Work and Energy
When a force act on an object and the object move through some distance in the
direction of the force
Symbol of work =w
Force and displacement
Same or not
Mathematically: work done is product of force and displacement.
Work done = force X displacement
W= Fs (for same direction)
Work done is a scalar quantity.
S.I unit =joule (J) or N X m
Joule: when a force of 1N is applied on a body to displace it by 1m then the work
done is 1joule. 1joule = 1N X 1m
Work is done only if
A force is applied to an object.
The object is displaced from one point to another.
When force and displacement are not in same direction.
Trigonometric function
Direction f cos ϴ=horizontally
Rotation f sin ϴ =vertically
Magnitude
∴ F sinϴ and f cosϴ is component of
W= fs cosϴ
Cos ϴ 0º 30º 45º 60º 90º
1 √3/2 1/√2 ½ 0
Types of work done
Positive Negative Zero
, Positive work done: work done is positive when a force acts in the direction of
motion of the body.
Angle between force and displacement or motion. So, ϴ=0º
Formula: w = Fs cos ϴ
W= Fs cos 0º
W= +FS
Positive work increases the speed of any object.
E.g.: 1.Push and pull of the door.
2. Kicking the football.
3. Throwing of a ball upward by any person.
Negative work done: work done is negative when a force acts in the opposite
direction of motion of the body.
Angle between force and displacement. So, ϴ=180º
Formula: w=fs cosϴ
W=fs cos 180º
W= fs (-1)
W= -fs
Negative work decreases the speed of any object.
It’s follow the 3rd law of motion (2as=v²-u²)
E.g.: 1.Throwing a ball upward under the gravity.
2. Friction force and sliding book.
3. Compressed spring (relative force).
4. Braking system.
Zero work done: if and displacement are at right angle perpendicular with each
other.
Angle between force and displacement is ϴ=90⁰ f
Formula: w=fs cosϴ m
W=fs cos 90⁰
W=fs 0
W=0
It will not affect the motion of the body along the displacement. But the object
at rest.
When a force act on an object and the object move through some distance in the
direction of the force
Symbol of work =w
Force and displacement
Same or not
Mathematically: work done is product of force and displacement.
Work done = force X displacement
W= Fs (for same direction)
Work done is a scalar quantity.
S.I unit =joule (J) or N X m
Joule: when a force of 1N is applied on a body to displace it by 1m then the work
done is 1joule. 1joule = 1N X 1m
Work is done only if
A force is applied to an object.
The object is displaced from one point to another.
When force and displacement are not in same direction.
Trigonometric function
Direction f cos ϴ=horizontally
Rotation f sin ϴ =vertically
Magnitude
∴ F sinϴ and f cosϴ is component of
W= fs cosϴ
Cos ϴ 0º 30º 45º 60º 90º
1 √3/2 1/√2 ½ 0
Types of work done
Positive Negative Zero
, Positive work done: work done is positive when a force acts in the direction of
motion of the body.
Angle between force and displacement or motion. So, ϴ=0º
Formula: w = Fs cos ϴ
W= Fs cos 0º
W= +FS
Positive work increases the speed of any object.
E.g.: 1.Push and pull of the door.
2. Kicking the football.
3. Throwing of a ball upward by any person.
Negative work done: work done is negative when a force acts in the opposite
direction of motion of the body.
Angle between force and displacement. So, ϴ=180º
Formula: w=fs cosϴ
W=fs cos 180º
W= fs (-1)
W= -fs
Negative work decreases the speed of any object.
It’s follow the 3rd law of motion (2as=v²-u²)
E.g.: 1.Throwing a ball upward under the gravity.
2. Friction force and sliding book.
3. Compressed spring (relative force).
4. Braking system.
Zero work done: if and displacement are at right angle perpendicular with each
other.
Angle between force and displacement is ϴ=90⁰ f
Formula: w=fs cosϴ m
W=fs cos 90⁰
W=fs 0
W=0
It will not affect the motion of the body along the displacement. But the object
at rest.
