Physics-forces

Introducing forces

What is a force?

You cannot see a force but you can see its effects. It can change the shape, speed and/or the direction of an object. In some situations, forces present but you cannot see any effects.

Pushes and pull:

  • A force can either be a push or a pull acting on an object.

  • Hitting a ball is an example of push force.

  • Towing a car is am example of push force

Measuring forces:

  • A force has both size and direction. Forces are drawn as arrows.

  • The head of an arrow shows the direction of the force and the length shows the size of the force.

  • The size of a force is measured in units called newtons

  • Forces are measured using a force meter.

Balanced and unbalanced forces:

If two forces act in the same direction on an object then the net force can be found by adding the two forces together. If two forces act in opposite directions on an object the net force can be found by subtracting the two forces.

If two forces are equal in size and act in opposite directions on an object, the net force is zero, making it unbalanced.

Newtons laws of force and motion

  1. The first law states that if the forces acting on an object are balanced, then the object will remain stationary or carry same speed in the same direction.

  2. The second law states that if unbalanced forces acting on an object, the object will accelerate in the direction that the net force acts.

  3. The third law states that when a force acts on an object, an equal and opposite reaction force occurs. This is called ‘action-reaction’.

Types of forces

  • air resistance - a type of frictional force that acts on an object as they move through the air

  • Gravity - an attractive force between objects because of their mass

  • Electrostatic - force between objects that have an electric charge

  • Tension - a force transmitted through a rope, string, cable or chain when it is pulled tight by forces acting on opposite ends

  • Compression - a pushing force that squishes or squeezes an object.

  • Friction - a force that resists motion when two surfaces rub each other.

  • Thrust - a force that pushes an object forwards

  • Buoyancy - upward force that a fluid applies to an object that is immersed in it, it makes the object float.

  • Magnetic - the force that magnets exert on certain materials (iron, nickel etc) either attracts (pull) or repel (push)

  • Support - the force that a surface applies upward to support an object.