KS4 Forces - Forces







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What is a force?


Say if the following are pushes, pulls or twists:

Writing on paper

Typing on a keyboard


Unscrewing the top off a bottle

Posting a letter through a door

Putting on a pair of socks


Types of force you need to know……

Friction Gravity

Magnetism Air resistance





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


Describing the forces



Air resistance


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


Attractive or repulsive?




Attractive, always

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.


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



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 oon ravitational


Mass and weight

What 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.

What is mass measured in?


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 weight measured in?


10kg Mass = 10kg


Force diagrams

Force 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.

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

Air resistance


Unused homework diary on a table

What force pulls down on the book?


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


Forces on a speeding fish?


Friction Thrust


What is thrust?

A forward push

What is upthrust?


Label the forces acting on the moving ship shown:

Upthrust or buoyancy


Air resistance



A ship arrives at port and is loaded with cargo:

What happens to the weight of the ship? What happens to the upthrust on the ship?

Which is the largest force, weight or upthrust?


Forces and motion

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.


What is friction?

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

What do we call this force?

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


Direction of friction

Friction always acts in the opposite direction to the way

an object is moving.

For the following moving objects, mark with an


Friction effects

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.



eat earing


Starting moving…

An object will only start to move if the forces applied to it


Friction - useful or hindrance?



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


Which of the following is not a force?

A. Heat

B. Gravity

C. Tension

D. Friction


For a man standing up, in which direction

does gravity act?






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

A. Friction

B. Air resistance

C. Gravity

D. Upthrust


In what units is force measured in?

A. Joules

B. Metres

C. Newtons

D. Seconds


What device is used to measure force?

A. Clock

B. Voltmeter

C. Joulemeter