What is a Force?
Force is defined as the interaction between two bodies or it can also be defined as the push or pull experienced by an object when an external force acts on it. The other way of explaining force is it is a responsible factor for an object to be either in the state of motion or state of rest until an external force acts on it. Force is expressed in terms of Newton.
This is the concept that is explained in Newton’s first law of motion.
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 its motion in a straight line at a constant speed.
Force can either through contact or non-contact force.
Examples of contact forces are pushing a box and kicking a ball while examples of non-contact force are gravitational force and electrostatic force.
Force = (Mass)(Acceleration)
What is Power?
Power is defined as the amount of energy consumed when work is done in unit time. Power can also be defined as the rate at which work is done.
Power = Work done/Time taken
Watt is the unit of power.
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:
|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.|
|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|
Relation between Force and Power
Also, power and force are related to each other.
We know that power is work done per unit time and it is expressed as:
P = W/ΔT
Work can be said as the force which is applied to make the object move and it is expressed as:
W = FΔx
Therefore, the relation between force and power is given as:
P = FΔx/ΔT