1. Momentum, Gravity & Equilibrium

2. Resolution of forces
Any vector that is directed at an angle can be considered to have two parts
Horizontal part
Vertical part

3. Here the single force can be resolved in to two components Vertical component shows the force on the dog upwards Horizontal component shows the force on the dog rightwards

5. Calculate the vertical and horizontal vector components in the following examples
Which component will make this cart move, horizontal or vertical ?

6. Calculate the resultant force
A single force that can be applied instead of several forces

7. Momentum
A quantity expressing the motion of a body or system, equal to the product of the mass of a body and its velocity
Vector quantity
Divided as Linear momentum & Angular momentum

8. Linear Momentum P = m v P = Momentum Momentum is frame dependant
M = Mass
V = Velocity
Momentum is frame dependant
in this ex. A is the reference compared to
that the apple has a V1 velocity
What can you say about the
next picture ?

9. Angular Momentum Object fixed to a relative fixed point
L= IW L = Angular momentum
I = Inertia
W = Angular velocity
Describe as the rotational analog of the linear momentum

10. Physiotherapy Applications

11. Action and reaction
To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts

12. State the place of reaction acting in the following action forces

13. Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other.
Types of Friction
Fluid friction
Lubricated friction
Skin friction

14. Reducing Friction Devices
Wheels, ball bearings, roller bearings, many thermoplastic materials ( nylon )
Physiotherapy application
Quadriplegic patients immobile for long period of time very porn for pressure sores. We apply water filled bad between the contacting surface and the bed.

15. Physiotherapy applications
Lubricants
Oil, water, grease
Physiotherapy applications
Mainly reduces the skin friction
In manipulative techniques as effleurage, stroking to reduce the skin friction we use talc/powder
When ultra sound treatments are given to provide a medium we use gel
When giving nerve stimulation to minimize the skin resistance we wet the electrode pads with water

16. Rotation and pivot
Three dimensional objects rotates either around an imaginary axis (rotational axis) or
around a point (pivot point)
Speed of the rotation is given by angular velocity

17. What is angular velocity?
Vector quantity
Velocity depends on the torque acting on the system
AV = Degrees/time
Units given by radius per second

18. Angular velocity Linear velocity
Vector Rotation around a fixed axis Velocity depends on the torque Velocity of a system or a group of objects V= r w
Vector Not around a fixed axis Depends on external forces Velocity of a single object

19. Angle of pull of a muscle
The angle between the line of pull and the portion of mechanical axis between the point of application and the joint

20. Force may be resolved into a vertical and a horizontal component
Size of each depends on angle of pull
A muscle’s angle of pull changes with every degree of joint motion
So do the horizontal & vertical components
The larger the angle ( ), the greater the vertical and less the horizontal components

21. Most resting muscles have an angle of pull < 900
Angle of pull ctd
Vertical component is perpendicular to the lever, and is called the rotary component (aka angular force or movement force)
Horizontal component is parallel to the lever, and is called the nonrotary component (aka stabilizing force)
Most resting muscles have an angle of pull < 900

22. Rotary vs Nonrotary components
Angle of pull < 900
As the angle of pull gets smaller, the moment arm decreases.
Nonrotary force is directed toward fulcrum
Stabilizing effect
Helps maintain integrity of the joint
Almost all of the force generated is
directed back to the joint, pulling the
bones together

23. Angle of pull > 900 Nonrotary force is directed away fulcrum
Dislocating component
It is called a dislocating force because the force generated is directed away from the joint
Muscle is at limit of shortening range
and does not exert much force

24. Angle of pull = 900
Force is all rotary/angular force
The moment arm is at its greatest length
Angle of pull = 450
Rotary & nonrotary components are equal
Muscular force functions:
Movement
Stabilization

25. Gravity
Natural phenomenon by which physical bodies attract with a force proportional to their mass
Earth is surrounded by its own gravitational force
The strength of the gravitational field is numerically equal to the acceleration of objects under its influence
value at the Earth's surface 9.81 m/s2

26. W = mg When an object is falling under the influence of gravity
Its acceleration equals to the gravitational field
Weight of an object on the earth is taken as,
W = mg
W = weight
m = mass of the object
g = gravitational field

27. Center of Gravity (COG)
Balance point, weight on all sides equal
Average location of the weight of an object
How do you determine the COG in a equal shape object?
How do you determine the COG in irregular shape object ?

29. Line of Gravity Vertical line that passes through COG
Represents the direction gravity acts on the body

30. Equilibrium State of Equilibrium
All forces acting on an object are balanced
Base of Support (BOS)
Part of body/object in contact with supporting surface
Has different shapes, according to the contact surface
More the base of support increases more the stability of an object

31. What can you say about the shapes of following BOS

32. BOS in physiotherapy
Patients need a support to increase there functional independence.
Patients with fractures
Elderly patients
Muscular imbalances

33. Aids use in physiotherapy to increase BOS and support

34. States of Equilibrium Stable Unstable Neutral
COG must be raised in order to disturb object
Unstable
Only slight force needed to disturb
Neutral
Object disturbed but no change in COG (ball)