2. Force : The Cause of Motion
Every acceleration is caused by
forces acting on a body
Force is a push or a pull
15 N
The strength of a force determines
the magnitude of the acceleration
Arrows are used to represent
5N
forces. The length of the arrow is
proportional to the magnitude of
the force.
3. Newton’s Laws of Motion
First Law
What happens in the absence of force
Second Law
The effects of applying a force to an object
Third Law
Forces are caused by interactions of two objects
4. First Law of Motion: Inertia
An object continues in a state of rest
or in a state of motion at a constant
speed along a straight line, unless
compelled to change that state by a
net force (unless acted on by an
external unbalanced force).
The net force is the vector sum of all
of the forces acting on an object.
r
∑
The SI unit of force is the Newton (N).
F
5. First Law of Motion: Inertia
Unbalanced force: difference between
downward and upward forces
Balanced force: net force is zero.
Terminal velocity is constant.
6. First Law of Motion: Inertia
Inertia: is the natural tendency of an
object to remain at rest in motion at a
constant speed along a straight line;
“Resists changes in motion”
8. Newton’s Second Law
When a net force acts on an object, the object r
accelerates in the same direction as that force.
r
a=
∑ F
The acceleration is directly proportional to the net m
force and inversely proportional to the mass of the
object.
The bigger the force, the greater the acceleration;
the larger the mass, the smaller the acceleration. r r
∑ F = ma
Force = mass (kg) x acceleration (m/sec2)
1 newton = 1.0 kg-m/sec2
11. Newton’s Second Law of Motion
A free-body-diagram is a diagram that represents the
object and the forces that act on it.
The net force in this case is: 275 N + 395 N – 560 N = +110 N
and is directed along the + x axis of the coordinate system.
12. Newton’s Second Law of Motion
If the mass of the car is 1850 kg then, by
Newton’s second law, the acceleration is
a=
∑ F = + 110 N = +0.059 m s 2
m 1850 kg
13. Problem
A 440-g can of food is given a shove on a
frictionless level surface and is observed to
accelerate at a rate of 1.5 m/sec2. What is
the force of the shove?
r r
∑ F = ma
0.66 N
14. Third Law : Action – Reaction
For every action, there is an
equal and opposite reaction.
Whenever one body exerts a
force on a second body, the
second body exerts a force
back on the first that is equal in
magnitude and opposite in
direction.
Fa = - Fb
17. FORCES
a push or pull
a vector quantity
any influence that is capable of
producing a change in the state of
motion
The magnitude is determined by its
strength
Unit = m x a ; 1kg m/s; 1 Newton (N)
18. Two General Types of Forces
Fundamental
Gravitational Force
Strong Nuclear Force
Electroweak Force
Non-fundamental
Friction
Tension in a rope
Normal or support forces
19. Gravity Attractive force that acts between any
two objects in the universe.
Gravitational attraction of the earth endows objects with
weight and causes them to fall to the ground when dropped.
20. Newton’s Law of Universal Gravitation
Between any two objects in the universe there is an
attractive force (gravity) that is proportional to the
masses of the objects and inversely proportional to
the square of the distance between them.
F = G x m1 x m2
d2
Gravitational constant = 6.673 x 10-11 N-m2/kg2
21. The Gravitational Force
What is the magnitude of
the gravitational force
that acts on each particle,
assuming
m1= 12kg, m2 = 25kg
and r = 1.2m?
m1m2
F =G 2
r
(
= 6.67 ×10 −11
N ⋅ m kg
2 2
) (12 kg )(25 kg )
(1.2 m )2
= 1.4 ×10 −8 N
22. The acceleration due to gravity
g = G x ME
RE2
ME
g =G 2
RE
( −11
= 6.67×10 N⋅ m 2
kg )
2 (5.98×10 kg)
24
(6.38×10 m)
6 2
= 9.80m s 2
23. Weight and Mass
Force between two objects in the
earth : gravitational attraction
Weight: force of gravity on an object
Unit is Newton
Mass: amount of matter in the body
Unit is kg
Weight depends on where you are.
Where would you weigh less, sea
level or mountain top?
24. The Gravitational Force
Relation Between Mass and Weight
M Em
W =G 2
r
ME
W = mg g =G 2
r
A cantaloupe has a mass of 0.5
kg. What does it weigh?
4.9 newtons
25. Apparent Weight
The apparent
weight of an
object is the
reading of the
scale.
It is equal to the
normal force the
man exerts on the
scale.
26. Gravity and Varicose Veins
Like all things on earth, circulating
blood is subject to gravity.
When in a standing position,
“blood is redistributed to regions
below the heart and venous return
is reduced” (Gisolf, 2004).
Many complications arise from
abnormal blood vessel flow, one
of which --- is recognized as the
bane of middle-age life in women:
varicose veins.
27. Gravity and Varicose Veins
The cause of varicose veins is very
much related to the gravitational
influence on blood flow.
In a standing position, blood pools in
the peripheries.
If the valves become weak, blood can
leak back into the vein and collect
there. This is called venous
insufficiency.
In order to test for the extent of the
valve’s weakness one can perform a
Doppler test or a Trendelenburg
test.
