Resultant Forces | Physics for GCSE/IGCSE - Year 11 PDF Download

Forces - Basics

• A force is defined as: A push or a pull that acts on an object due to the interaction with another object
• Forces can affect bodies in various ways:
  • Changes in Speed: Forces have the ability to either increase the speed of an object (speed up) or decrease it (slow down).
  • Changes in Direction: Forces can alter the direction in which an object is moving, causing it to change its path or route.
  • Changes in Shape: Forces can lead to the stretching, compressing, or deformation of objects.

Resultant Forces on a Straight Line

• A resultant force is a singular force that encompasses all forces acting on an object.
• When multiple forces act on an object, they can be added together to form a single resultant force, summarizing their combined effect.
• This resultant force dictates:
  • The direction in which the object will move due to the collective impact of all forces.
  • The magnitude of the final force experienced by the object.
• The resultant force is also referred to as the net force.
• Forces can lead to two outcomes:
  • Balanced forces: Forces combine in a manner that nullifies each other, resulting in no net force acting on the object.
    • For instance, the weight of a book on a desk is counteracted by the desk's normal force, resulting in equilibrium.
  • Unbalanced forces: Forces combine unevenly, resulting in a net force that imparts motion to the object.

Unbalanced forces occur when forces combine in a manner where they don't completely cancel out, resulting in a resultant force acting on the object.

• For instance, envision two individuals engaged in a tug-of-war, each pulling against the other from opposite ends of the rope. If person A exerts an 80 N force to the left while person B applies a 100 N force to the right, these forces won't cancel each other out entirely. As person B exerts greater force than person A, the forces become unbalanced, leading to a resultant force of 20 N to the right acting on the rope.

Practical Examples

Imagine forces as two people pushing on boxes:

• In the first scenario, if both people are evenly matched, the box remains stationary.
• In the second scenario, if the people push on the same side, the box moves to the right.
• In the third scenario, if the people push against each other unevenly, a resultant force is observed to the left.