Page 93 - CITS - WCS - Mechanical

WORKSHOP SCIENCE - CITS

EXERCISE 8 : Simple machines

A simple machine is a mechanical device that changes the direction or magnitude of a force. In general, they can
be defined as the simplest mechanisms that use mechanical advantage (also called leverage) to multiply force.
Usually the term refers to the six classical simple machines that were defined as follows:
Level: A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum.

Wheel and axle: The wheel and axle is a simple machine consisting of a wheel attached to a smaller axle so
that these two parts rotate together in which a force is transferred from one to the other.
Pulley: A pulley is a wheel on an axle or shaft enabling a taut cable or belt passing over the wheel to move and
change direction, or transfer power between itself and a shaft.
Inclined plane: An inclined plane, also known as a ramp, is a flat supporting surface tilted at an angle from the
vertical direction, with one end higher than the other, used as an aid for raising or lowering a load.
Wedge: A wedge is a triangular shaped tool, a portable inclined plane, and one of the six simple machines. It can
be used to separate two objects or portions of an object, lift up an object, or hold an object in place.
Screw: A screw is a mechanism that converts rotational motion to linear motion, and a torque (rotational force)
to a linear force. It is one of the six classical simple machine.

Concept of Mechanical Advantage:
Mechanical advantage is a measure of the ration of output force to input force in a system, used to analyze the
forces in simple machines like levers and pulleys.

Mechanical advantage is also defined as the force created by the machine to the for applied to it. The formula of
mechanical advantage is given as: MA = FB/FA.
The ideal mechanical advantage (IMA), or theoretical mechanical advantage, is the mechanical advantage of a
device with the assumption that its components do not flex, there is no friction, and there is no wear.
If the input effort on a lever is 10 Newtons and the output load is 50 Newtons, what is the mechanical advantage?
The lever helps to multiply a person’s effort to lift the object by almost 5 times. Hence, by using a lever the object
now becomes easier to lift. Also, for example in steering system, the driver applies a relatively small force to
steering wheel and this results in much larger steering force at wheels. Mechanical advantages allows humans
to perform tasks much easier in terms of the force they need to apply,
Velocity Ratio: Velocity ration is the ration of the velocity at which effort is applied on a machine to the velocity
at which load moves.
The ratio of the velocity of effort to the velocity of the load is called Velocity Ratio (VR) i.e., Velocity Ratio (VR) =
(Velocity of effort) / (Velocity of load) So, Velocity ratio (VR) = V1/V2.
The ratio of the distance moved by the point at which the effort is applied in a simple machine to the distance
moved by the point at which the load is applied, in the same time. In the case of an ideal (frictionless and
weightless) machine, velocity ratio = mechanical advantage.

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