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 another point with a convenient change of magnitude and direction. In this article we shall study the terminology associated with the simple machines.
Types of Machine:
The basic machines are
In this article, we shall study levers. Levers are the simplest kind of machine used in daily life.
Principle of Lever:
Lever works on the principle of moments.
This is an expression for mechanical advantage of a lever.
Thus, mechanical advantage of a lever is equal to the ratio of the length of its effort arm to the length of its load arm.
This relation is also known as the law of levers.
Thus, mechanical advantage of lever can be increased by increasing effort arm or decreasing load arm.
Types of Levers:
Depending upon the relative position of the load, the effort and the fulcrum levers have three types: a) Class I levers, b) Class II levers, and c) Class III levers.
Class – I (First Order) Lever:
In this type of levers the fulcrum lies between the load and the effort. It is to be noted that the fulcrum need not be at the midpoint between the load and the effort.
Examples: A see-saw, pliers, scissors, crowbar, Handle of a common water pump, bicycle hand brakes, claw hammer, nodding of human head, etc.
Notes:
Why there is a need of long handles for spanners?
Spanner is a class – I lever and we know if effort arm is greater than load arm, then M.A. > 1. When handle is long, small effort can be used to overcome large loads. Thus with longer handle oar, spanners can be used with less effort.
Why does oar used to row a boat has longer handle?
An oar used to row a boat is Class – I lever and we know if effort arm is greater than load arm, then M.A. > 1. When handle is long, small effort can be used to overcome large loads. Thus with longer handle oar, the boat can be rowed with less effort.
Explain why scissors for cutting cloth may have blades longer than the handles, but shears for cutting metals have short blades and long handles.
The cloth is thin, and can be cut very easily but here gain of speed is required, which is obtained by having mechanical advantage less than one. i.e. by making effort arm of smaller than the load arm. Hence scissors for cutting cloth may have blades longer than the handles.
Metal plates require large force to cut them. Hence here force multiplier is required, which is obtained by having mechanical advantage greater than one. i.e. by making effort arm of scissors larger than the load arm. Hence shears for cutting metal may have short blades and long handles.
Class – II (Second Order) Lever:
In this type of levers the Load is lies between the effort and the fulcrum.
Examples:Diving board, door knob, paddle, nut cracker, wheel barrow, bottle opener, oar of a boat. hand flour grinder,
What is a reason that the handle is provided at the rim of a hand flour mill?
A hand flour mill is a 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.
Examples:Fire tong, boat paddle, Stapler, broom, fishing rod, Ice tong, tweezers, hammer
Characteristics of Class – III Lever:
