Newton's Three Laws of Motion

1. Newton’s
LAWS OF MOTION

2. Objectives
• Identify the different laws of motion
• Understand the concepts of laws of motion
• Give an example about the laws of motion in a real
life scenario

3. Sir Isaac Newton
(1643-1727)
An English scientist and mathematician,
worked in many areas of mathematics and physics.
The three laws of motion describe the motion of
massive bodies and how they interact. He was one
of the most influential scientists of all time. His
ideas became the basis for modern physics.

4. Sir Isaac Newton
(1643-1727)
He built upon ideas put forth from the works of
previous scientists including Galileo and Aristotle and
was able to prove some ideas that had only been
theories in the past. He also studied optics, astronomy
and math — he invented calculus. (German
mathematician Gottfried Leibniz is also credited with
developing it independently at about the same time.)

5. Sir Isaac Newton
(1643-1727)
He developed the theories of gravitation in
1666, when he was only 23 years old. Some twenty years
later, in 1686, he presented his three laws of motion in
the "Principia Mathematica Philosophiae Naturalis."
Today these laws are known as Newton’s Laws of Motion
and describe the motion of all objects on the scale we
experience in our everyday lives.

6. Newton’s Laws of Motion
• An object in motion tends to stay in motion and
an object at rest tends to stay at rest unless
acted upon by an unbalanced force.
• Force equals mass times acceleration (F = ma).
• For every action there is an equal and opposite
reaction.

7. Newton’s First Law
An object at rest tends to stay at rest and an
object in motion tends to stay in motion
unless acted upon by an unbalanced force.

8. Newton’s First Law
What does this mean?
 Basically, an object will “keep doing what it was doing” unless
acted on by an unbalanced force.
 If the object was sitting still, it will remain stationary. If it was
moving at a constant velocity, it will keep moving.
 It takes force to change the motion of an object.

9. Newton’s First Law
Inertia
 Inertia is a term used to measure the ability of an object to
resist a change in its state of motion
 An object with a lot of inertia takes a lot of force to start or
stop; an object with a small amount of inertia requires a small
amount of force to start or stop.
 The word “inertia” comes from the Latin word inertus, which
can be translated to mean “lazy.”

10. Newton’s First Law
Newton’s First Law is also called the Law of Inertia
Inertia: the tendency of an object to resist changes in its state of
motion
The word “inertia” comes from the Latin word inertus, which can
be translated to mean “lazy.”
The First Law states that all objects have inertia. The more mass
an object has, the more inertia it has (and the harder it is to
change its motion).

11. Newton’s First Law
If objects in motion tend to stay in motion, why don’t
moving objects keep moving forever?
Things don’t keep moving forever because there’s almost always
an unbalanced force acting upon it.

12. Newton’s First Law
What is meant by unbalanced force?
If the forces on an object are equal and
opposite, they are said to be balanced,
and the object experiences no change in
motion.
If they are not equal and opposite, then
the forces are unbalanced and the
motion of the object changes.

13. Newton’s First Law
Some Examples from Real Life
A soccer ball is sitting at rest. It takes an
unbalanced force of a kick to change its
motion.

14. Newton’s First Law
Some Examples from Real Life
Don’t let this be you. Wear seat
belts. Because of inertia, objects
(including you) resist changes in
their motion. When the car
going 80 km/hour is stopped by
the brick wall, your body keeps
moving at 80 km/hour.

15. Newton’s First Law

18. Newton’s First Law
More Examples from Real Life
On your way to school, a bug flies into
your windshield. Since the bug is so
small, it has very little inertia and
exerts a very small force on your car (so
small that you don’t even feel it).

19. Newton’s First Law
A book sliding across a table slows
down and stops because of the force of
friction.

20. Newton’s First Law
If you throw a ball upwards it will
eventually slow down and fall because
of the force of gravity.

21. Newton’s First Law
In outer space, away from gravity and
any sources of friction, a rocket ship
launched with a certain speed and
direction would keep going in that
same direction and at that same speed
forever.

22. Newton’s Second Law
Force equals mass times acceleration.
F = ma
Acceleration: a measurement of how quickly
an object is changing speed

23. Newton’s Second Law
Force equals mass times acceleration.
F = ma
Acceleration: a measurement of how quickly
an object is changing speed

24. Newton’s Second Law
•An unbalanced force causes something to accelerate.
•A force can cause motion only if it is met with an unbalanced force.
•Forces can be balanced or unbalanced.
•Depends on the net force acting on the object
•Net force (Fnet): The sum total and direction of all forces acting on the
object.
•Net forces: Always cause acceleration.

