A Simple Machine is a device that makes our work easier, change the
direction of the force and works with more efficiently.
A simple rod, knife, scissor and a wheelbarrow are the example of simple
machines. They help us to do our work easily and quickly.
When we work on the machine, mechanical energy of the machine changes
and that's the force which does the work.
The ratio of load lifted by a simple machine to the effort
applied on it is called
MA = Load (L) / (Effort)E
It does not have any unit since it is the ration of two
A man lifted a load of 600 N using a simple machine. If he
applied 200 N
effort, then the mechanical advantage of this machine is (M.A) =
600 / 200 = 3.
Note: The Mechanical Advantage more than 1 multiplies Effort,
less than 1 speeds the doing works, and equal to 1 makes the
work easy and change the direction of effort.
Velocity Ratio (V.R.):
The ratio of velocity of effort to the velocity of load is
called the velocity ratio of the simple machine.
Velocity Ratio = (Velocity of effort) / (Velocity of
if load and effort cover certain distance in the same time,
V.R = (Distance covered by effort / time) / (Distance
covered by load / time)
V.R = (Distance covered by effort ) / (Distance covered by
So, V.R = (Effort Distance) / (Load Distance)
So, Velocity ratio may also be defined as the
ratio of distance covered by effort to the distance covered
It also have no unit since it is the ratio of two
Note: Velocity ratio of simple machine is always more then
mechanical advantage because there is no effect of friction in
VR but effect can be seen in MA.
The percentage ratio of output work to the input work of a
simple machine is called efficiency.
An ideal or perfect machine has output work equal to input
work and its efficiency is 100% but, in practical liofe it
is impossible, no any machine has 100% efficiency because
there is always some losses of energy due to friction.
Relation Between M.A., V.R., and η : Efficiency(η) =(MA) / (VR) × 100%
Answer: what does it mean, A machine has 70%
Simple Machine is of Six types:
Lever: A lever is a bar
which can turn about on one point. The
point is called a fulcrum, the force we use on the lever is
called a effort, the weight we try to lift or move it is called
Lever are further classified into three types:
A) First Class Lever: In the first class lever, the fulcrum
is between the load and the effort.
Some common first class levers are see-saw, crowbar, pliers,
B) Second Class Lever: In the second class lever, the fulcrum
is at one end and the load lies between the effort and
Some common second class levers are stapler, botle opener, lemon
C) Third Class Lever: In the third class lever, the effort
lies between load and fulcrum.
Some common third class levers are broom, our arms, etc.
It is a circular disc having groove made on its
circumference to pass rope or string.
It is made by wood or metal or hard substances.Its uses is to
lift a heavy load of greater height.
Like: used in construction site, pulling of water from well,
Velocity ratio (V.R.) = The number of rope segments used to hold
= The number of pulleys used
In a single movable pully the Velocity
Ratio(VR) is two.
Wheel and Axle:
It consists of two co-axial cylinders of different
diameters. The cylinder having larger diameter is called
wheel whereas the cylinder having smaller diameter is called
The effort is applied in wheel and they work jointly. String
roller of a kite, knob of a door etc are the example of wheel
and axle. It is used to lift heavy loads.
The ratio of radius of wheel to the radius of axle is called
velocity ratio of the wheel and axle.
V.R. = (Radius of wheel R) / (Radius of axle r)
A slanted surface made by a plank of wood or metal sheet is
called Inclined Plane.
Heavy loads can be pulled or pushed up by applying little effort
along with it. It makes our work easier by magnifying force. a
wooden plank used to load or unload truck, steep road, staircase
etc are the examples of Inclined plane.
Mechanical advantage in inclined plane is also the ratio of
load lifted to the effort applied.
M.A = Load / Effort
The velocity ratio in the inclined
plane is the ratio of length of slope
to the vertical height of the
V.R = (Length of the slope) / (Height of the Inclined
V.R = d / h
Moment of the force may be defined as the product of
the force and its
perpendicular distance of the line of action from the axis
Moment = f × d
Its unit is Nm
Laws of Moment:
Law of moment states that, “in the equilibrium
condition the sum
of clockwise moments about a point must be equal to the sum of
anticlockwise moments about the same point.”
You felt easy to apply force at the end of the
spanner to unscrew
the nut, why?
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