FORCES

A push

A pull

A twist

A FORCE IS

Using a spring balance

The unit forces are measured in is the newton (after Sir Isaac Newton)

The symbol for a newton is N

Forces can be measured

We draw forces using an arrow The arrow shows the direction the force is

acting in The size of the arrow shows how big or

small the force is This shows a large force

This shows a small force

HOW to draw a Force

A. The SPEED of an object It can make something move It can speed something up It can slow something down It can make something stop moving

eg. hand twisting a door knobeg. wind pushing on a saileg. girl pushing a rockeg. a stone being pulled towards the earth by the

force of gravity

A force can cause a CHANGE in

B The SHAPE of an object

eg. a crashed careg. a squashed pillow

Also

C The ENERGY of an object

Eg. the stones gravitational potential energy changes to kinetic energy when the force of gravity acts on it

and

This means that the force acts between objects that can TOUCH each other

eg. a girl pushing a rockeg. the force of friction which acts when one

surface is moving across other surfaceeg. wind pushing a windmill bladeeg. a girl pulling on a fishing rodEg. a bat hitting a ball

A force can be a CONTACT FORCE

This means that the force acts between objects that DO NOT TOUCH each other

eg. magnetic forceeg. gravitational forceeg. electrostatic force

A Force can be a NON CONTACT FORCE

1. If the forces on an object are BALANCED (even on all sides), the object will

KEEP DOING WHAT IT IS ALREADY DOING

This means it will keep stationary (still) ORkeep moving at a STEADY (CONSTANT) SPEED

ie. the motion will not CHANGE

Newton said

2. If the forces on an object are UNBALANCED (not even on all sides) the object willCHANGE WHAT IT IS DOING

This means it will Start moving if it was stationary

ORIf it was already moving the object will Move fasterSlow downTurn a cornerie. the motion will CHANGE

He also said that

1. Describe the MOTION (or lack of motion) of the object to decide whether the forces are balanced or not

2. Decide what forces are acting on the object3. Draw the force arrows around the object, begin

arrow at the centre of the picture and label them4. Make sure the arrow head is facing away from the

picture5. Draw large arrows for large forces and small

arrows for small forces6. Draw the force of gravity pulling downwards on all

objects on or above the earths surface

DRAWING FREEBODY DIAGRAMS

Make things change their SHAPEEg. crushing a can in a can crusher. The

unbalanced force is downwards

Make things change their DIRECTIONEg. a bus turning a corner. The unbalanced

force is towards the inside of the turn

Unbalanced Forces

When 2 different massesare dropped from the same height they;

Travel downwards at the same speed Have the same acceleration (they speed

up the same amount) Are pulled downwards equally because the

force of gravity on each mass is the SAME

Falling objects

The masses hit the ground at the same time.

(remember coin/feather and Galileo’s cannon balls)

This means that…..