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Lecture 1 Applications of Newton Laws

Course Title : Applied Physics
Course Code: PHY-102
Credit hours: 3(2-1)
Text Book:
1. Physics by Halliday, Resnick, Krane, 5th edition, Vol-I & Vol-II
2. Physics for Scientists and Engineers 8th Ed Raymond A. Serway
Reference Books:
1. Physics By Halliday, Resnick& Walker (7th Edition)
2. University Physics, 12th Edition by Hugh D.Young, Roqer A. Freedman
and Lewis Ford
3. Physics for Scientists & Engineers, 6th edition (extended version) by Paul
A.Tipler and Gene Mosca
Program Learning Outcomes
Course Learning Outcomes CLOs
Grading Scheme
Mid Semester Exam
End Semester Examination
Lecture 1
Force: What is force
 Types of Forces
 Review of Newton Laws
 Application of Newton Laws
• Force: push or pull.
• Force is a vector – it has magnitude and direction
Newton’s First Law of Motion
• Newton’s First Law: If no net force acts on a body(Fnet=0) , the body’s
velocity cannot change; that is, the body cannot accelerate.
• If you stop pushing an object, does it stop moving?
• Only if there is friction! In the absence of any net external force, an
object will keep moving at a constant speed in a straight line, or remain
at rest.
• This is also known as the law of inertia.
• In order to change the velocity of an object – magnitude or direction – a
net force is required.
5-3 Newton’s Second Law of Motion
Now that we have a calibrated spring, Acceleration is inversely proportional to mass:
we can do more experiments.
Acceleration is proportional to force:
Combining these two observations gives
Or, more familiarly,
Newton’s Second Law of Motion
Newton’s Second Law: The net force on a body is equal to the
product of the body’s mass and its acceleration.
An object may have several forces acting on it; the acceleration
is due to the net force:
Newton’s Third Law of Motion
Forces always come in pairs,
acting on different objects:
If object 1 exerts a force Fon
object 2, then object 2 exerts a
force – F on object 1.
These forces are called actionreaction pairs.
Free-body diagrams:
A free-body diagram shows every
force acting on an object.
• Sketch the forces
• Isolate the object of interest
• Choose a convenient coordinate
• Resolve the forces into components
• Apply Newton’s second law to each
coordinate direction
The Vector Nature of Forces: Forces in Two Dimensions
The easiest way to handle forces in two dimensions is to treat
each dimension separately, as we did for kinematics.
Mass and Weight
• Mass is the measure of how hard it is to change an object’s
velocity. Mass can also be thought of as a measure of the
quantity of matter in an object
• The weight of an object on the Earth’s surface is the
gravitational force exerted on it by the Earth.
Normal Forces
• The normal force is the force exerted by a surface on an
• The normal force may be equal to, greater than, or
less than the weight.
• The normal force is always perpendicular to the surface.
Strings and Springs
When you pull on a string or rope, it becomes taut. We say that
there is tension in the string.
Strings and Springs
The tension in a real rope will vary along its
length, due to the weight of the rope.
Here, we will assume that
all ropes, strings, wires,
etc. are massless unless
otherwise stated.
Strings and Springs
An ideal pulley is one that simply changes the direction
of the tension:
Translational Equilibrium
When an object is in translational equilibrium, the net force on it
is zero:
This allows the calculation of unknown forces.
6-3 Translational Equilibrium
Connected Objects
When forces are exerted on connected objects, their
accelerations are the same.
If there are two objects connected by a string, and we know the
force and the masses, we can find the acceleration and the
Connected Objects
We treat each box as a separate system:
Connected Objects
If there is a pulley, it is easiest to have the coordinate system follow the string: