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How to teach force & pressure and it's misconceptions
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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
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