25. Newton’s Second Law
Balanced Versus Unbalanced
Balanced forces cause no
acceleration.

26. Newton’s Second Law
Balanced Versus Unbalanced
Unbalanced forces cause
acceleration.

27. Newton’s Second Law
What does F = ma mean?
Force is directly proportional to mass and acceleration. Imagine a
ball of a certain mass moving at a certain acceleration. This ball
has a certain force.
Now imagine we make the ball twice as big (double the mass) but
keep the acceleration constant. F = ma says that this new ball has
twice the force of the old ball.
Now imagine the original ball moving at twice the original
acceleration. F = ma says that the ball will again have twice the
force of the ball at the original acceleration.

28. Newton’s Second Law
What does F = ma mean?
If you double the mass, you double the force. If you double the
acceleration, you double the force.
What if you double the mass and the acceleration?
(2m)(2a) = 4F
Doubling the mass and the acceleration quadruples the force.

29. Newton’s Second Law
What does F = ma mean?
• F = ma basically means that the force of an object comes from
its mass and its acceleration.
• Force is measured in
• Newtons (N) = mass (kg) x acceleration (m/s2) Or kg m/s2

30. Newton’s Second Law

31. A net force of 10 Newtons acts on a box which has a
mass of 2 kg. What will be the acceleration of the
box?

32. How much horizontal net force is required to
accelerate a 1000 kg car at 2 m/s2?

33. A delivery man pushes a box with a net force of 1000 N
and the box slides at a rate of 50 m/s in 10 seconds.
Determine the box’s mass.
a=v/t=50/10=5
m=F/a=1000/5= 200 kg

34. Newton’s Third Law
For every action there is an equal and
opposite reaction.

35. Newton’s Third Law
What does F = ma mean?
• For every force acting on an object, there is
an equal force acting in the opposite
direction. Right now, gravity is pulling you
down in your seat, but Newton’s Third Law
says your seat is pushing up against you with
equal force. This is why you are not moving.
There is a balanced force acting on you–
gravity pulling down, your seat pushing up.

36. Newton’s Third Law
Think about it . . .
What happens if you are standing on a
skateboard or a slippery floor and push against a
wall? You slide in the opposite direction (away
from the wall), because you pushed on the wall
but the wall pushed back on you with equal and
opposite force.

37. Newton’s Third Law
Think about it . . .
Why does it hurt so much when you stub your
toe? When your toe exerts a force on a rock, the
rock exerts an equal force back on your toe. The
harder you hit your toe against it, the more force
the rock exerts back on your toe (and the more
your toe hurts)

38. Newton’s Third Law
Think about it . . .

39. Newton’s Third Law
Forces and Interactions
Newton’s third law describes the relationship between two forces in
an interaction.
•One force is called the action force.
•The other force is called the reaction force.
•Neither force exists without the other.
•They are equal in strength and opposite in direction.
•They occur at the same time (simultaneously).

40. Newton’s Third Law
Forces and Interactions
When the girl jumps to shore,
the boat moves backward.

41. Newton’s Third Law
Identifying Action and Reaction Pairs
When action is A exerts force on B, the reaction is simply B exerts
force on A.

42. Newton’s Third Law

43. Newton’s Third Law

44. Quiz
1.What is Newton's second law of motion?
a. For every action, there is an equal and opposite reaction. The statement
means that in every interaction, there is a pair of forces acting on the two
interacting objects
b. 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.
c. An object at rest will stay at rest and an object in motion will stay in
motion with the same speed and direction unless acted upon by
unbalanced force.

45. Quiz
2. If you use the same force to push a truck and push a car which one
will have more acceleration and why?
a. The truck
b. The car
c. Both
d. None of the above

46. Quiz
3. A sled sliding on a flat, icy surface with a constant velocity is best
described by
a. Newton’s first law of motion for objects at rest.
b. Newton’s second law of motion.
c. Newton’s first law of motion for objects in motion.
d. Newton’s third law of motion.

47. Quiz
4. Forces always act in equal and opposite pairs.
a. Newton's 1st Law
b. Newton's 3rd Law
c. Newton's second law

48. Quiz
5. Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to
push the car to a gas station, and he makes the car go 0.05 m/s/s.
Using Newton's Second Law, you can compute how much force Mike
is applying to the car.
a. 50 N
b. 20 N
c.100 N
d. 5 N