GCSE Science | Forces

Resultant Force

  • the overall force acting on an object
  • (sum of all forces combined)

Newton's Second Law

  • F = m x a
  • W = m x g

Newton's First Law

  • if there is a resultant force, an object will accelerate or decelerate
  • if there is no resultant force, an object will
    • remain stationary, or
    • continue at a constant speed

(if you know the names of the force, replace them e.g. weight/ air resistance/ friction/ driving force/ drag)

Skydiver reaching terminal velocity

  • first, their downward force is bigger than their upward force.
  • this causes them to accelerate downwards.
  • then, the upward force increases (they are hitting the wind faster)
  • eventually, downward force = upward force.
  • this causes them to fall at a constant speed.

Car reaching terminal velocity

  • first, forward force is bigger than the backwards force.
  • this causes the car to accelerate forwards.
  • then, the backwards force increases
  • eventually, forward force = backwards force
  • this causes the car to continue at a constant speed.

Newton's Third Law

  • when two stationary objects interact,
  • they exert an equal and opposite force on each other.
    • my laptop has a weight (downward force)
    • this means the table must have a reaction force (upward force)

Springs

  • F = ke
    • Force (N)
    • extension (m)
    • spring constant (N/m)
  • Hooke's Law - the extension of a spring is directly proportional to the force applied - until the limit of proportionality
  • Elastic - will return to original shape
  • Plastic - will not return to original shape
  • Elastic potential energy - energy transferred to a stretched object