Defination of Mechanical Principles, Force & Gravity

Mechanical Principles:

Mechanical Principles are utilized in exercise therapy are defined and ensure that they understood and applied correctly.


— Force is that which alters a body from its state of rest or its uniform motion in a straight line. It can accelerate objects
Application of force applied to a body is specified by:
—The direction of the force. The magnitude of the force.The arrow, represents the point of application of the force

—Force is measured by the unit Newton (N)
—A force that causes an object with a mass of 1 kg to accelerate at 1 m/s is equivalent to 1 Newton.

Principles of Force

—A single force applied to a body, which is free to move. Leads to movement in direction of the force
—Two equal forces acting at a common point and in opposite directions will result in a state of equilibrium
E.x. Two people pulling a rope in a tug of war

—If they both pull with the same force it will remain equal.Two unequal forces acting at a common point and in opposite directions
—Result in movement in direction of the greater force
E.x. If one side pulls with more force it results in them winning the tug of war

The magnitude of the force producing this movement  being equal to the difference between the magnitudes of two unequal forces which oppose each other. physiotherapists work involves application of force!

Force and its Application

Two forces acting at an angle to each other can be compounded to produce a force.
E.x.  Deltoid muscle contraction during shoulder abduction
Anterior and posterior muscle fibres being compounded to work with middle deltoid muscle fibres to produce greater force.Two unequal forces acting at different points, in opposite directions produce rotation of  a body
E.x. Trapezius muscle and serratus anterior contract to rotate the scapula


Gravity is the force by which all bodies are attracted to the earth.
Newton’s laws:
Force of attraction exists between all material objects.
—Magnitude of this attraction is directly proportional to mass of each body. Inversely proportional to the square distance between them

Gravitational attraction of the earth for every body is directed to earths centre. Force of gravity acts continuously on the human body. If the force is un opposed the body will fall to the ground
—Gravity is counter balanced by equal force or opposite to it

An isometric muscle contraction
—If gravity is opposed by a greater force, movement will occur in that direction
E.x.  Movement in the body
—Standing position the heels can be raised from the ground by contraction of calf muscles working in opposition to the resistance of gravity


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