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What is a force?

A force is a push, pull or twist.

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

Push

Push

Pull

Twist

Twist

Push

Pull

Twist

Twist

Types of force you need to know……

Gravity

Friction

Air resistance

Magnetism

Tension

Electrostatic

Nuclear

Compression

Describing the forces

The force you get when two material rub together

The force you get when a material is being stretched

The force you get when a material is being squashed

The force that enables compasses to work

Magnetism

Friction

Compression

Tension

Describing the forces

Gravity

Nuclear

Air resistance

Electrostatic

The force that holds the particles in a nucleus together

The force you get when an object moves through air

The force that exists between all objects with mass

The force you get between two charged objects

Attractive or repulsive?

Gravity?

Magnetism?

Electrostatic?

Attractive, always

Attractive and repulsive

Attractive and repulsive

Contact and non-contact

If two objects or materials need to be touching for the force to have an effect then it is a C________ force.

Examples:

If two objects or materials do not need to be t______ for the force to have an effect then it is a NON CONTACT force.

Examples:

ONTACT

Friction

Airresistance

ouching

Gravity

Electrostatic

Magnetic

Gravity

Gravity is an attractive f____ that exists between all m_____. Gravity is always a_______.

The l____ the mass is, the greater the gravitational attraction. The f_____ away a mass is, the less the gravitational attraction.

Your w____ is the pull of the Earth’s gravity on your body.

If you stood on the M___ you would weigh less than on Earth.

This is because the Moon has less mass than Earth, so the Moon’s g_________ pull is weaker than the Earth’s.

orce

asses

ttractive

arger

urther

eight

The Moon is kept in orbit around the Earth due to gravity.

oon

ravitational

10kg

Weight = 100 N

Mass and weightWhat is the difference between mass and weight?

Your mass is a measure of how many particles there are in your body. It does not matter where you are in the Universe, your mass does not change.

Your weight is a measure of the pull of gravity on your body. Your weight depends upon what planet you are standing on.

You would weigh less on Mercury than on Earth because Mercury is smaller than Earth.

What is mass measured in?

Kilograms

What is weight measured in?

Newtons

Draw a force diagram for a falling object when it first starts to fall.

Air resistance

Weight

Force diagramsForce diagrams show you the direction a force is acting in. It shows you the direction an object is being pushed, pulled or twisted. The direction of the arrow shows you the direction of the force. The sizes of the arrows can be used to compare the sizes of the forces.

Unused homework diary on a table starts to fall.

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

Forces on a speeding fish? starts to fall.

What is thrust?

A forward push

What is upthrust?

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

Upthrust

Friction

Thrust

Weight

Label the forces acting on the moving ship shown: starts to fall.

Upthrust or buoyancy

Air resistance

Thrust

Friction

Weight

A ship arrives at port and is loaded with cargo: starts to fall.

What happens to the weight of the ship?

What happens to the upthrust on the ship?

Which is the largest force, weight or upthrust?

Increases

Increases

Both equal

Forces and motion starts to fall.

If an object is stationary and an unbalanced force acts on it, it will start to move.

If an object is moving and an unbalanced force acts on it there are three possibilities…

The object could speed up.

The object could slow down.

The object could change direction.

In which direction, if any will the following stationery objects move?

What is friction? objects move?

If you rub your hands together there is resistance to the motion.

What do we call this force?

Friction

What causes it?

Even though your hands look smooth, on a microscopic level it is not, so when your hands rub together you get the resistive force of friction.

Direction of friction objects move?

Friction always acts in the opposite direction to the way an object is moving.

For the following moving objects, mark with an arrow, the direction friction is acting in.

Friction effects objects move?

Friction always acts in the o______ direction to which an object is moving in.

Friction is a type of f____.

Whenever you get friction between two objects you always get h___ and w_____.

You can reduce the effect of friction by using a l______. O_ is a lubricant used in car engines to reduce friction effects.

pposite

orce

eat

earing

ubricant

il

Starting moving… objects move?

An object will only start to move if the forces applied to it overcome any frictional forces. For the examples shown say if the stationary objects will move or not, and if they do move, say in which direction.

Friction - useful or hindrance? objects move?

Write down three instances where friction is useful and three where it is a hindrance.

Discuss your ideas with the class and then have a vote on what the class thinks are the top three for each.

For a fish in water, what do we call force Z? objects move?

- Friction
- Air resistance
- Gravity
- Upthrust

Z

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