Medical Physics PH
103
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other a little bit better !
 Encourage the co-operative learning,
 Built-up the research culture between the students,
 To study the basic principles of physics that are relevant to
the medical field.
 To apply the principles of physics in understanding various
body functions to develop health/medical disciplines.
The international systems of units
In earlier time scientists of different countries were using different
systems of units for measurement.
Three such systems, the CGS , the FPS (or British) system and the MKS
system are usually used. The base units for length, mass and time in
these systems as follows:



In CGS system they were centimetre, gram and second respectively.
In FPS system they were foot, pound and second respectively.
In MKS system they were metre, kilogram and second respectively.
What is the definition of the following terms:
Meter, Second and Kilogram
Metric Prefixes
 Physical objects or phenomena may vary widely.
 For example, the size of objects varies from something very small
( like an atom ) to something very large ( like a star ).
 The standard metric unit of length is the meter. So, the metric system
includes many prefixes that can be attached to a unit, each prefix is
based on the factors of 10 (10, 100, 1,000, etc., as well as 0.1, 0.01,
0.001, etc.).
 Conversion of Units
 Sometimes you must convert units from one measurement
system to another or convert within a system (for example,
from kilometers to meters). Equalities between SI and U.S.
customary units of length are as follows:
 Conversion of Units
 Conversion of Units
 How can you convert 15.0 in. to centimeters?
1 in = 2.54 cm
15 in = X cm
15 𝑥 2.54
∴𝑋=
= 38.1 cm
1
 How can you convert 200 mile to Km?
1 Mile = 1.609 Km
200 Mile = X Km
200 𝑥 1.609
∴𝑋=
= 321.8 𝐾𝑚
1
 Conversion of Units
 How can you convert 60 Kg. to g?
1 kg = 1000 g
60 Kg = X g
60 𝑥 1000
∴𝑋=
1
= 60000 g
 How can you convert 120 hours to sec?
1 hours = 3600 sec
120 hours = X sec
120 𝑥 3600
∴𝑋=
= 432000 𝑠𝑒𝑐
1
 Conversion of Units
 The distance between two cities is 100 mi. What is the
number of kilometers between the two cities? (a) smaller
than 100 (b) larger than 100 (c) equal to 100
1 mi = 1.609 Km
100 Mile = X Km
100 𝑥 1.609
∴𝑋=
1
= 160.9 𝐾𝑚
Introduction
 Physical Quantities
 A Physical quantity is a property of a material or system that can
be quantified by measurement. A physical quantity can be
expressed as the combination of a magnitude and a unit.

Physical quantities are classified into two types
1- Basic Quantities
2- Derived Quantities
Introduction
Basic (Fundamental) Quantities are quantities which are distinct in
nature and cannot be defined by other quantities. Basic quantities are
those quantities on the basis of which other quantities can be expressed.
Derived quantities are defined based on the other physical quantities.
Introduction
KINEMATICS
 Kinematics is that part of mechanics which is concerned
with the description of motion.
 Only six concepts are needed: time, distance, displacement,
speed, velocity and acceleration
Distance and Displacement
The distance :- is defined as the length of the path that the
object took in travelling from one place to another (scalar
quantity).
Displacement, on the other hand, is the distance travelled, but
with a direction associated
Speed and Velocity
In physics, we redefine these two words, speed and velocity,
so that they have similar, but distinct meaning.
The velocity:- is the change in its position, divided by the time
it took for this change to occur. Velocity is a vector and has
both a magnitude and a direction.
.
∆𝒙
𝒗=
∆𝑡
where v is the velocity vector, ∆x is the displacement vector
and ∆t is the time interval over which the displacement occurs.
∆𝒙 = 𝒙𝒇 − 𝒙𝒊
Speed and Velocity
Speed is the magnitude of the velocity. Speed is a scalar, and
it does not have a direction.
The speed of an object is the distance travelled, divided by the
time it took to travel that distance
∆𝑥
𝑣=
∆𝑡
Acceleration
The acceleration, a, is a vector which quantifies changes in
velocity.
