Physical concept

2. Basic Concept in Biomechanics
2
Ch.1 : Basic Concept in Physics
File no. 1

3. Content Layout
1. Introduction (SI Units , prefixes, physics quantities types)
2. Translation Motion of objects
3. Force and Newton`s Law of motion
4. Work, energy, power
5. Rotational motion of objects, torques and lever system
6. Pressure and Hydrostatic pressure
3

25. Jehad Ahmed ALSHANTY 25
Q.3: Federal guidelines suggest that the maximum safe sideways acceleration in a
turn is 1 𝒎 𝒔𝟐
. What is the minimum radius curve a civil engineer should design
on a road where cars travel at 30 m/s ?

36.  Inertia: the resistance an object has to a change in
its state of motion.
 Mass: is a fundamental property of the object; a
numerical measure of the amount of matter in the
object. It is a quantitative measure of inertia
 Weight : is the force of gravity on an object.
• Inertia
• Mass
• Weight
Jehad Ahmed ALSHANTY 36
Inertia/mass/weight

37. Jehad Ahmed ALSHANTY
37
Mass
Does not
depend on
gravity
Always
remains
constant
vs. Weight
Depends on
gravity
W=m x g
weight of an
object changes
if the gravity
changes
Mass vs Weight

38. Jehad Ahmed ALSHANTY 38
H.W.2:A bacterium, using its flagellum as propulsion, can move through liquids
at a rate of 0.003 m/s. Its mass is 𝟏 × 𝟏𝟎−𝟏𝟐
g. The viscous drag on a swimming
bacterium is so great, that if it stops beating its flagellum it will stop within a
distance of 0.01 nm.
a) What is the acceleration that stops the bacterium?
b) What is average magnitude of this viscous force?
c) What amount of force must the flagellum generate to push the bacterium at a
constant velocity of 0.003 m/s
d) If the bacterium wished to accelerate at a rate of 0.001 𝒎/𝒔𝟐 how much additional
force would be necessary?

43. 3

44. • Work
• Energy
• Power

45. 45
Work and Conservation of Energy
1. Conservative force : A force is conservative
when the work it does on a moving object is
independent of the path between the object's
initial and final positions.
Examples:
Electrical force, gravitational force, elastic force
2. Non-conservative force : A force is
nonconservative when the work it does on a
moving object is dependent of the path
between the object's initial and final positions
Examples:
Friction, Applied Force, Tension Force

48. 48
Energy Conversion in Humans
• Our own bodies, like all living organisms, are energy conversion machines.
• Conservation of energy implies that the chemical energy stored in food is converted into
work, thermal energy, and/or stored as chemical energy in fatty tissue.
• The fraction going into each form depends both on how much we eat and on our level of
physical activity. If we eat more than is needed to do work and stay warm, the remainder
goes into body fat

56. 4

59. 59

62. What the type of each lever class according to its mechanical
advantage?

63. 5

64. 6

65. 4

67. • Pressure is an expression describe the magnitude
of the force applied perpendicular to a unit area
of the surface of an object over which that force is
distributed.
• It is a scalar quantity.
• It represented by the symbol P .
• Its SI unit is Pascal
• There is a non-SI units for pressure like
67
Pressure
𝟏 𝑷𝒂𝒔𝒄𝒂𝒍 =
𝑵
𝒎𝟐

68. Jehad Ahmed ALSHANTY 68
Force/Pressure/Area
The greater the area
affected by the force the
lower the pressure

69. Jehad Ahmed ALSHANTY 69
Pressure and State of Matter
• A solid exerts pressure only in the
downward direction due its weight
• Liquids and gases exert pressure in all
directions. Because its molecules move
randomly and exert an equal force on
every surface in contact with them.

70. • The pressure exerted by a non-moving (static) fluid
at a given point within the fluid, due to the force of
gravity is called the hydrostatic pressure.
• The fluid pressure does not depend upon the shape
of the container or the amount of liquid in the
vessel. It depends on the depth and its density.
Jehad Ahmed ALSHANTY 70
Fluid Pressure
Video

71. • In the same fluid container, pressure
increase as the fluid height increase.
• Fluid exert equal pressure in all
direction in the same depth.
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Fluid Pressure
• Static Fluid pressure given by the formula :
m : mass
V: Volume
g : 10 m/s2
𝝆: 𝒅𝒆𝒏𝒔𝒊𝒕𝒚 (
𝒌𝒈
𝒎𝟑
)
Wearing compression
socks places pressure on the
veins in the lower legs. This
pressure can help improve
blood flow and prevent further
spider or varicose veins

72. Jehad Ahmed ALSHANTY 72
Absolute Pressure
= total pressure
Gauge pressure
𝑷𝒂𝒕𝒎=
𝑷𝒂𝒃𝒔=
𝒉 =
𝒎
𝒔𝟐
≈ 𝟏𝟎
𝒎
𝒔𝟐
Atmospheric pressure

73. 1
73
mercury
Q8
Jehad Ahmed ALSHANTY
Q 7

74. Jehad Ahmed ALSHANTY 74
H.W. 4: If the force on the eardrum increases by about 1.5 N above the
force from atmospheric pressure, the membrane can be damaged. If you go
for diving in the ocean, below what depth could damage to your eardrum
start to occur? The eardrum is typically 8.2 mm in diameter and sea water
density is 1030 𝒌𝒈 𝒎𝟑
Hydrostatic
pressure
5

