Chapter 2and 3 Final

8/2/2019 Chapter 2and 3 Final

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DEFINITION

Kinematics:

Systematic study of motion using distance, speed, time and acceleration is called

kinematics

Distance:

It is the length of path (scalar quantity)

Speed:

It Is the time rate of change of distance

Displacement:

It is the change in position of a particle from initial position to final position

Position:

It is the location of a particle with respect to reference point (origin)

X1

X2

X1

X1


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Particle:

It is the point object with infinitesimal size.

Scalar:

The scalar quantity has magnitude (numerical value) but no direction

Example: mass, time, distance (length), temperature.

Vector:

A vector quantity has both magnitude and direction

Example: velocity , acceleration ( , displacement .

Velocity:

It is the rate of change of displacement

Average velocity:

Ratio of change in displacement () to change in time () is called average velocity

Instantaneous Velocity:

Limiting value of the ratio

as time approaches zero is called instantaneous velocity

Time (sec)

Displacement(m)

It is time rate of change of displacement


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Acceleration:

It is the time rate of change of velocity

Average Acceleration:

Ratio of change in velocity ( ) to change in time (

Instantaneous Acceleration:

Limiting value of the ratio

as the time ( approaches zero

Graph

The acceleration of freely falling bodies is constant i.e.

a = slope of V-t graph


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Mohammad Akhtar Kamran Page 1

KINEMATIC EQUATIONS

For accelerated motion

Second Equation of Motion


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Motion with constant acceleration-Calculation of distance travelled in a given time


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QUIZ:

What is the density of earth?

Solution:Mass of earth:

Radius of Earth:

Volume of Earth:

Density:

OR


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GRAPHICAL REPRESENTATION OF MOTION

Graph between position and time

For freely falling body

When the ball is thrown upward, the height increases with time to a maximum and then

decreases to zero

Slope (V) is the time rate of change of height ()

0

5

10

15

20

25

30

35

0 1 2 3 4 5

Distance(Y-axis)VsTime(X-axis)

Xx1

Position

X7

X6

X5

X4

X3

X2

X1

Time -t

At top:

Slope (V) = 0

At the end of curve

Slope steep downward and

represents the maximumdownward velocity

At the start of curve

Slope steep upward and represents

maximum upward velocity


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Graph between Velocity and time

The acceleration of freely falling body is constant

0 2 4 6 8 time

25

20

15

10

05

0

Velocity ms-1

0 1 2 3 4 5 6 Time (sec)

25

20

15

10

05

0

Acceleration

m.sec2

Constant acceleration g=9.8m.s-2

It means that acceleration is not changing


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Example-1:

The speed of sound in air is about 1100ft/sec. if the lightning strikes 1-mile from you and

produces thunder, how long will it take for the sound to reach you?

Solution:

Example-2:

If a falling object increases its velocity from 40m/sec to 60m/sec in 2 seconds then?

a. What is the acceleration?b. What is the average velocity during the interval?c. How far will it travel during the time?

Solution:

a).

b).


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c).

Distance travelled (s)?

()

Example-3:

a. Convert 20ft to inches

b. Convert 20ft to meter

c. Convert 1 mile to meter

Solution:

a. ( )

b. ( )


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c.

( )

THE CAUSE OF MOTIONDO YOU KNOW?

Isaac Newton (1942-1727) formulated three basic laws of mechanics These laws explain the behavior of moving object Einsteins theory of light explains the behavior of objects moving with velocities

near speed of light

MAX Planks Quantum theory is used for the description of the motionmicroscopic particles of atom and nuclei.


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Newtons LawsNEWTONS FIRST LAW OF MOTION:

An object will remain at rest or in uniform motion in a straight line unless some net

external force acts upon it.

Newtons first law of motion is also called Law of Inertia

REST:

An object is at rest if it does not change its position with respect to surroundings

MOTION:

An object is in a state of motion, if it changes its position with respect to surroundings

Quiz:

At rest or motion, who can tell?

