2. Laws of Motion
 An object at rest can be moved by applying an external
force on it.

3. What Are Newton’s Laws of
Motion?
 Galileo was the first to suggest that uniform speed or
straight-line motion was just as natural as at-rest state
of motion.
 Galileo’s work profoundly influenced Sir Isaac Newton,
the originator of the laws of motion.

4. Balanced and Unbalanced Forces
 Forces can produce changes in motion. There is a
change in motion when:
 an object at rest starts to move,
 an object in motion changes speed,
 an object in motion stops.
The forces that is capable of changing the state of
motion of an object is called net force.
Force can speed up or slow down a moving object. It
produces an acceleration(vector quantity).

5.  The net force is zero when the two forces are equal and
they act in opposite directions.
 These forces are said to be balanced forces.
An unbalanced force, on the other hand, is a nonzero net
force. An unbalanced force or net force produces
acceleration.

6. Law of Inertia
 Galileo defined inertia as the tendency of an object to
maintain its initial state of motion.
 Originally, Newton called mass a quantity of matter,
but later redefined it as a measure of inertia.
 Inertia states that a body at rest
remains at rest, and a body already
in motion remains in motion with a
constant velocity, in the absence of
an unbalanced applied force.

8. Law of Acceleration
 When there is a net force, how does the velocity of the
object change?

9.  Law of Force and Acceleration, a force upon an
object causes it to accelerate according to the
formula net force = mass x acceleration. So the
acceleration of the object is directly proportional to
the force and inversely proportional to the mass.
 The acceleration of an object as produced by a net
force is directly proportional to the magnitude of the
net force, in the same direction as the net force, and
inversely proportional to the mass of the object.
 As the force acting upon an object is increased, the
acceleration of the object is increased. As the mass of
an object is increased, the acceleration of the object is
decreased.

10. Units of Mass, Acceleration and
Force
System Quantity Mass Acceleration Force
MKS kg m/𝑠2
𝑁 = 𝑘𝑔⦁𝑚/𝑠2
CGS g 𝑐𝑚/𝑠2
𝑑𝑦𝑛𝑒 = 𝑔⦁𝑐𝑚/𝑠2

11.  For every action, there is an equal and opposite
reaction.
 A force is a push or a pull that acts upon an object as a
results of its interaction with another object. Forces
result from interactions!
The Law of Interaction

12. Exercise #1
 What law of motion is illustrated by:
1. a rifle that coils when fired?
2. a truck that has a more powerful engine than a small
compact car?
3. a rocket that lifts off from a space-shuttle system?
4. a runner who goes on running for sometime even as
he reaches the finish line
5. A man is propelled upward and then down into the
swimming pool as he jumps on the diving board.

13.  One's body movement to the side when a car makes a
sharp turn.
 Skating
 As you walk, you exert a force against the floor (down
and backward); the floor exerts a force back (up and
forward), causing you to move forward.
 Men in space find it more difficult to stop moving
because of a lack of gravity acting against them
 pulling a crate along a concrete floor
 A ball rolling down a hill will continue to roll unless
friction or another force stops it.
 Where a fireman puts off a fire, he has to hold on
tighly to the fire hose.

14. • standing still in a stationary train, then suddenly it
moves forward
• Supposed you are on a trip with your family. Then
suddenly, your car ran out of gas and stopped. You
need to push it to the side of the road.

15.  Keywords
 A net force is capable of
changing the state of motion
of an object
 Acceleration is the rate of
change in velocity of a moving
object per unit of time.
 Velocity-description of the
motion of an object in terms
of both the speed and
direction

16.  Balanced forces are equal
forces acting in opposite
directions; thus, they have
zero net force.
 An unbalanced force has a
nonzero net force; thus it
produces acceleration.