Transcript Slide 1

I. The First 2 Laws of Motion
A. Newton’s Laws
Sir Isaac Newton (1642–1727) able to
state rules that describe the effects of
forces on the motion of objects
B. The First Law of Motion
An object moving at a constant velocity
keeps moving at that velocity unless an
unbalanced net force acts on it (LAW OF
INERTIA)
C. Inertia & Mass
--inertia-- the tendency of an object to
resist any change in its motion
- If object is moving  it wants to keep
moving
- If object is at rest  it wants to stay at
rest
UNLESS……
…UNBALANCED forces act on it!
-The velocity of an object remains
constant…
UNLESS…
…a force changes it!
-The inertia of an object is related to its
mass
The greater the mass of an object
the greater its inertia
-- mass -- the amount of matter an object
has
-- weight -- the amount of mass PLUS
the force of gravity acting on an object
Force is calculated using units of
m/s² AND kg (or g)  these units
combine into a unit called a
NEWTON (mass + acceleration)
D. The Second Law of Motion
The acceleration of an object is in the
same direction as the net force on the
object
Newton's
2nd Law of
Motion
Demo
1.) Force & Acceleration
-Acceleration can be calculated from the
following equation:
Newton's Law's of Motion Song
- Another Maaaaagic
Triiiiangle!
(*oooohhh…aaaaahhhh*)
UNIT USED for
FORCE:
NEWTONS (N)
Force = mass x
acceleration
REMEMBER: acceleration is the change
in velocity divided by the time it takes for
the change to occur 
HINT: Now for problems you may have to solve for
acceleration first before dividing the force!!!
2.) Mass & Acceleration
-The acceleration of an object depends
on its mass as well as the force exerted
on it
- MASS vs. WEIGHT
 An object will always have the same
MASS (amount of matter) no matter
where that object is….Translation:
MASS STAYS THE SAME!
 An object’s WEIGHT (mass + force
of gravity) may be different in different
places in the universe because of
different forces of
gravity…Translation: WEIGHT CAN
CHANGE!
Bill Nye: Mass vs. Weight & Momentum
II. Gravity
A. What is Gravity?
-- gravity -- attractive force between any
2 objects
 depends on the
masses of the objects &
the distance between
them
Increasing mass
increases an objects
gravitational force!
Decreasing distance
between objects
increases gravitational
force!
1.) Gravity- A Basic Force
The “Big 4” Basic Forces:
GRAVITY
ELECTROMAGNETIC FORCE
STRONG NUCLEAR FORCE
WEAK NUCLEAR FORCE
B. Law of Universal Gravitation
G  universal gravitational constant
d  distance between two masses
m1 & m2  the two masses
TRANSLATION:  Law of Universal
Gravitation enables the force of gravity
to be calculated between any 2 objects if
their masses & the distance between
them is known
1.) Range of Gravity
- No matter how far apart 2 objects are,
the gravitational force between them
never completely goes to zero
 gravity is a LONG-RANGE FORCE
Nye Tunes "G-R-A-V-I-T-Y"
C. Earth’s Gravitational Acceleration
- When all forces except gravity acting
on a falling object can be ignored, the
object is said to be in free fall
-Close to Earth’s surface, the
acceleration of a falling object in free fall
2
is about 9.8 m/s
- Symbol for acceleration of gravity  g
-By Newton’s 2nd law of motion force of
Earth’s gravity on a falling object =
object’s mass times the acceleration of
gravity… F = m x g
UNIT USED = NEWTONS (N)
1.) Weight
***Weight is a force ***
***Mass is a measure of the amount of
matter an object contains***
D. Weightlessness & Free Fall
1.) Floating in Space
- If gravitational forces never disappear
 how does one become “weightless”
(example: astronauts in space)?
Objects will seem to float because they
are all falling with the same acceleration
 astronaut & ship are falling towards
Earth but falling at the SAME RATE
Fun in Space- Zero Gravity - NASA footage
E. Projectile Motion
- Earth’s gravity causes projectiles to
follow a curved path
1.) Horizontal & Vertical Motion
-When you throw a ball force exerted
pushes the ball forward to give it
HORIZONTAL MOTION
-Horizontal Velocity of ball is constant
(*ignoring air resistance*)
-When you let go of the ball, gravity pulls
it downward giving it VERTICAL
MOTION  ball travels in a curve
2.) Horizontal & Vertical Distance
-If a ball as thrown in a perfectly
horizontal direction, would it take longer
to reach the ground than a dropped a
ball from the same height?
NO!!! They would drop
at the same time!
Projectile Motion
-Both balls travel the same vertical
distance in the same amount of time 
thrown ball travels a longer horizontal
distance
F. Centripetal Force
- When a ball enters a curve it is
accelerating because its direction is
changing (even if its speed does not
change)
Centripetal
Force demo
-When a ball goes around a curve
change in the direction of the velocity is
toward the center of the curve
--centripetal acceleration-- acceleration
toward the center of a curved or circular
path
--centripetal force-- net force exerted
toward the center of a curved path
1.) Centripetal Force & Traction
-A car rounds a curve on a highway
centripetal force acts on the car to keep
it moving in a curved path
 Centripetal Force is the frictional force
(traction) between the tires & road
surface
III. Newton’s Third Law
When one object exerts a force on a
second object the second one exerts a
force on the first that is equal in strength
& opposite in direction
Bill Nye & Newton's 3rd Law
A. Action & Reaction
- When a force is applied in nature a
reaction force occurs at the same time
-Even though the forces are equal, they
are not balanced because they act on
different objects
EXAMPLE: A
swimmer “acts” on
the water, the
“reaction” of the
water pushes the
swimmer forward
Action and Reaction
 a net force, or
unbalanced force,
acts on the swimmer
so a change in their
motion occurs
B. Momentum
--momentum-- a product of mass &
velocity
- Momentum symbol  p
- Unit for momentum kg · m/s
1.) Force & Changing Momentum
-By combining acceleration equation &
force equation Newton’s 2nd Law
Equation:
***Final Momentum  mvf
***Initial Momentum  mvi
C. Law of Conservation of
Momentum
-Momentum of an object doesn’t
change….
…UNLESS
…its mass,
velocity, or
both change!
Newton's Cradle
-Momentum can be transferred from one
object to another!
Law of Conservation of Momentum: If a
group of objects exerts forces only on
each other their total momentum
doesn’t change
1.) When Objects Collide
- Results of a collision depend on the
momentum of each object
- When an object hits
another from behind
 momentum occurs
in the SAME direction
- When an object
hits another head
on with the same
force 
momentum is
ZERO
- If one object hits another head on with
the more/less force  momentum is
TRANSFERRED