work in physics
Post on 25-May-2015
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Q. Which agent causes or tends to cause motion in a
body?
A. It is the “force” which causes or tends to cause
motion in a body.
F
Q. What is force ?
A. The agent which ;
Stops or tends to stop the motion
Produces or tends to produce the motion
OR
Q. Which path is the shortest in the figure shown?
A. 2nd path is the shortest one.
A B
1st path
2nd path
3rd path
Q. What does the shortest path called?
A. Displacement
Q. Which quantity depends upon force and
displacement?
A. Work depends upon force and displacement.
WORK
Definition
Mathematical Form
Unit
Cases of Work
WORK In general work is said to be done when
someone pushes against a brick wall and
does not able to move it
A boy studies a book for a few hours
But in Physics work is defined differently
Q. What is work?
A. Work is said to be done when a force acts on a
body and moves it through a certain displacement.
WORK
dWork done by the Force F
m mF
Mathematical Form:
WORK
dWork done by the Force F
m mF
If force is applied on a body and it moves the
body through a displacement ‘d ’, then the work 'W' is
defined by the relation
W = F. d
We have already studied scalars and vectors.
Q. What is the nature of work?
A. Work is a scalar quantity.
WORK
If the force makes an angle θ with the
direction of the displacement then,
We take the component of the force in
the direction of the displacement
WORK
Unit of work:
The SI unit of work is joule (J).
One Joule
When a force of one Newton moves a body
through a distance of one meter in the direction of
force, then the work done is equal to one joule.
WORK
Positive Work
CASES OF WORK
When force and displacement are in the same
direction
Then = 0°
W = F d cos 0°
= F d x 1
= F d
In this case work done is maximum and is
equal to the product of the magnitude of force and
displacement.
CASES OF WORK
Positive Work
Example
Work done by the Force
m m
F
CASES OF WORK
d
Zero Work
When force is perpendicular to the
displacement
Then = 90°
W = F S cos 90°
= F x 0
= 0
In this case work done is zero.
CASES OF WORK
Example
CASES OF WORK
When force and displacement are in the opposite direction
Then = 180°
W = F d cos 180°
= F d x (-1) cos 180° = -1
W = - F d
CASES OF WORK
Negative Work
Condition for Negative work
d
W
CASES OF WORK
Given Data
Applied force = F = 300 N
Displacement covered by body = d = 10m
Angle between force and
displacement = = 60o
Work done = w = ?
ACTIVITY
Q. What is the definition of work?
A. It is the product of displacement and component
of force along displacement.
Q. What is the unit of work?
A. The unit of work is “joule”.
WORK
Q. Give an example of positive work?
A. Pushing something horizontally is an example of
positive work.
Q. Give an example of negative work?
A. Lifting something vertically upwards is an example
of negative work.
WORK
Q. Give an example of zero work?
A. If a person holds the pail in his hand and walks
along a level surface.
Q. Explain the given figure?
CASES OF WORK
THANK YOU
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