Force and movement

A force is a push or a pull.

 Watch this video to learn about force and movement

 

A force is a push or a pull of an object.

If a push or a pull is applied to a book on your desk, we say force has acted on the book whether the book changed its position or not.

 The harder you push or pull an object the greater the force you use.

This means we apply more force on heavier objects than on lighter ones.

Gravity is an example of a force because it pulls objects downwards towards the earth.

Similarly friction is a force because it acts in the opposite direction that force is applied.

Friction opposes motion.

Units of force

Force is measured in Newtons.

The symbol for Newtons is N.

Force can be measured using a spring balance.

1 Kg is equal to 10N

Friction

Friction is a force that opposes motion.

Friction acts between two surfaces that are in contact or that move over each other. e.g. the book on the table.

When you rub your hands together you feel some resistance that is caused by friction.

If you continue rubbing your hands rapidly then you will feel some heat or warmth in your hands.

This is an effect of the force of friction.

Friction has both advantages and disadvantages in our daily lives.

 

Advantages of friction

  • Friction makes a pen write.

  • Friction helps us in walking.

  • Friction helps in stopping moving objects for example cars.

  • Friction helps in lighting a match.

Disadvantages of friction

  • It wears down moving parts of a machine

  • It produces heat, which may be harmful and not required in a process.
  • It wears out shoes.

There is more friction between the shoes and the grass than the snow and the snowblades.

The wheel in contact with road exhibits rolling friction.

Increasing friction

Force of friction can be increased by:

  • Increasing the force between the two surfaces that are in contact by increasing the weight of the objects.

  • Increasing the roughness of the two surfaces that are in contact. e.g. in sand paper,files

 

Friction can be reduced by

  • Oiling or greasing (lubricating) the moving parts or the surfaces that are in contact.

Oil or grease is applied to the hinges of doors and windows to reduce friction.

Engines and machines are lubricated with oil to reduce friction.

  • Using rollers between the moving parts.

  • Using ball bearings between the moving parts.

  • Reducing force between the moving parts.
  • Making the two surfaces in contact be as smooth as possible.
  • By separating the contact surfaces by an air cushion e.g., a hovercraft, can travel over rough land, swamp or sea.

Try this short quiz



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