Subscribe For Free Updates!

We'll not spam mate! We promise.

2012-04-20

Machines | X – Class Physics Notes


Chapter-09

DEFINITIONS

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. 

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. 
M.A = (output/Input) * 100 

4. Input
Input is the work done on
 the machine. 

5. Output
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
 

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
 

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 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.

Socializer Widget By Funny And Amazing
SOCIALIZE IT →
FOLLOW US →
SHARE IT →

0 comments :

Post a Comment