kinetics in biomechanics

1. KINETICS.
- Dr Mansi kotecha (BPT).

2. CONTENTS.
1. Force
2. Calculating force
3. Types of forces
4. Force vector
5. Naming forces
6. Force of gravity
7. Equilibrium
8. Force system

3. FORCE.
• Definition
force is that which producers the motion or modifies the motion of an
object and moves it for a particular distance.
• In simple terms it is push or pull exerted by an object or substance on
another
• for example pushing a wheelchair
• force is an vector quantity
• Unit:- Newton (N)

4. FORCE
• 1 Newton
it is the amount of force required to push or pull an object of 1 kg to 1
metre distance
• here
force can act on two varieties of object
1. static
2. dynamic

5. CALCULATING FORCE
• Force (F) = mass (m) × acceleration (a)
• Where
mass is in kg
acceleration is metre per second square
• kg×m/sec2

6. TYPES OF FORCES
THERE ARE TWO TYPES OF FORCE
• external force :- push or pull on an
body that arise from a source which is
outside of a body
• for example gravity
• Internal force are the forces that act
on a structure of body and also arise
from bodies on structure
• example muscle pull

7. • Note
external force either facility or restrict moment
• Where as
internal force mostly initiate the movement
• however
internal force also control or counteract movement produced by external
force.

8. FORCE VECTOR
• Force vector is representation of force that has both magnitude and
direction
• Vector is represented by an arrow
• here
• tail is point of source a force
• Shaft indicates magnitude
• Arrowhead indicates direction

10. NAMING FORCE
• Something on something
• First part of force indicates source
of force
• Second part of force indicates object
or subject on which it is being acted on.

11. FORCE OF GRAVITY
• Force of gravity acting on object or segment is considered to have its
point of application at the centre of mass or centre of gravity (COG).
• So
• COG is an imaginary point at which mass of an object is concentrated
• in an symmetrical object COG is present at the centre of body
• In an asymmetrical object COG is present at the heavier end where mass
is concentrated

13. COG IN HUMAN BODY
• Centre of mass of human body lies approximately anterior to the second
sacral vertebra ( S2)
• so
• centre of gravity lies in 2nd sacral vertebrae in human body
• in human body each and every segment of the body has its separate
COG and two or three segment together gives different COG
• for example the arm forum and hand will be having its own separate
but the upper link as a whole give some different or other COG

14. LINE OF GRAVITY (LOG)
• Line of gravity is imaginary vertical line passing
through the centre of gravity

15. STABILITY / BASE OF SUPPORT (BOS)
• The base of support means the area supported beneath the object.
• Whenever the base of support is more the stability will be more
• Greater base of support lower the COG of any object
• For example the fundamental position of standing the base of support
is lesser than the lLaying so COG in standing position is higher in levels
• where is in laying position it will be changed near to the ground as a
result lying posture is more stable than any other fundamental position
and also it can be maintained for longer period

17. INTERRELATION OF CENTRE OF
GRAVITY, LINE OF GRAVITY & STABILITY
• The stability is directly proportional to base of support and inversely
proportional to centre of gravity
• For an object to be stable the line of gravity must fall within base of
support
• When the line of gravity is outside the base of support the object will be
unstable

19. EQUILIBRIUM
• Equilibrium is act of balancing all keeping in remain rest of the body
even though the force is exerted on it
• Or in other words it is the state of an object where all the force acting
on it are equal in magnitude and opposite in direction

20. TYPES OF EQUILIBRIUM
• It is classified into following three types
1. Stable equilibrium
2. Unstable equilibrium
3. Neutral equilibrium

21. STABLE EQUILIBRIUM
• The object will restored in resting position even though the force alters
its equilibrium this is called As stable equilibrium
• Generally The equilibrium will be more when the base of support is
more and lies in lower part of the object
• for example book placed on the table when the force is applied on the
book to book regains its original state after the removal of the force

22. UNSTABLE EQUILIBRIUM
• The minimum force is enough to alter the equilibrium of an object is
called as unstable equilibrium
• The base of support is less and CUG is in the higher position
• for example pen is balanced on stand on the floor when the force is
applied to the pen it alters its original State

23. NEUTRAL EQUILIBRIUM
• even though the movement or position changes in the object by the
force exerted on it there will be no change in the centre of gravity of
the object
• For example Ball is rolling on the floor

25. FORCE SYSTEM
• There are four types of force system
1. Linear force system
2. Parallel force system
3. Rotational force system
4. Concurrent force system

26. LINEAR FORCE SYSTEM
• If the two force are acting along the same line and produces the straight
line motion is referred as linear force system
• Example
1. when two forces are acting on an object in same direction produces the
linear motion the force has take to be pushing linear force.
2. When the two force pull an object in same direction it produces the linear
motion and the force is is said to be e pulling linear force
3. When the two forces are acting opposite to each other with equal
magnitude results in in equilibrium
4. when the two forces are acting opposite to each other with an equal
magnitude the moment occurs towards the greater magnitude side

28. PARALLEL FORCE SYSTEM
• The two equal magnitude are acting in same direction and same plane
with counter force in the middle
• Example see-saw
• The children are applying the force in the end of and the Fulcrum give
the counter force to maintain the see-saw in neutral position

29. ROTATIONAL FORCE
• In the parallel forces any one of the force is greater than other results
to the rotation of the object and the force is known as rotational force
• In other words if two different magnitude force act on different point
of the object result in rotation of the rotation movement
• that is twisting effect the forces are said to be force couple

30. CONCURRENT FORCE
• if the two forces are acting on an object in different direction is
perpendicular to each other the resultant force will be in between the
two forces it can be diagrammatically represented by a parallelogram
method

31. REFERENCE..
• Textbook of therapeutic exercise – lakshmi narayana
• Joint structure and function – Cynthia norkins