Simple Machines

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Simple Machine:

  • A simple machine is a mechanical device that makes our life easier. If a force is applied at one point, the simple machine transmits it to the another point with a convenient change of magnitude and direction.

Types of Machines:

  • The six basic machines are a)  Lever b)  Inclined plane c)  Pulley (Special case of levers) d) Wheel and axle (Special case of levers) e)  Wedge (Special case of inclined plane) f)  Screw (Special case of inclined plane)

Functions of Simple Machines:

  • Applying force at convenient point. Instead of applying force directly to the wheels of a bicycle, it is easier and more convenient to apply it to the pedals.
  • Applying force at convenient direction. It is difficult to lift a bucket full of water directly, but the task becomes very easy if the force is applied in downward direction using a pulley.
  • By applying small effort to lift large loads. In such case machine is said to be used as force multiplier. A screw jack used to lift a car or a truck.
  • To change speed of motion of a body.  In such case machine is said to be used as speed multiplier. Gears in automobile are used to change the speed of the automobile.

Important Terms:

Load (L):

  • A resistive force to be overcome by a machine is called a load. Its S.I. unit is newton (N)

Effort (E):

  • An external force applied to a simple machine to overcome a load is called an effort. Its S.I. unit is newton (N)

Mechanical Advantage (M.A.):

  • The ratio of load (L) to overcome to the magnitude of the effort (E) is called a mechanical advantage. It is also called as leverage.

Simple Machines 01

  • As it is ratio of same type of physical quantities, the mechanical advantage is unit less and dimension less quantity.

Velocity Ratio:

  • The ratio of a distance traveled by the effort to the distance traveled by the load in given time is called velocity ratio.

Simple Machines 02

  • As it is ratio of same type of physical quantities, the velocity ratio is unit less and dimension less quantity.

Work Input:

  • The energy supplied to a machine is called work input. Its S.I. unit is joule (J).
  • Work Input = Effort (E) X Distance traveled by an  effort (s)

Work Output:

  • The useful work done by a machine is called work output. Its S.I. unit is joule (J).
  • Work Output = Load (L) X Distance traveled by a load (l)

Efficiency :

  • The ratio of the useful work output to the actual work input of the machine is called efficiency.

Simple Machines 03



Terminology of Levers:

Lever: 

  • A rigid object that is used with an appropriate fulcrum point to multiply the mechanical force that can be applied to another object.

Fulcrum:

  • It is an axis about which the lever turns and passes through a point of lever.

Effort Arm (E.A.):

  • The distance between the effort and fulcrum is called an effort arm.

Load Arm (L.A.):

  • The distance between the load and fulcrum is called an load arm.

Principle of Lever:

Levers 01



This is an expression for mechanical advantage of a lever.

Example – 1:

  • A machine has mechanical advantage 5. It raises load of 25 N. Calculate the minimum effort required.

Solution:

Levers 02

Example – 2:

  • The efficiency of a machine is 50 %. If 300 J of energy given to the machine. What is its output?

Solution:



Levers 03

Types of Levers:

Depending upon the relative position of the load, the effort and the fulcrum levers have three types.

Class – I (First Order) Lever:

  • In this type of levers the fulcrum lies between the load and the effort.

Levers Class I 01

  • Examples:A see saw, pliers, scissors, crowbar, Handle of common water pump, bicycle hand brakes, claw hammer,

Levers Class I 02

Levers Class I 03



Characteristics of Class – I Lever:

  • Fulcrum lies in between load and effort.
  • If E.A. > L.A. then M.A. > 1 If E.A. < L.A. then M.A. < 1 If E.A. = L.A. then M.A. = 1
  • This type of lever acts as force (effort) multiplier.

Why there is a need of long handles for spanners?

  • Spanner is a class – I lever and we know that for class – l and if effort arm is greater than  load arm. Hence M.A. > 1.
  • To have more mechanical advantage effort arm (length of handle) of spanner should be increased. When handle is long, small effort can be used to overcome large loads.


Class – II (Second Order) Lever:

  • In this type of levers the Load is lies between the effort and the fulcrum.

Levers Class II 01

  • Examples:Diving board, door knob, paddle, nut cracker, wheel barrow, bottle opener, oar of a boat. hand flour grinder,

Levers Class II 02

Levers Class II 03

Characteristics of Class – II Lever:

  • Load lies in between fulcrum and effort.
  • Effort arm is always greater than the load arm, hence the M.A. of class – II lever is always greater than 1.
  • This type of lever acts as force (effort) multiplier.

What is a reason that the handle is provided at the rim of a hand flour mill?

  • Hand flour mill is class – II lever, and we know that for class – II lever, the effort arm is always greater than  the load arm. Hence M.A. > 1. Thus more mechanical advantage can be obtained by increasing effort arm.
  • It can be done by providing the handle at the rim of the hand flour mill. Thus applying small effort, large loads can be overcome.

Class – III (Third Order) Lever:

  • In this type of levers the effort is applied between the load and the fulcrum.

Levers Class III 01

  • Examples:Fire tong, boat paddle, Stapler, broom, fishing rod, Ice tong, tweezers, hammer

Levers Class III 02



 

Characteristics of Class – III Lever:

  • Effort lies in between fulcrum and load.
  • Effort arm is always less than the load arm, hence the M.A. of class – III lever is always less than 1.
  • This type of lever acts as speed multiplier.

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