In physics, acceleration is defined to be the rate of change (in
time) of the velocity:
a=
∆𝒗
∆𝑡
∆𝒗 = 𝒗𝒇 − 𝒗𝒊
𝒗𝒇 = 𝒗𝒊 + 𝒂𝒕
Acceleration is a vector, The acceleration is the rate of change
of the velocity, and velocity is a vector, therefore acceleration
must also be a vector.
Average Velocity or Speed
The average velocity is not require any knowledge of the
details of your trip.
𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑚𝑒𝑛𝑡 𝑑
𝑣𝑎𝑣𝑒𝑟𝑎𝑔𝑒 =
=
𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒
𝑡
𝒅 = 𝒗𝒂𝒗𝒆 ∙ 𝒕
𝟏
𝒅 = 𝒗𝒊 + 𝒗𝒇 𝒕
𝟏 𝟐
𝒅 = 𝒗𝒊 + 𝒗𝒊 + 𝒂𝒕 𝒕
𝟐
𝟏 𝟐
𝒅 = 𝒗𝒊 𝒕 + 𝒂𝒕
𝟐
Example 1:- If you drop a cricket ball from a 125 m high
tower, how far will it fall in 5 s?
since the initial velocity is zero
𝑣𝑖 = 0 (m/s)
𝑔 = 10 (𝑚/𝑠 2 )
𝟏 𝟐
𝒅 = 𝒗𝒊 𝒕 + 𝒂𝒕
𝟐
𝟏
𝒅 = 𝟎 + (𝟏𝟎 ∗ (𝟓 ∗ 𝟓)
𝟐
𝒅 = 𝟏𝟐𝟓 𝒎
Example 2:- If you throw a cricket ball straight up at 12 m s–1,
how high will it go?
since the initial velocity is 12
𝑣𝑖 = 12 (m/s)
since the final velocity is 0
𝑣𝑖 = 0 (m/s)
1
𝑣𝑎𝑣𝑒 = 𝑣𝑖 + 𝑣𝑓
2
𝑚
𝑣𝑎𝑣𝑒 = 6
𝑠
𝑣𝑓 − 𝑣𝑖
∆𝑣
0 − 12
−12
𝑡=
=
=
=
= 1.2 𝑠
𝑔
𝑔
−10
−10
𝑑 = 𝑣𝑎𝑣𝑒 ∗ 𝑡 = 6 ∗ 1.2 = 7.2 𝑚
Dimensional Analysis
 The word dimension has a special meaning in physics. It denotes the
physical nature of a quantity .
 Whether a distance is measured in units of feet or meters , it is still a
distance. We say its dimension is length.
 The Dimensional Analysis makes the use of the fact that dimensions
can be treated as algebraic quantities.
 dimensional analysis is the analysis of the relationships between
different physical quantities by identifying their base quantities
 Dimensions can be treated as algebraic quantities . What dose it
mean?
Quantities can be added or subtracted, only if they have the same
dimension.
 The terms on both sides of an equation must have the same
dimensions
By following these simple rules, you can use dimensional analysis to
determine whether an expression has the correct form. Any relationship
can be correct only if the dimensions on both sides of the equation are the
same.
 Find the dimension equation for the Velocity, Acceleration,
Force, Density, Volume, Pressure.