28. Gravity and Varicose Veins
FACTORS TREATMENT
Increasing Age Support
Genes Leg elevation
Hormonal changes. Injection sclerotherapy is a
Pregnancy surgical treatment in which the
Obesity, leg injury, prolonged veins are injected with a
standing and other things that chemical that closes them
weaken vein valves completely.
Sun exposure, which can cause Ligation and stripping (which
spider veins on the cheeks or means tying and pulling out) is a
nose of a fair-skinned person technique used to remove the
surface veins either partly or
SYMPTOMS of varicose veins can altogether.
range from the mild aching, itching
and swelling of the legs and ankles
29. Gravity and Varicose Veins
PREVENTION
avoid standing still for long
periods of time
take regular exercise, such
as walking
maintain a healthy weight
wear properly fitted
compression stockings to
prevent further
deterioration of existing
varicose veins.
30. Gravity Drainage
Gravity drainage simply
means the removal of
either air, water or solid
from the body through the
use of gravity and negative
pressure.
This process is due to
gravity because as the catheter
bag is placed in a level lower
Examples of this are than the level of the bladder, and
catheters, nasogastric air and fluid is caused to move from
tube, chest tube drainage an area of higher level to a low
level. It also creates a negative
and postural drainage. pressure in the bag that forces the
urine out.
31. Gravity Drainage
It is mainly used to relieve
The chest tube drainage system is composed of
gastric pressure by draining
the chest tubes and an outlet. The outlet maybe:
air, liquid and solids in the one bottle water system, two bottle or the short
stomach term catheterization and lastly using the three
bottle or water pleural drainage system.
Fluid flowing back into the patient may be a
source of infection, in addition to reducing
capacity for gas exchange.
32. Gravity Drainage
Postural drainage aims to
remove secretions by gravity
In this procedure, the patient is
twisted and turned so as to
facilitate the movement of the
hands.
The patient is positioned with
the area of the lung with
retained secretions higher than
the airway though which those
secretions will drain
Postural drainage therapy is often
used in conjunction with aerosol
administration and other
respiratory care procedures.
33. The Normal Force
Definition of the Normal Force
The normal force is one component
of the force that a surface exerts on
an object with which it is in contact
– namely, the component that is
perpendicular to the surface.
34. The Normal Force
FN − 11 N − 15 N = 0
FN = 26 N
FN + 11 N − 15 N = 0
FN = 4 N
35. Centripetal Force
Ac = v2/r
Fc = mv2/r
An object stays in a
circular path as long as
this force acts. If this
disappears, the object
moves in a straight line
Central-seeking force
36. Force of Friction
It is the force generated by the
properties of the interface
between the object and the
surface
Ff = µN
N = Normal force – force
perpendicular to the surface
µ = coefficient of friction
37. Static and Kinetic Frictional Forces
When an object is in contact
with a surface there is a force
acting on that object. The
component of this force that is
parallel to the surface is called
the frictional force.
Note that the magnitude of the
frictional force does not depend
on the contact area of the
surfaces.
38. Types of Force of Friction
Depends on the physical state of motion
Static force of friction: If at rest / stationary
Ff,s = µsN ;
net F > Ff,s = object set to motion
Kinetic force of friction: if in motion
- Ff,k = µ kN ; keeps it in motion
39. Static and Kinetic Frictional Forces
When the two surfaces are
not sliding across one another
the friction is called
static friction.
The magnitude of the static frictional
force can have any value from zero
up to a maximum value.
0 < µs < 1
is called the coefficient of static
friction.
40. Static and Kinetic Frictional Forces
Static friction opposes the
impending relative motion between
f k = µ k FN
two objects.
Kinetic friction opposes the relative 0 < µs < 1
sliding motion motions that actually is called the coefficient of kinetic friction.
does occur.
41. Friction and Osteoarthritis
Osteoarthritis –
Inflammation of joints
Joints – Synovial
membrane
Synovial fluid
Almost same consistency
of water
µ - 0.005 to 0.02
Force of friction Ff = µ W
W = mg
42. The Tension Force
Tensions - forces exerted by
strings or ropes, cables
Cables and ropes transmit
forces through tension.
A “massless” rope will transmit tension
undiminished from one end to the other.
If the rope passes around a massless,
frictionless pulley, the tension will be
transmitted to the other end of the rope
undiminished.
43. Traction Systems
• A traction apparatus exerts a force on one of
the patient’s extremities net force.
• a combination of pulleys with a weight to
exert force
Traction System
Rope/cord – transmits tension
Pulleys – shifts direction of tension
Force = Weight = Tension applied
45. Purposes of Traction
Treatment of fractured extremities
To lessen muscle spasm
To reduce fracture
To provide immobilization
To maintain proper alignment of bones
To prevent and correct deformity
For support
49. Relationship of MUSCLES to
FORCE and TENSION
Muscles are attached -
tendons – bones
Tendons – rope-like
function;
Tension- tendency of a
rope to be pulled apart
due to forces applied at
each end
Force –shortening of
muscles
Pulling effect
> contractions - > tension
> pulling effect > force
Contractions – shortens
distance between points of
attachments