75. Sec.1.2:
Review of Electricity
Ch.1: Basic Concept in Physics
75

76. What is Electricity ?
• Matter is made of very small particles called atom
• Atom has a nucleus, which consist of protons and
neutrons, and electrons located outside nucleus.
• When electrons move from one atom to another
atom, it produce electricity.
• Electricity: is the energy caused by moving
electrons from one place to another.
Jehad Ahmed ALSHANTY

77. Electrical Charge
• Electric charge is one of the property of matter that determine how the matter
interact with each other. This interaction is done by mean of electrical forces.
• Charge can be positive or negative, if there are excess of electrons in a particle they
are said to be negatively charged. And if a particle has less number of electrons, they
are called positively charged particles.
• Charge is a conserved quantity, it cannot be destroyed or created
• Its SI unit is Coulombs (C).
• It represented by the symbol Q.
• The charge of an electron is -1.6×10−19 C
Jehad Ahmed ALSHANTY

78. Electrical Force
• Charges exert forces on each
other, based on the law of electric
charges it could be attractive or
repulsive forces.
• The Electric force F between two charged bodies is proportional to the product of
their charges Q1 and Q2 and is inversely proportional to the square of the distance R
between them. This law is called Coulomb's Low , given as
+1 -1
Jehad Ahmed ALSHANTY

79. • The electric field magnitude that is set by a charged
particle is inversely proportional to the distance from
the particle.
• Force field E at any point is defined in terms of
the electrostatic force F that would be exerted on a
positive test charge q0 placed there.
79
Electrical Field
• The electric field is radially outward from a positive charge
and radially in toward a negative point charge.

80. Electrical Potential Difference
• The electric potential difference, also known as voltage, is the external work done to
push a unit positive charge from a reference point to a specific point against an electric
field.
• If the particle moves against the electric field it gains some amount of energy which is
defined as the electric potential energy:
Energy =∆VQ
𝑽𝒐𝒍𝒕 =
𝑱𝒐𝒖𝒍𝒆
𝑪𝒐𝒖𝒍𝒐𝒎𝒃

81. • The capacitor is an electrical component that stores electric charges in electronic circuits
• Its consist of two conducting materials, separated by a gap containing a non-conducting
material like air.
• If the capacitor is fully filled and in the absence of any source power in the circuit, it can
work as a battery
• Capacitance of a capacitor is constant and
measured in Farads (F).
81
Capacitor
It’s the
constant
∆𝑽
𝑬 =
𝟏
𝟐
𝑪 𝑽𝟐

82. DC Shock Defibrillator
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• In this method a capacitor is charged to a high DC voltage and then rapidly discharged.
• The amount of energy discharged by the capacitor may range between 2-400 Joule with
peak value of current 20 A
Extra
• A corrective shock of 750-800 volts is applied within a tenth of a
second to convert an abnormal heart rhythm to a normal heart
rhythm as in the case of atrial fibrillation.

83. Current
• The movement of charges due to potential difference establish an electric current.
• It could be a DC or AC type.
• It represented by the symbol I and given by:
Its SI-unit is amperes (A) = (C/s)
Where Q is the amount of charge travel through a conductor
with a given cross-section area in a given time
Jehad Ahmed ALSHANTY

84. Resistance
• Electrons can flow through any material, but does so more easily in some material than in
others. How hardly it flows is called resistance.
• Matter can be broken down into:
V = R I
1. Conductors: electrons flow easily Low resistance.
2. Semi-conductors: Variable resistance according to
formulation and circuit conditions.
3. Insulator: electrons flow with great difficulty High
resistance.
• The resistance of a material (R) is measured in Ohms (Ω)
• A resistor is the electrical component that implements electrical
resistance in electronic circuits. It used to reduce current flow.
• Ohm’s law :
It’s the
constant
Jehad Ahmed ALSHANTY

85. 85
Electricity and Magnetism
• An Electric Field surrounds any electric charge.
• Moving electric charge creates Magnetic Field 𝑩 in its surrounding area.
• A magnetic field exists in the region around a magnet.
• The unit of B (in SI unit) is Tesla.
 While the magnetic field lines
produced by a current flow on
a long straight wire form
concrete circles around the
wire, where the magnetic field
always at a direction
perpendicular to the current
flow.
 The magnetic field is a vector quantity.
 Outside the magnet, it points from the north pole to the south pole.

86. 86
Induced Current
• The current that is produced in the wire in this case is called the induced current and its
flows in the direction so that to oppose‫يعاكس‬ the change in the flux. It creates an induced
magnetic filed also.
• When a magnet is moved near a conducting wire, current flows through that wire without
any batteries! As this motion change the magnetic field through the wire area and hence the
magnetic flux changing.

87. 87
Flux of Magnetic Field
• Magnetic flux is the amount of magnetic field that passes through a loop
• Magnetic flux is a scalar. The unit of magnetic flux (in SI) unit is the weber (1Wb=1 T.𝑚2)