Republic of the Philippines
PARTIDO STATE UNIVERSITY
Camarines Sur
College of Engineering and Computational Sciences
Module 3: Newton’s Law of Motion
I. Learning Objectives
This module aims at the following objectives:
1. Familiarize and understand the three newton’s law of motion.
2. Familiarize the different types of friction.
3. Calculate simple problems involving friction.
4. Perform applications through laboratory experiment.
II. Learning Content
MASS - a measure of the inertia of the object.
Inertia - is the tendency of a body at rest to remain at rest, and of a body in
motion to continue moving with unchanged velocity.
FORCE -in mechanics it is that which changes the velocity of an object.
- a vector quantity, having magnitude and direction.
External force - is one whose source lies outside of the system being considered.
NET EXTERNAL FORCE acting on an object causes the object to accelerate in the
direction of that force.
The acceleration is proportional to the force and inversely proportional to the mass of the
object.
𝑎 = 𝐹/𝑚
3 NEWTON’S LAW OF MOTION
1. NEWTON’S FIRST LAW (LAW OF INERTIA) : An object at rest will remain at
rest; an object in motion will continue in motion with constant velocity, except insofar
as it is acted upon by an external force. Force is the changer of motion.
General Physics/ De Asis 1
Republic of the Philippines
PARTIDO STATE UNIVERSITY
Camarines Sur
2. NEWTON’S SECOND LAW (LAW OF ACCELERATION): The acceleration of
an object is directly proportional to the net force acting on the object, is in the same
direction as the net force, and is inversely proportional to the mass of the object.
A larger net force results in a greater acceleration, while a larger mass results in a smaller
acceleration for the same force.
3. NEWTON’S THIRD LAW (ACTION AND REACTION) : For every action, there
is an equal and opposite reaction.
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Republic of the Philippines
PARTIDO STATE UNIVERSITY
Camarines Sur
THE LAW OF UNIVERSAL GRAVITATION: When two masses m1 and m2 gravitationally
interact, they attract each other with forces of equal magnitude. For point masses (or
spherically symmetric bodies), the attractive force FG is given by;
𝑚1𝑚2
FG = 𝐺 𝑟^2
where r is the distance between mass centers, and where G = б.б7 x 10—11 N m2/kg2 when FG
is in newtons, m and m ' are in kilograms, and r is in meters.
THE WEIGHT of an object FW or W is the gravitational force acting downward on the
object.
𝑾 = 𝒎𝒈
Where:
W = weight
m = mass
g = acceleration due to gravity (9.81 m/s2)
RELATION BETWEEN MASS AND WEIGHT:
- An object of mass m falling freely toward the Earth is subject to only one force — the
pull of gravity, which we call the weight FW of the object.
- The object‘s acceleration due to FW is the free-fall acceleration g.
- Therefore, →F = ma provides us with the relation between F = FW , a = g, and m; it
is FW = mg. Because, on average, g = 9.81 m/s2 on Earth, a 1.00 kg object weighs
9.81 N at the Earth‘s surface.
General Physics/ De Asis 3
Republic of the Philippines
PARTIDO STATE UNIVERSITY
Camarines Sur
THE TENSILE FORCE
- acting on a string or chain or tendon is the applied force tending to
stretch it. The magnitude of the tensile force is the tension (FT ).
THE FRICTION FORCE
- is a tangential force acting on an object that opposes the sliding of that
object on an adjacent surface with which it is in contact.
- parallel to the surface and opposite to the direction of motion or of
impending motion.
- Only when the applied force exceeds the maximum static friction force will
an object begin to slide.
THE NORMAL FORCE
- on an object that is being supported by a surface is the component
of the supporting force that is perpendicular to the surface.
FRICTION
- unbalanced force that opposes or slows down the motion of an object.
- Contact force caused when two objects are touching.
Types of Friction
1. Static – two objects not moving.
2. Sliding – two objects sliding past each other.
3. Rolling – two objects rolling past each other.
4. Fluid – viscous friction
THE COEFFICIENT OF KINETIC FRICTION (µk)
- defined for the case in which one surface is sliding across another at constant
speed. It is
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Republic of the Philippines
PARTIDO STATE UNIVERSITY
Camarines Sur
Example Problem 1
Example Problem 2
The object in the figure weighs 50 N and is supported by a cord. Find the tension in the cord.
Example 3
A 70-kg box is slid along the floor by a 400-N force
as shown. The coefficient of friction between the box
and the floor is 0.50 when the box is sliding. Find the
acceleration of the box.
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Republic of the Philippines
PARTIDO STATE UNIVERSITY
Camarines Sur
Example 4
III. Learning Resources
Bueche, Frederick J., and Eugene Hecht. Schaum's Outline of Theory and Problems of
College Physics. 9th ed., McGraw-Hill, 1997.
“Newton’s Laws of Motion.” Scribd, uploaded by Scribd user, n.d.,
https://www.scribd.com/doc/250325072/newtons-laws-of-motion. Accessed 13 June
2025.
General Physics/ De Asis 6