 1- Velocity
𝐿𝑒𝑛𝑔𝑡ℎ
𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =
𝑇𝑖𝑚𝑒
𝐿
𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =
𝑇
The dimension equation for the Velocity is 𝐿𝑇 −1
 2- Acceleration
𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦
𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑇𝑖𝑚𝑒
𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =
𝐿𝑒𝑛𝑔𝑡ℎ
𝑇𝑖𝑚𝑒
∴ 𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 =
𝐿𝑒𝑛𝑔𝑡ℎ
𝑇𝑖𝑚𝑒 𝑥 𝑡𝑖𝑚𝑒
=
𝐿𝑒𝑛𝑔𝑡ℎ
𝑇𝑖𝑚𝑒 2
𝐿
𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 = 2
𝑇
The dimension equation for the Acceleration is 𝐿𝑇 −2
 3- Force
𝐹𝑜𝑟𝑐𝑒 = 𝑀𝑎𝑠𝑠 𝑥 𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑟𝑎𝑖𝑜𝑛
𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦
𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑇𝑖𝑚𝑒
𝐿𝑒𝑛𝑔𝑡ℎ
𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =
𝑇𝑖𝑚𝑒
𝐿𝑒𝑛𝑔𝑡ℎ
𝐿𝑒𝑛𝑔𝑡ℎ
∴ 𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 =
=
𝑇𝑖𝑚𝑒 𝑥 𝑡𝑖𝑚𝑒
𝑇𝑖𝑚𝑒
𝐿
𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 = 𝑇 2
𝐿
𝐹𝑜𝑟𝑐𝑒 = 𝑀 𝑥 𝑇 2
The dimension equation for the Force is M 𝐿𝑇 −2
2
 3- Volume
𝑉𝑜𝑙𝑢𝑚𝑒 = 𝐿𝑒𝑛𝑔𝑡ℎ 𝑥 𝑤𝑖𝑑𝑡ℎ 𝑥 ℎ𝑒𝑖𝑔ℎ𝑡
𝑉𝑜𝑙𝑢𝑚𝑒 = 𝐿𝑒𝑛𝑔𝑡ℎ 𝑥𝐿𝑒𝑛𝑔𝑡ℎ 𝑥 𝐿𝑒𝑛𝑔𝑡ℎ𝑡
The dimension equation for the Volume is 𝐿 3
 4- Density
𝑀𝑎𝑠𝑠
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 =
𝑚3
𝑉𝑜𝑙𝑢𝑚𝑒
𝑉𝑜𝑙𝑢𝑚𝑒 = 𝐿𝑒𝑛𝑔𝑡ℎ 𝑥 𝑤𝑖𝑑𝑡ℎ 𝑥 ℎ𝑒𝑖𝑔ℎ𝑡
𝑉𝑜𝑙𝑢𝑚𝑒 = 𝐿𝑒𝑛𝑔𝑡ℎ 𝑥𝐿𝑒𝑛𝑔𝑡ℎ 𝑥 𝐿𝑒𝑛𝑔𝑡ℎ𝑡
The dimension equation for the Volume is 𝑀𝐿 −3
 5- Pressure
𝐹𝑜𝑟𝑐𝑒
𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 =
𝐴𝑟𝑒𝑎
∴ 𝐴𝑟𝑒𝑎 = 𝐿𝑒𝑛𝑔𝑡ℎ 𝑥 𝑙𝑒𝑛𝑔𝑡ℎ
𝐴𝑟𝑒𝑎 = 𝐿 2
𝐿
𝑇
𝑀
𝐿
The dimension equation for the Pressure is M 𝐿 −1 𝑇 −2 Kg 𝑚 −2
 Show that the following equation is dimensionally
correct:
 Quizzes
Q uick .Q uiz 1 : Define the fundamental quantities?
Q.Q2 : Write 5 derived quantities.
Q.Q3: Why time is basic quantity and Velocity is derived quantity?
Q.Q4 : Determine which of the following is scalar and which is
vector quantities?
Distance – Displacement – Speed- Mass – Velocity- AccelerationWeight- Time - Force - Energy – Momentum - Pressure
 Quizzes
Q.Q6 : True or False, and kindly explain why:
•
Dimensional analysis can give the numerical value of constants.
• The dimension equation for acceleration is 𝐿 t − 2
•
The dimension equation for volume is L
• All quantities has dimension equation
•
Dimensions can be treated as algebraic quantities
•
Dimensions can be used for checking the correctness of the form of
the equation
 Quizzes
Q.Q7 :
Please find the dimension equation for the following
terms: Force, Pressure, and Density
Q.Q 8 Show that the following equation is dimensionally
correct:
𝑉 = 𝑎𝑡
where ( 𝑉 𝑜 ) is velocity and ( 𝑎 ) is acceleration
 Quizzes : Serway – Physics for Scientists _Page 14
 Quizzes : Serway – Physics for Scientists _Page 15