Forces Are Due To An Interaction

key notes:

Definition of Force:

  • A force is a push or a pull that can change the motion of an object. Forces are measured in newtons (N).

Interaction-Based Forces:

  • Forces are the result of an interaction between two objects. When objects interact, forces act between them.
  • There are two types of interactions:
    • Contact forces: Forces that occur when objects are physically touching (e.g., friction, tension).
    • Non-contact forces: Forces that act at a distance without physical contact (e.g., gravitational force, magnetic force, electrostatic force).

Types of Forces:

  • Gravitational Force: A force of attraction between any two objects due to their mass.
  • Electromagnetic Force: This includes electric forces (between charged particles) and magnetic forces (between magnetic poles).
  • Contact Forces:
    • Friction: The resistance to motion when two surfaces are in contact.
    • Tension: The force transmitted through a string, rope, or wire when it is pulled tight.
    • Normal Force: The support force exerted by a surface perpendicular to the object resting on it.

Action and Reaction Forces (Newton’s Third Law):

  • Newton’s Third Law of Motion states that for every action force, there is an equal and opposite reaction force.
  • These forces always come in pairs: when one object exerts a force on another, the second object exerts an equal but opposite force on the first.

Force and Motion:

  • The force applied to an object can affect its motion. It can cause an object to start moving, stop, or change its direction.
  • Balanced Forces: When forces acting on an object are equal and opposite, they cancel each other out, and the object does not move.
  • Unbalanced Forces: When forces are unequal, they cause a change in the object’s motion (acceleration).

Examples of Force Interactions:

  • A person pushing a box (contact force).
  • Earth pulling an apple downward due to gravity (non-contact force).
  • Two magnets attracting or repelling each other (electromagnetic interaction).

Units of Force:

  • The unit of force is the newton (N), named after Sir Isaac Newton.
  • One newton is the force required to accelerate a one-kilogram mass by one meter per second squared.

Let’s practice!