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Study notes

Forces

Forces are pushes or pulls that can change the speed, direction, or shape of objects through contact or non-contact action.

Learn it step by step

What is a Force

A force is simply a push or a pull exerted on an object. We cannot see a force itself, but we can always observe its effects on objects around us.

Effects of Forces

A force can make a stationary object start moving, make a moving object stop or change speed, change the direction of a moving object, or change the shape of an object.

Contact Forces

Contact forces only occur when two objects are physically touching each other. Examples include frictional force, elastic spring force, and applied push or pull forces.

Non-Contact Forces

Non-contact forces can act over a distance without physical contact between the objects. Examples include gravitational force, magnetic force, and electrostatic force.

Friction and Gravity

Friction is a contact force that opposes motion between two surfaces in contact. Gravity is a non-contact pull that attracts objects towards the center of the Earth.

Worked examples

A boy kicks a stationary football on the field. State two effects of the force applied by his foot on the football.
  1. Identify the initial state of the football, which is stationary.
  2. Recognize that the kick applies a push force to the football.
  3. State the first effect: the force makes the stationary football start to move.
  4. State the second effect: the force changes the shape of the football temporarily upon impact.
Why is it harder to push a heavy box across a rough wooden floor than a smooth tiled floor?
  1. Identify the force acting against the motion, which is friction.
  2. Compare the two surfaces, noting that a rough wooden floor has more irregularities than a smooth tiled floor.
  3. Conclude that a rough floor creates greater frictional force, requiring more push force to overcome it.
A metal ball is dropped from a balcony and falls to the ground. Name the force acting on the ball as it falls and state its direction.
  1. Identify the force pulling the ball down without physical contact, which is gravitational force.
  2. Determine the direction in which gravity acts on Earth.
  3. State that the gravitational force pulls the metal ball downwards towards the center of the Earth.

Mind map

Mind map for forces.

  • effects
    • start or stop motion
    • change speed or direction
    • change shape
  • contact forces
    • friction
    • elastic spring force
    • applied push or pull
  • non-contact forces
    • gravitational force
    • magnetic force
  • friction
    • opposes motion
    • depends on surface roughness
  • gravity
    • pulls objects to earth
    • acts without contact
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