Newton's Laws of Motion describe the relationship between an object and the forces acting on it. The first law states that objects at rest stay at rest and moving objects stay moving unless acted upon by an unbalanced force. The second law explains that acceleration depends on the net force acting on an object and its mass. The third law states that for every action force there is an equal and opposite reaction force. These laws describe the fundamentals of classical mechanics.

2. Newton’s Laws of Motion
• In 1686, Sir Isaac
Newton explained
the relationship
between force
and the motion of
objects with
three laws of
motion.

3. 1st Law of Motion
• Newton’s 1st Law of Motion
states that an object at rest
remains at rest and an
object in motion stays in
motion until acted on by an
unbalanced force.
• Two parts: Objects at rest
and objects in motion.
• Part 1: A golf ball will remain
on the tee until the golf club
(unbalanced force) comes
into contact with it.

4. 1st Law continued
• Part 2: Bumper cars remain
moving at the same speed and
in the same direction until an
unbalanced force acts on it.
• Often, this force is another
car, which transfers force
and causes the other car (and
yourself since you’re strapped
in) to change direction.
• Friction is also an unbalanced
force acting in the opposite
direction of a moving object.
– Demonstration

5. Inertia
• Newton’s 1st Law is often called
the law of inertia.
• Inertia is the tendency of all
objects to resist any change in
motion.
• All objects (resting or in motion)
have inertia.
• Objects with a smaller mass have
less inertia than one with a
larger mass. It’s easier to start
and stop a less massive object.
– Mass is a measure of inertia.

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7. Newton’s 2nd Law of Motion
• Newton’s 2nd law states that
the acceleration of an object
depends on the mass of the
object and the amount of
force applied.
• Part 1: Acceleration depends
on mass.
– An empty shopping cart
accelerates faster than a full
cart. Acceleration increases as
mass decreases and acceleration
decreases as mass increases.
(inverse relationship)

8. Newton’s 2 Law continued
nd
• Part 2: Acceleration depends on force.
– The same cart will move faster when a larger amount
of force is used. Acceleration increases as force
increases. (direct relationship)
• Mathematically, Newton’s 2nd law states:
– a = F/m or F = ma
– Acceleration equals the force applied divided by the
object’s mass. When rearranged, force equals the
object’s mass multiplied by acceleration.
• This law explains why objects fall to Earth at
the same rate regardless of mass.

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10. Newton’s 3rd Law of Motion
• Newton’s 3rd law states that whenever an
object exerts a force on a second object,
the second object exerts an equal and
opposite force on the first object.
• The law states that forces act in pairs,
but do not act on the same object.
• There are action and reaction forces
(acting in pairs).
• Example: A swimmer’s arms act on the
water. The water reacts by pushing on
the arms, hand, and feet which moves the
swimmer forward.
• Effects of a Reaction force can be
difficult to see.
– When a ball falls to Earth, gravity pulls the ball
(action force). The reaction force is gravity
pulling Earth towards the ball (reaction force).
The Earth is so massive, its acceleration is much
smaller than the ball, so it’s impossible to see.

11. 3rd Law Continued
For every action there is an
equal & opposite reaction.

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13. Momentum
• Momentum is a property of
moving objects that
depends on the object’s
mass and velocity.
• If a small car and truck are
traveling with the same
velocity, the truck has
greater momentum due to
its larger mass and will be
harder to stop.
• Similarly, if two cars are
traveling with different
velocities, the car with a
greater velocity has greater
momentum than the smaller
car.

14. Conservation of Momentum
• When a moving object hits
another object, some or all
of the momentum from the
first object is transferred
to the other object.
• For example: Billiards and
Bowling
• Law of Conservation of
Momentum: Any time two or
more objects interact, they
may exchange momentum,
but the total amount of
momentum stays the same.