fundamentals of Force , Motion and Work.ppt

Motion - Introduction
 It is defined as a change of position with respect to time
and surrounding
 The objects that do not change their position are said to be
at rest.
 Motion and Rest are relative phenomena.
Types of Motion
Linear motion: Motion along a straight line.
Circular motion: Motion along a circular path.
Oscillatory motion: Repetitive to and fro motion of an object
at regular intervals of time.
Random motion: Motion of the object which does not fall into
any of the above categories.

Uniform and Non-uniform Motion
Uniform motion
If any object covers equal distance at equal interval of time.
Non-uniform motion
If any object covers unequal distances in equal intervals of
time.

Distance and Displacement
Distance
 The actual length of the path travelled by a moving
body irrespective of the direction is called the distance.
 It is measured in metre in SI system.
 It is a scalar quantity having magnitude only.
Displacement
 It is defined as the change in position
of a moving body in a particular
direction.
 It is a vector quantity having both
magnitude and direction.
 It is also measured in metre in SI
system.

Speed
 Speed is the rate of change
of distance or the distance travelled
in unit time.
 It is a scalar quantity.
The SI unit of speed is ms-1
 Speed = Distance travelled / Time taken
Velocity
 Velocity is the rate of change of
displacement.
 It is the displacement in unit time.
 It is a vector quantity.
 The SI unit of velocity is ms-1
 Velocity = Displacement / Time taken
Speed ,Velocity and Acceleration

Speed is the quantity which shows how fast the body is
moving but velocity is the quantity which shows the
speed as well as the direction of the moving body.
Finally …….
Acceleration
Acceleration is the rate of change of velocity
(or) it is the change of velocity in unit time.
It is a vector quantity.
The SI unit of acceleration is ms-2
Acceleration = Change in Velocity
Time
a = (Final velocity – Initial velocity)
Time
a = (v–u)
t

Newton's Laws
Isaac Newton , a 17th century scientist, put forth a variety of
laws that explain why objects move or don't move .
His three laws are known as Newton's three laws of motion.
Newton’s First Law of Motion
 sometimes referred to as the law of inertia.
 Inertia - Inability to change the state of rest or of uniform
motion in a straight line.
 It depends on the mass of the object
 Newton's first law of motion states that, if a body is in the
state of rest or is moving with a constant speed in a
straight line, then the body will remain in the state of rest
or keep moving in the straight line, unless and until it is
acted upon by an external force.

Newton’s Second Law of Motion
The rate of change of momentum of a body is directly
proportional to the force applied on it, and the momentum
occurs in the direction of the net applied force.
F= ma [F =dp/dt]
Momentum
The momentum of a body is equivalent to the product of
its mass and velocity.
P = mv
Momentum – a moving force
Finally ….
 The state of motion or rest cannot be changed without
applying force.
 If a body is moving in a particular direction, it will keep
moving in that direction, until an external force is applied
to stop it.

Newton’s Third Law of Motion
 Third law of motion states that , to every action, there is
always an equal and opposite reaction.
 When two bodies interact with each other, they
exchange force, which is equal in magnitude but act in
opposite directions.
 This law has a huge application in static equilibrium
where the forces are balanced, and also for objects
which undergo uniform accelerated motion.

When a force acts upon an object to cause a displacement
of the object, it is said that work is done upon the object.
Requirements of work:
1. Force
2. Displacement
Work is only done when the force applied can change the
direction of the object or move it.
Work
Work can be expressed by the following equation
W = F • d • cos Ө
Unit is Nm or joule or J

Energy
 The capacity to do work is called energy [OR] energy is
the ability to work.
 It is in scalar quantity and has only magnitude and no
direction.
Law of Conservation of Energy
 Energy can neither be created nor destroyed, it can only
change in its form.
 The most important types of energy are kinetic energy
and potential energy.
Potential Energy – mgh
Kinetic Energy = ½ mv2
Unit of Energy is Nm or joule or J

Power
The time rate of work done by a body is called its power.
 Power = Rate of doing work = Work done / Time taken
Power p = W / t = F * s / t
But ,s / t = v is velocity . So P = F * v = F v cos θ
where θ is the smaller angle between F and v.
 Power is a scalar quantity.
 Its SI unit is watt. Its other units are kilowatt and
horsepower,
1 kilowatt = 1000 watt
1 horsepower = 746 watt

Force
 A push or pull acting on any
object is considered as a force.
 It makes things move or makes
them to change their state of motion.
Effects of Force:
 It can stop a moving object and vice versa.
 It can change the direction of a moving object.
 It can change the shape of an object

fundamentals of Force , Motion and Work.ppt

Magnitude of Force
The force is calculated using, F= ma
Where m – mass of the object in kg
a - acceleration of the object in ms-2
The unit of force is Newton.
1Newton is defined as the force that is required to
accelerate a mass of one kilogram at a rate of one meter per
second.
Resolution of Force
When a force is resolved into two parts along two mutually
perpendicular directions, without changing its effect on the
body, the parts along those directions are called resolved
parts. The process is called the resolution of a force.

Centripetal and Centrifugal Forces
Centripetal and centrifugal forces are
the forces experienced by rotating
objects.
The centripetal force keeps an object
moving in a circle and is always pointed
toward the center of that circle.
Examples
1. The sun’s gravity provides the centripetal force that
keeps the planets moving in their orbits
2. A rock tied to the end of a string, with the other end tied
to something or in your hand

Centrifugal force is an apparent outward force on an object
that is moving in a circle.
Examples
1. The bulging of earth at equator and flattering at the
pole is due to centrifugal force acting on it.
2. When a car in motion takes a sudden turn towards
left, passengers in a car experiences an outward
push to the right.
Comparison of centripetal and Centrifugal Force

Formulae:
Centripetal Force =
= mrꞶ2
Centrifugal Force = - Centripetal Force

In Physiotherapy…………
Motion
 Strengthen muscles and joints
 Increase flexibility
 Heal soft tissue and joint lesions
 Maintain existing joint and soft tissue mobility
 Displacement, velocity, and acceleration are crucial in the
assessment of a patient's walking or running patterns
(gait).
 Gait analysis uses to identify abnormalities, imbalances,
and potential issues in a patient's movements.
 By analyzing the displacement (distance covered), velocity
(speed of movement), and acceleration (changes in
velocity), physiotherapists can pinpoint areas where
improvements are needed and design targeted treatment
plans.
Displacement, Velocity, and Acceleration

Centripetal and Centrifugal force
Balance and Stability Training: Physiotherapists may use
exercises that involve circular or rotational movements to
improve a patient's balance and stability. These exercises
challenge the body to maintain equilibrium, which involves
muscle activation to produce centripetal forces to counteract the
outward forces generated by the movement.
Sports rehabilitation: Movements such as throwing, swinging,
or kicking can involve centripetal forces that physiotherapists
help patients relearn.
Therapeutic Exercise Equipment: Some physiotherapy
equipment, such as resistance bands or pulley systems, can
create outward forces on the limbs, which could be considered
analogous to centrifugal forces. These forces can be used to
provide resistance during exercises, helping to strengthen
specific muscle groups or improve joint stability.

fundamentals of Force , Motion and Work.ppt

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