Work Energy Power Physical work Work W is

Work. Energy. Power

Physical work • Work (W) is defined as the force (F) times the distance (s) moved in the direction of the force (cosΘ) • NB! Θ is angle between the applied force and tirection of motion • If there are no movement in the direction of force, then no work is done • Work is scalar quantity • Work is measured in joules (1 J = 1 Nm=1 kgm 2 s-2)

Work vs Energy • Work done is equal to converted energy • When work is done, energy is converted to different types. • Kinetic energy (Ek or KE) is the energy a body because it is moving • Potential energy (Ep or PE) is the energy stored in a body or in a system due to its position in a force field or due to its configuration – Gravitational potential energy is the energy a body has because of its position in vertical height relative to a given point (height from surface of earth)

Kinetic energy • m – mass of body • v – velocity (speed) of body • Kinetic energy is scalar quantity measured in joules (1 J)

Gravitational potential energy • • m – mass of body g=9. 81 ms-2 – gravitational acceleration Δh – change in height (vertical) Potential energy is scalar quantity measured in joules (1 J)

Conservation of energy • Energy cannot be created or destroyed; only changed form one form to another • There are many different forms of energy: – – – kinetic energy; potential energy; elastic potential energy; heat energy; light energy; sound energy; chemical energy; electrical energy; magnetic energy; nuclear energy; etc

Power • Power (P) is measure how fast work (W) is done or how quickly energy is converted (ΔE): • Δt – is time taken in seconds • Power is scalar quantity measured in watts (1 W=1 Js-1=1 kgm 2 s-3)

Efficiency • Efficiency is a ratio of how much work, energy or power we get out of a system compared to how much is put in • Efficiency is scalar quantity and has no unit! It is measured usually in percentages.

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