Difference Between Force and power

What is a Force?

  • A force is a push or pull
  • Acts on an object
  • Requires an agent
  • Is a vector
  • Is a contact force or a long range force

Newton’s First Law: Consider an object with no force acting on it. If it is at rest, It will remain at rest; if it is moving, it will continue to move in a straight line at a constant speed.

What is Power?

Power is the way we measure how quickly energy is being changed. When we look at the power of a moving object, we are really looking at how fast work is happening.

Example:

A lift motor has to move a fully laden lift 4m between floors in 1.5s.

The lift has a mass of 1850 kg (ignore friction).

a) Calculate the weight of the fully laden lift.

W = mg = 1850 x 10 = 18500N

b) What is the upward force in the cable when the lift is moving at a constant speed?

At constant speed, forces must be balanced. Upward force = downward force (weight) Upward force = 18500 N

c) What is the work done by the motor?

WD = F x d = 18500 x 4 so WD = 74000 J

d) What is the minimum power of the motor to raise the lift at a steady speed?

Steady speed means forces are balanced. ! Power = work done time = 7400 1.5

So Power = 49333 W

Difference between force and power:

Classification Power Force
Unit watt = joules/second

newton
Definition Power is the rate at which work is done, or energy is transmitted. A push or a pull resulting from an interaction between objects.
Symbol P F
Derivations from other quantities P = w/t (power = work divided by time) F = m a (force = mass multiplied by acceleration)
Everyday Example Horsepower (1 horsepower = 750 Watts). Gravity, friction, magnetism.
Relation to “Work” Rate at which work is performed. Force applied over a distance creates work.
Named After James Watt Isaac Newton

Practise This Question

Two lenses with powers; 2D & -4D are kept together. What is the effective focal length of the combination?