4. 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.
5. 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.
6. 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.
9. 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)
10. 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.
13. 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. The
Earth is so massive, its acceleration is much smaller than the ball,
so it’s impossible to see.
16. 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.
17. 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.
