Transcript Work. Energy. Power

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 (1J = 1Nm=1kgm2s-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 (1J)
Gravitational potential energy
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m – mass of body
g=9.81 ms-2 – gravitational acceleration
Δh – change in height (vertical)
Potential energy is scalar quantity measured
in joules (1J)
Conservation of energy
• Energy cannot be created or destroyed; only
changed form one form to another
• There are many different forms of energy:
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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
(1W=1Js-1=1kgm2s-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.
SAMPLE 1
SAMPLE 2
Sample 3
Sample 4 (1/2)
Sample 4 (2/2)
Sample 5
Sample 6