Transcript Work and Energy - IES Guillermina Brito

Work and Energy
mechanical work
mechanical energy
Work
The amount of work depends on:
1. The force you have to exert
2. The distance moved in the direction of the force
Work done by a force =
(joule, J)
force
x distance moved in direction of force
= (newton, N) x
(metre, m)
Example:
Since both force and displacement are in the same direction, this would give a work
of 20 Joules.
W = 10 N x 2 m = 20J
Work and Energy
Amount of work done = amount of energy transferred
Changing their gravitational
potential energy
Changing their kinetic energy
Changing their gravitational potential energy
Gravitational
potential
energy is energy stored
within a physical system
as a result of the height
on Earth surface.
Ep = m · g · h
work done by a force =
gravitational potential energy =
Ep
=
force
x distance moved in direction of force
weight
x
m·g ·h
vertical height difference
Changing their kinetic energy
Ec 
1
 m  v2
2
The kinetic energy of an object is the energy which it possesses due to its motion.
work done by a force =
force
1
kinetic energy   mass  speed
2
2
x distance moved in direction of force
1
Ec   m  v 2
2
Example:
If vo = 0 m/s and its mass is 4 kg then the trolley has a final velocity of
1
Ec   m  v 2
2
30 
1
 4  v2
2
v2 
30
 15
2
v  3,87 m
s
Example:
mechanical energy
and
law of conservation of energy
Mechanical energy describes the sum of potential energy and kinetic energy present
in the components of a mechanical system.
E m = Ec + Ep
The law of conservation of energy is an empirical law of physics.
It states that the total amount of energy in an isolated system remains constant over time.
In mechanics, conservation of energy is usually stated as
Em1 = Em2
Ec1 + Ep1 = Ec2 + Ep2
Example:
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Example: