Скачать или смотреть Work energy power||ICSE class 8 physics chapter 4

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What is work its unit.

Everyday meaning of work is some activity that requires physical or mental effort. But according to physics, the definition of work is more precise and unambiguous. In Physics, if a force displaces an object, the work is said to be done.

The SI unit of work done = Newton(N) X metre(m) = joule(J)

Energy is the capacity to do work. Energy is the cause and work is an effect. Therefore both work and energy have the same units, which is joule (J) in the SI system and erg in the CGS system. Kinetic energy and potential energy are the two main types of energy.
Power is the work done in a unit of time. In other words, power is a measure of how quickly work can be done.
The unit of power is the Watt = 1 Joule/ 1 second.

In this chapter, we will learn more about work, energy, power, their measurements, and units.

Work done by a constant force
Work is said to be done only when the force is applied on a body makes the body move
The amount of work done by a force is equal to the product of the force and the displacement of the point of application of the force in the direction of force
W = F × S, It is a scalar quantity
Note:

The amount of work done by a force depends on, the magnitude and direction of the force & displacement it produces, If a force acts on a body and the body does not move, no work is done
Expression of work
Work done W = force × component of displacement in the direction of force, W = F × S cos θ
If the displacement is in the direction of the force i.e., θ=0∘, then cosθ=cos0∘= 1, W = F × S, The work done is maximum and positive
Different conditions
Condition for the work done by a force to be zero
When there is no displacement i.e., S = 0, force i.e. = 90∘
If the displacement is in a direction opposite to the force, i.e., θ=180∘
W = F × S cos 180∘ = – F × S, Work done is negative
Work done by the force of gravity
W = F × S = mgh
The work done by the force of gravity is the same whether a man comes down from a certain height (h) using a staircase or along the slope or he comes down from the same height using a lift or elevator
Unit of work
S.I. unit of work is newton metre (Nm) or joule (J)
1 J is the amount of work done on an object when a force of 1N displaces it by 1m along the line of action of force
C.G.S unit of work is dyne centimetre or erg, 1 J = 107 erg
Power
Power is defined as the rate of doing work or the rate of transfer of energy
P = wt ⇒ P = F × v = force × average speed
The S.I. unit of power is watt and its symbol is W, 1 watt = 1JouleSec or 1W = 1Js−1, 1 H.P. = 746 W = 0.746 kW
The C.G.S unit of power is erg per second (erg s−1), 1W = 1Js−1 = 107 erg s−1
Factors on which power spent by a source depends on:

The amount of work done by the source.
The time taken by the source to do the said work.