The Questions
1. What does Net Force mean?
2. What is Newton’s 1st Law?
Force changes motion
A force is a push or pull
BUT
IT IS THE “NET FORCE” THAT WE CARE ABOUT!!
Net Force
Net Force is the sum of
the forces acting on an
object in EACH direction
(x or y).
What is the Net Force
acting on the golf ball??
x-Direction:
(+20N) + (-10N) = +10N
y-Direction:
(+5N) + (-5N) = 0N
+20N
-10N
-5N
Gravity
+5N
(+300N) + (+300N) = +600N
(+Normal Up) + (-Gravity down) = 0N
Is this object in Equilibrium?
Newton’s 1st Law: The Law of Inertia
 Official Version:
“An object at rest will stay at rest and
an object in motion will continue in
motion at a CONSTANT VELOCITY
unless acted on by a NON-0 Net force.”
Newton’s 1st Law: The Law of Inertia
Newton’s 1st Law in simple English:
 Objects that are not moving will not move
unless pushed by a non-0 NET force.
Objects that are moving will keep moving at
the same velocity unless a non-0 NET force
pushes on them.
If the Net Force on an object is 0N, an object
at rest (velocity=0m/s) will stay at rest
(velocity=0m/s).
If an object is acted upon by an unbalanced
force (Net Force ≠0), its motion (VELOCITY)
will change.
Newton’s 1st Law: The Law of Inertia
Inertia is a property of
matter!
Who said this??
 Billy Nye
Inertia is the property of an
object that resists changes in
motion (VELOCITY).
Inertia = mass
Inertia is the same thing as
an objects mass.
Which ball has more inertia?
Inertia is measured with
kilograms.
Bowling Ball
The Answers
1. What does Net Force mean?
a) The sum of all of the forces
acting on an object.
2. What is Newton’s 1st Law?
a) Known as the “Law of Inertia”
b) An object’s velocity will change if
the net force is not 0.
Newton’s First Law is known as:
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1. Law of Action and
Reaction
2. Law of Conserved
Mass
3. Law of Inertia
4. Law of Conserved
Energy
5. Law of the Benevolent
Dictator
Inertia is measured in units of
1. Meters
2. Liters
3. Kilograms
4. Seconds
5. N/kg
6. m/s2
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What has more Inertia?
1. Baseball
2. Skyball
3. Bowling Ball
4. Beach Ball
5. Golf Ball
6. Ping Pong Ball
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A Net Force of +100N acts on an
object. That object will
1. Stay in motion.
2. Stay at rest.
3. Have its velocity
changed.
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