Chapter-09
DEFINITIONS
1. Machine
1. Machine
A machine
is a device by means of which useful work can be performed conveniently and it
can also transfer one form of energy into another form of energy.
2. Mechanical Advantage
The ratio between the resistance or weight to the power applied in a machine is called the mechanical advantage of that machine. It is denoted by M.A.
The ratio between the resistance or weight to the power applied in a machine is called the mechanical advantage of that machine. It is denoted by M.A.
M.A. = Weight over-comed by
Machine/ Force Applied on the
Machine
3. Efficiency
The ratio between the useful work done and the work done on the machine is called efficiency.
The ratio between the useful work done and the work done on the machine is called efficiency.
M.A = (output/Input) * 100
4. Input
Input is the work done on the machine.
Input is the work done on the machine.
5. Output
Output is useful work done by the machine.
LEVER
Definition
Output is useful work done by the machine.
LEVER
Definition
Lever is
the simplest machine in the world. It is a rigid bar, which can be rotated
about a fixed point.
Principle
of Lever
In the
lever the moment P acts opposite to that of work W. It means that force F tends
to rotate the lever in one direction which the wight W rotates in opposite
direction. If the magnitude of these moments acting in opposite direction is
equal, then the lever will be in equilibrium. It means that:
Moment of P = Moment of W
Moment of P = Moment of W
Mechanical Advantage
We know that according to Principle of Lever:
Moment of P = Moment of W
=> Force * Force Arm = Weight * Weight Arm
P * AB = W X BC
AB/BC = W/P
Hence,
M.A = W/P = AB/BC = Weight Arm/ Force Arm
KINDS OF LEVER
1. First Kind of Lever
In the
first kind of lever, the fulcrum F is in the between the effort P and Weight W.
Examples
- Physical Balance
- Handle of Pump
- Pair of Scissors
- See Saw
2. Second Kind of Lever
In the
second kind of lever, the weight W is in between the fulcrum F and effort P.
Examples
- Door
- Nut Cracker
- Punching Machine
3. Third Kind of Lever
In the
third kind of lever, the effortP is in between the fulcrum F and weight W.
Examples
- Human forearm
- Upper and Lower
Jaws in the Mouth.
- A Pair of
Forecepes
INCLINED PLANE
Definition
A heavy load can be lifted more
easily by pulling it along a slope rather than by lifting in vertically. Such a
slope is called an Inclined Plane.
Mechanical Advantage
M.A = W/P = l/h = Length of Inclined Plane/Perpendicular Height
M.A = W/P = l/h = Length of Inclined Plane/Perpendicular Height
Pulley
A pulley consists of a wheel mounted on an axle that is fixed to the framework called the block. The wheel can rotate freely in the block. The groove in the circumference prevents the string from slipping.
Fixed
Pulley
If the
block of the pulley is fixed then it is called a fixed pulley.
Mechanical Advantage of Fixed Pulley
In a fixed
pulley, the force P is the applied force and weight W is lifted. If we neclect
the force of friction then:
Load = Effort
In the given case:
Load = W * Load Arm
Load = W * OB
Also,
Effort = P * Effort Arm
Effort = P * OA
So,
W*OB = P*OA
=> W/P = OA/OB
But, OA = OB, then
M.A = W/P = OB/OB
M.A = 1
Moveable Pulley
In the given case:
Load = W * Load Arm
Load = W * OB
Also,
Effort = P * Effort Arm
Effort = P * OA
So,
W*OB = P*OA
=> W/P = OA/OB
But, OA = OB, then
M.A = W/P = OB/OB
M.A = 1
Moveable Pulley
In this
pulley, one end of the rope that is passing around the pulley is tied to a firm
support and effort P is applied from its other end. The load and weight to be
lifted is hung from the hook of block. In this system, the pulley can move.
Such a pulley is called moveable pulley.
Mechanical Advantage of Moveable Pulley
In an
ideal system of a moveable pulley, the tension in each segment of the rope is
equal to the applied effort. As two segments support the weight, the ffort
acting on the weight W is 2P. Therefore, according to the principle of lever:
W * Radius of the Wheel = 2P *
Radius of the Wheel
=> 2P = W
The Mechanical Advantage is given by:
M.A = W/P
M.A = 2P/P
=> M.A = 2
Hence, the mechanical advantage of a moveable pulley is 2.
=> 2P = W
The Mechanical Advantage is given by:
M.A = W/P
M.A = 2P/P
=> M.A = 2
Hence, the mechanical advantage of a moveable pulley is 2.
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