WORK, ENERGY AND
MACHINES
ASP Physics
OBJECTIVES
(By the end
of this
presentation
students are
able to-)
Identify
Derive
Identify work as a product of scalar multiplication of force
and displacement.
Derive the formula for work.
Identify
Identify joule as the SI unit and deduce its equivalent
base unit as N.m
Understand
Understand that the angle between force and
displacement determines the value of work and also
whether the work is negative or positive.
WORK
■ When a force is applied through a displacement, work is done on the system.
■ Work can thus be defined as the product of force and displacement.
W= Fd
where- W- Work Done
F- Force exerted on system
d- Displacement
■ In the following situations is work being done?
1)
Teacher pushing hard on the wall of the classroom.
2)
A book falls off the table and free falls to the ground.
3)
A car is being stopped by pushing against its direction of motion.
4)
School bag is being dragged by a student to her desk.
SI Unit of Work
■ The SI unit of work is joule (J).
■ One joule of work is said to be done if a force of 1 newton acts on a system and
causes a displacement of 1 m.
■ Thus the base unit of joule is N.m
■ Think over this…..
Q. What if a force of 2 N acts on the system displacing it by 2m? Will the work be 1 N?
watts

Used to measure power of light
bulbs and small appliances

An electric bill is measured in
kW/hrs.
 1 kilowatt = 1000 W
Horsepower (hp) = 745.5 watts

Traditionally associated with engines. (car,motorcycle,lawn-mower)

The term horsepower was developed to quantify power. A strong horse could move a
750 N object one meter in one second.
750 N
Power from Velocity- Force Graph
■ Area under the graph
gives the power.