Newtons Second Law:

The acceleration of an object is directly proportional to the net external force exerted

upon it and inversely proportional to its mass


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Force (F):

It is an agency which tends to change the state of motion or rest of an object

Mass (m):Mass of an object is a measure of the amount of matter in it and is a measure of its

inertia

It does not change, in a state of motion

It is a scalar quantity

Inertia:It is a resistance to change the state of rest ot sate of motion.

Larger the mass, greater the inertia Smaller the mass, smaller the inertia

Example:

If a man exerts a force of 100 Newton on a crate of mass 5kilogram, initially at rest, in

the absence of friction, Find (a) acceleration (b) speed and distance after 3 seconds.

Solution:

a)

b)

()


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Newtons third Law of Motion

When one body exerts a force on a second body, the second body exerts an equal

but oppositely directed reaction force on the first body

For every action there is an equal and opposite reaction.

F=100N


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Its the Law!

F12 = - F21

Example:

If a 2Kg mass is acted upon by a force of 10N what is the acceleration? If it is initially at

rest, what will be its velocity after 3seconds?

Solution:

a.

b.


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Example:

Centripetal force keeps a car on a circular track

Centripetal force keeps the earth to move around the sun

In the absence of centripetal force, an object leaves the circular path and travel

in the straight line according to Newtons law

Centripetal force in term of angular velocity

Centrifugal force (center fleeing force)

Force required to keep an object moving, away from center of circle is called

centrifugal force.

This force is equal and opposite of centripetal force

Clinical Application of Circular Motion:


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Laboratory centrifuge separate material according to their densities. Heavier particle in centrifuge will move to the outside. Less force will be required

to keep them moving in a circle as radius is larger.

It is used in separating material of different densities. It can be used to measure densities Ultracentrifuges are important tools in microbiology research, its speed

It is used to separate different type of proteins from cellular material

Forces as Vectors

Forces (F=ma) is a vector quantity and has both magnitude (numerical value) and

direction

There are several forces acting in different directions on a single object

Net external force is the sum of all the forces acting on an object i.e. The vector sum of two 50pound forces directed in opposite direction is zero.

( ) When two forces act at right angles, the resultant forces can be obtained by using

Pythagorean Theorem

PerpendicularHypoteneous

Base

4

2


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The diagonal of a rectangle gives the direction of resultant force. The angle ( ) can bemeasured by protractor.

Knee flexion abduction force vector diagram

Resultant Force

1 2 3


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The force of gravityThe earth attracts all objects towards its center due to gravity

Newtons law of gravitation:

It states that every object attracts every other object with the gravitational force, whichis proportional to the product of their masses and inversely proportional to the square of

distance between them

***REPAIRED***

R= distance between centers of masses

G= proportionality constant= 11 22

r

Earth

Stone

F on earth

F on stone


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Weight:

The weight of an object is defined as the force of gravity acting upon it

Weight Density

It is the weight per unit volume

Specific Gravity:

Ratio of density of material to density of water

Earth

MOON

Earth


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Example-1: What is the weight of 10kilogram object?

Solution:

m = 10Kg W = mg

g = 9.8N/Kg W= 10Kg 9.8N/Kg = 98N

Example-2: If a person has a mass of 5slug, What is his weight?

Solution

m = 5slug IN = mg

g = 32 Pound/slug W = 5slug 32 Pound/slug = 160 Pounds

Example-3Volume of a 100 gram block of aluminum is 37cm3. What is the density of

aluminum block?

Solution

Clinical Application of Gravity

Due to the downward pull of gravity, all objects tends to move to the lowestpossible position

Gravity drainage is used to remove fluid from the lungs The gravitational force provides the pressure for administration of intravenous

fluid, transfusion and so on

The force of gravity has an effect upon the circulation of fluid Because of gravitational Pull, the pressure in the blood vessels of legs and feet is

higher than that in head and neck and people have edema of the feet and legs

due to standing for long time

The gravity effect can be seen in the veins of arms and hands if the arms are lefthanging for long period

The improve gravity drainage, post-operative patient are often placed in specialposition.

Brain surgery may be performed in sitting position to lessen the danger ofhemorrhage.

The head may be elevated after surgery for drainage of blood from the brain.

Chapter 2and 3 Final

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