FORCE AND PRESSURE

RELATIONSHIP BETWEEN FORCEAND PRESSURE

FRICTION

EFFECTS OF FORCE

INTRODUCTION

FORCE

- playing a guitar - scrubbing the floor - sawing wood - rowing a boat

• A pull is when we apply a force to move an object towards our body

• A force to move an object away from our bodies

FORCE

A force is a push or a pull or both. A force cannot be seen but we can feel andobserve the effects of the force.

PUSH PULL

COMBINATION OF PUSH AND PULL

Stops a moving object or makes astationary object

moves

Change thespeed of a

moving object

Change thedirection of amoving object

Changes theshape

permanently

Changes theshape

temporarily

EFFECTS OFA FORCE

Stretch a rubber bandStretch a rubber band

After

An object that will return to its original shape and size after being squeezed, pressed, twisted and stretched is elastic

After After

Press a spongePress a sponge Squeeze a springSqueeze a spring

Drop a glassDrop a glass

After After

Tear a piece of paperTear a piece of paper

After

Crush an empty canCrush an empty can

An object that will not return to its original shape and size after being squeezed,pressed, twisted and stretched is inelastic

MISCONCEPTION???

A solid cannot be compressed or stretched!!

CHILDREN’S MISCONCEPTIONCHILDREN’S MISCONCEPTION

EXPLANATIONEXPLANATION

The shape of a solid object changes when a force is applied to it whether it’s temporarily or permanentlyExample: crushing a can – changes the shape permanently

when a force is applied in the opposite direction (or different direction), the moving object will change its moving direction

MISCONCEPTION???

Misconception?A force is needed to keep an object moving with a constant speed

Explanation:You do not need forces to move at a steady speed but if you keep the same speed yet change direction, like a moon around a planet, then you have a force acting on you anyway

An object will move faster when a force is appliedIt moves in the same direction as the applied force

• A stationary ball will move when it is kicked • Moves in the same direction as the applied force

•The moving ball will stop when an equal force is applied in the opposite direction of its motion

MISCONCEPTION???

Force is a property of an object. An object has force and when it runs out of force it stops moving

EXPLANATIONEXPLANATION

an object at rest or in motion will remain in that state unless an external force is applied to the object

Newton 1st Law

FRICTION- Occurs when two

surfaces are moving in contact with each

other

Factors that effectfriction

Physical condition of the surface

Weight ofan object

Advantages• enables people to run and walk without falling or slipping• enables us to write on paper• enables a car to stop when the brakes are applied• enables an object to be stationary • music instruments can produce sound• allows vehicles to travel on the road without slipping

Disadvantages• slows down a moving object• causes the surfaces of objects to wear out• causes less effectiveness of moving machine• causes heating• causes sound pollution • increases cost when worn-out objects need to be replaced with new ones

Ways to reduce• use ball bearing• use wheel and axle• use lubricants such as grease or oil• use air cushion• use roller bearing

MISCONCEPTION???

Friction is only present when something is rubbing against a moving object

EXPLANATIONEXPLANATION

Occurs when two surfaces are moving in contactwith each other

Examples of friction

RELATIONSHIP BETWEEN FORCE AND PRESSURE

• AIR PRESSURE

BICYCLE PUMPA force is applied to the pump toproduce air pressure

Applyingforce

Pull and push