Work and Energy concepts

1. PHYSICS CHP-11
WORK AND
ENERGY

2. WHAT IS WORK......
SCIENTIFICALLY
• Whenever a force is applied on an object and displacement is achieved
is the scientific definition of work
• Sitting and studying is not work whereas pushing a crate is
classified as work

3. THE FORMULA OF
WORK
• How was the formula for work derived ?
• The formula for work is defined as the amount of force
applied
multiplied by the displacement of the object
W =
Fd
• The S.I unit for work is Joule

4. Can work be negative or
even 0?
When is work positive
?
When and can work be
negative?
Can work be zero ? 0
1
-1

5. Energ
y
What is energy ?
Energy is the capacity to do
work.
Energy can change its form
from kinetic to potential
etc.
If an object does work it is said to lose energy but if an object
has not done work yet it has the capability to do work or
it has energy.
Lets see the different forms of energy
Quick question: what is cos theta

6. Kinetic
Energy
What defines Kinetic energy?
Kinetic energy is the energy possessed by an object due to its
speed or motion
To derive the formula
W=Fs
W = ma*s
W = ma* v^2 - u^2 / 2a
W = 1/2 mv^2 considering u to be zero
as energy is just the capacity to do work
Ek = 1/2 mv^2

7. Potential
Energy
What is potential energy?
It is the energy gained due to configuration or height
Derivation for potential energy
W=fs
W=mg
As potential energy is calculated with height s becomes h or height
Ep=mgh

8. Law of conservation of
energy
Law of conservation of energy states that energy can neither be created
or destroyed in any reaction or action except for nuclear reactions.
So where does the energy go once the object has carried out the task?
The total energy stays the same

9. Power
Power can be described as the rate of doing work
so power measures the speed of doing work
The formula of power
:
P=W/t
Power is measured in watts to pay respects to the
great scientist james watt.
1kw=1000watt
1kw = 1j per s
as watt can be described as joules per unit time.

10. Commercial unit of
energy
The commercial unit of energy is used in everyday to calculate energy as the
amount used is massive
Energy is calculated in KwH which is equal to one unit
There is a device like so to calculate energy.

11. Practice
Questions
Q1) What is the formula for kinetic energy?
Q2) What is the main statement of law of conservation of
energy
Q3) Define 1J of work
Q4) When can we say that work is done?