Download Work Energy Power

Work
Energy
refers to an activity
involving a force and
movement in the
direction of the force.
A force of 20
Newtons pushing an
object 5 metres in the
direction of the force
does 100 joules of
work.
is the capacity for
doing work. You
must have energy to
accomplish work - it
is like the "currency"
for performing work.
To do 100 joules of
work, you must
expend 100 joules of
energy.
Power
is the rate of doing
work or the rate of
using energy, which
are numerically the
same. If you do 100
joules of work in one
second (using 100
joules of energy), the
power is 100 watts.
Work-Energy Principle
The change in the kinetic energy of an object is equal to the net work done on
the object.
This fact is referred to as the Work-Energy Principle and is often a very useful tool in
mechanics problem solving. It is derivable from conservation of energy and the
application of the relationships for work and energy, so it is not independent of the
conservation laws. It is in fact a specific application of conservation of energy.
However, there are so many mechanical problems which are solved efficiently by
applying this principle that it merits separate attention as a working principle.
For a straight-line collision, the net work done is equal to the average force of impact
times the distance travelled during the impact.
Average impact force x distance travelled = change in kinetic energy
If a moving object is stopped by a collision, extending the stopping distance will
reduce the average impact force.
Gravitational Potential Energy
Gravitational potential energy is energy an object possesses because of its position
in a gravitational field. The most common use of gravitational potential energy is for
an object near the surface of the Earth where the gravitational acceleration can be
assumed to be constant at about 9.8 m/s2. Since the zero of gravitational potential
energy can be chosen at any point (like the choice of the zero of a coordinate
system), the potential energy at a height h above that point is equal to the work which
would be required to lift the object to that height with no net change in kinetic energy.
Since the force required to lift it is equal to its weight, it follows that the gravitational
potential energy is equal to its weight times the height to which it is lifted.
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Kinetic Energy
Kinetic energy is energy of motion. The kinetic energy of an object is the energy it
possesses because of its motion. The kinetic energy of a point mass m is given by
Kinetic energy is an expression of the fact that a moving object can do work on
anything it hits; it quantifies the amount of work the object could do as a result of its
motion. The total mechanical energy of an object is the sum of its kinetic energy and
potential energy.
For an object of finite size, this kinetic energy is called the translational kinetic energy
of the mass to distinguish it from any rotational kinetic energy it might possess - the
total kinetic energy of a mass can be expressed as the sum of the translational
kinetic energy of its centre of mass plus the kinetic energy of rotation about its centre
of mass.
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Kinetic Energy Concept
Kinetic energy is energy of motion. The kinetic energy of an object is the energy it
possesses because of its motion. The kinetic energy of a point mass m is given by:
Internal Energy
Internal energy is defined as the energy associated with the random, disordered
motion of molecules. It is separated in scale from the macroscopic ordered energy
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associated with moving objects; it refers to the invisible microscopic energy on the
atomic and molecular scale. For example, a room temperature glass of water sitting
on a table has no apparent energy, either potential or kinetic . But on the microscopic
scale it is a seething mass of high speed molecules travelling at hundreds of metres
per second. If the water were tossed across the room, this microscopic energy would
not necessarily be changed when we superimpose an ordered large scale motion on
the water as a whole.
U is the most common symbol used for internal energy.
Web sites:
Notes on work, energy and power:
http://hyperphysics.phy-astr.gsu.edu/hbase/work.html
Notes on KE and PE:
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
Internal energy:
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
More notes on energy:
http://www.physicsclassroom.com/Class/energy/U5L1a.html
http://www.physicsclassroom.com/Class/energy/U5L2a.html
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