opposition to the

movement.

An engine or motor uses this force to cause an object to

move.

This force is experienced when an object is in water, it is

sometimes called buoyancy.

The force associated with a string or a rope

being stretched.

The Force which opposes the motion of

an object, it is also needed to give your

shoes grip on the ground

When an object’s weight is larger than this force then the object will break

through- it is a contact force and acts in the opposite direction to

weight.

FRICTIONTENSIONUPTHRUST

THRUSTAIR RESISTANCEREACTION FORCE

Learning Intentions- Identify and label forces acting on an

object

- Recall some common examples of forces

- Use a Newton balance to measure forces

Force diagramsForce diagrams help us understand forces.

The force is represented by an arrow.

The direction the arrow points shows the direction the force is acting.

The size of the arrow can be used to compare the size of the forces.

A force diagram for a falling object just after it starts to fall.

Air resistance

Weight

Unused homework diary on a table

What force pulls down on the book?

Gravity

The diary does not move, so there must be an equal and opposite force pushing up on the diary.

What do we call this force?

Reaction force

Gravity

Reaction force

Forces on a speeding fish

Upthrust

FrictionThrust

Weight

What is thrust?

A forward push

What is upthrust?

The upwards force on a body in a liquid or a gas

Label the forces acting on the moving ship shown:

Upthrust or buoyancy

Thrust

Air resistance

Friction

Weight

Use the Force• In each of the examples draw the object

with all the forces acting on it (name and direction)

1. A man standing on a bridge (2)

2. An aeroplane flying high in the sky (4)

3. A ball falling vertically through the air (2)

4. A fishing line (2)

Measuring Forces• A force metre (also called a Newton

balance) can be used to measure the size of a force. The standard unit used for force is the newton (N)

The force that you… Size of Force (N) Name of Force

need to double the length of a spring

apply to the ground

work against to drag your bag along the desk