Shruthi.A class 9"a" chennai public school thirumazhisai

1. WORK
AND
ENERGY

2. WORK
What is
work?
There is a
difference in
the way the
term “work”
in day to day
life and the
way we use
in science

3. WHAT IS WORK?

4. A force is said to do work .
If, when acting on a body, there is a displacement of the
point of application in the direction of the force.
For example, when a ball is held above the ground and
then dropped, the work done on the ball as it falls is
equal to the weight of the ball (a force) multiplied by the
distance to the ground (a displacement).
The term work was introduced in 1826 by the French
mathematician Gaspard-Gustave Coriolis as
"weight lifted through a height", which is based on the
use of early steam engines to lift buckets of water out of
flooded ore mines. The SI unit of work is the newton-
metre or joule (J).

5. ENERGY
energy is a property of objects which can be transferred to other objects
or converted into different forms, but cannot be created or destroyed.The "ability of a
system to perform work" is a common description, but it is difficult to give one single
comprehensive definition of energy because of its many forms. For instance, in SI
units, energy is measured in joules, and one joule is defined "mechanically", being the
energy transferred to an object by the mechanical work of moving it a distance of
1 meter against a force of 1 newton. However, there are many other definitions of
energy, depending on the context, such as thermal energy, radiant energy,
electromagnetic, nuclear, etc., where definitions are derived that are the most
convenient.
Common energy forms include the kinetic energy of a moving object, the radiant
energy carried by light, the potential energy stored by an object's position in a
force field(gravitational, electric or magnetic), elastic energy stored by stretching solid
objects, chemical energy released when a fuel burns, and the thermal energy due to
an object's temperature. All of the many forms of energy are convertible to other kinds
of energy, and obey the law of conservation of energy which says that energy can be
neither created nor be destroyed; however, it can change from one form to another.

6. For "closed systems" with no external source or sink of
energy, the first law of thermodynamics states that a
system's energy is constant unless energy is transferred
in or out by mechanical work or heat, and that no energy
is lost in transfer. This means that it is impossible to
create or destroy energy. The second law of
thermodynamics states that all systems doing work
always lose some energy as waste heat. This creates a
limit to the amount of energy that can do work by a
heating process, a limit called the available energy.
Mechanical and other forms of energy can be
transformed in the other direction into thermal
energy without such limitations. The total energy of a
system can be calculated by adding up all forms of
energy in the system.

7. Examples of energy transformation include generating electric energy from heat
energy via a steam turbine, or lifting an object against gravity using electrical
energy driving a crane motor. Lifting against gravity performs mechanical work on
the object and stores gravitational potential energy In the object. If the object falls to
ground, gravity does mechanical work on the object which transforms the potential
energy in the gravitational field to the kinetic energy released as heat on impact
with the ground. Our Sun transforms nuclear potential energy to other forms of
energy; its total mass does not decrease due to that in itself (since it still contains
the same total energy even if in different forms), but its mass does decrease when
the energy escapes out to its surroundings, largely as radiant energy.
Mass and energy are closely related. According to the theory of mass–energy
equivalence, any object that has mass when stationary in a frame of reference
(called rest mass) also has an equivalent amount of energy whose form is
called rest energy in that frame, and any additional energy acquired by the object
above that rest energy will increase an object's mass. For example, if you had a
sensitive enough scale, you could measure an increase in mass after heating an
object.
Living organisms require available energy to stay alive, such as the energy humans
get from food. Civilization gets the energy it needs from energy resources such
as fossil fuels. The processes of Earth's climate and ecosystem are driven by the
radiant energy Earth receives from the sun and the geothermal energy contained
within the earth.

8. WORK AND ENERGY
The work done by a constant force of
magnitude F on a point that moves a displacement
(not distance) s in the direction of the force is the
product,
For example, if a force of 10 newtons (F = 10 N)
acts along a point that travels 2 metres (s = 2 m),
then it does the work W = (10 N)(2 m) = 20 N m =
20 J. This is approximately the work done lifting a
1 kg weight from ground to over a person's head
against the force of gravity. Notice that the work is
doubled either by lifting twice the weight the same
distance or by lifting the same weight twice the
distance.

9. Work is closely related to energy. The law of
conservation of energy states that the
change in total internal energy of a system
equals the added heat, minus the work
performed by the system (see the first law of
thermodynamics),
where the symbol indicates that heat (Q)
and work (W) are inexact differentials.

10. From Newton's second law, it can be
shown that work on a free (no fields),
rigid (no internal degrees of freedom)
body, is equal to the change in kinetic
energy of the velocity and rotation of
that body,

11. The work of forces generated by a potential function is
known as potential energy and the forces are said to
be conservative. Therefore, work on an object that is
merely displaced in a conservative force field, without
change in velocity or rotation, is equal to minus the
change of potential energy of the object,
These formulas demonstrate that work is the energy
associated with the action of a force, so work
subsequently possesses the physical dimensions, and
units, of energy. The work/energy principles discussed
here are identical to Electric work/energy principles.