Download Aristotle on Motion

Bell Ringer
Describe one station from
yesterday’s lab in detail.

Bell Ringer
What is the
difference between
weight and mass?

NEWTON’S
FIRST LAW
MOTION
•
Laid the groundwork for Isaac
Newton to develop his motion laws
– Force: Any push or pull
– Friction: Force acting between
materials that touch as they move
past each other
• Always opposes direction of
motion
MOTION
•
Concluded that the tendency of a
moving object to keep moving is
natural
– Inertia: The property that every
object has to resist changes to
its state of motion
MOTION
Bell Ringer

Give an example where inertia
plays a role on the motion of an
object.
LAW
An object in motion will stay
in motion, and an object at
rest will stay at rest unless
acted upon by a net, external
force
• Objects tend to keep doing what
they’re already doing
• Also called the Law of Inertia
MASS
•
Mass: A measure of the amount of
inertia an object possesses
– The
•
amount of matter in an object
Units of Mass
– Metric
System: grams (g), kilograms
(kg)
– English System: slugs
MASS IS NOT
VOLUME
Volume: The amount of space an
object takes up
• Units of Volume
– Metric System: liter (L), milliliter
(mL)
– English System: quart, gallon…
•
WEIGHT
Weight Equation:
weight = mass x gravity
•
So on Earth, 1 kg weighs 9.8 N
NET FORCE
The combination of all forces acting on
an object
• In the absence of a NET force:
– Objects at rest, stay at rest
– Objects in motion, stay in motion
• Vector addition is used to find the net
force acting on an object
•
NET FORCE
Bell Ringer
Which has more inertia 0.5 g
fly or a 50,000 g bowling
ball?
 How much does the bowling
ball weigh?
 How much does the fly
weigh?

EQUILIBRIUM
When the net forces on an object
•
sum to zero
• Objects in equilibrium are either:
– At rest
– In motion at constant velocity
• Objects require a net force in
order to accelerate
DIAGRAMS
FBDs isolate the object of
interest and analyze only the
forces acting on the object
• They are necessary to analyze
the motion of an object due to
the forces acting on it
•
DIAGRAMS
DIAGRAMS
Pushing Force
(FP)
Frictional Force
(Ff)
Normal Force
(FN)
Weight Force
(FW)
Newton’s
Second Law
Newton’s Second Law
Force causes acceleration
Force and acceleration are
proportional
As one increases, the other
increases by the same amount
Newton’s Second Law
Mass resists acceleration
Objects with more inertia are less
likely to change their states of
motion
Acceleration is inversely
proportional to mass
As mass increases, acceleration
decreases by the same amount
Newton’s Second Law
Force is equal to mass times
acceleration
SF = ma
Where:
 SF = net force in Newtons
m = mass in kilograms
a = acceleration in m/s2
Newton’s Second Law
Note: The acceleration is
always in the same direction
as net force
Bell Ringer
•What is the mass of a
student who weighs
680N?
•What is their mass on
2
the moon? (1.62m/s )
Bell Ringer
•Draw the FBD of a car
stepping on the gas
while going up a hill
Bell Ringer
• A bug smashes into a truck’s
windshield as it is driving at
80 mph. SWAAP!!
• Which object experiences a
larger force?
Newton’s Second Law
Force is equal to mass times
acceleration
SF = ma
Where:
 SF = net force in Newtons
m = mass in kilograms
a = acceleration in m/s2
Thought Question
• An old frail man approaches a worn bridge
with his horse and wagon. He is worried that
the tattered bridge will not hold up his wagon
full of many rare and exotic birds. He ponders
for a moment about what he can do in his
dilemma and comes up with a solution. He
swiftly shakes the bird cage and safely crosses
the bridge.
– What did this do?
Pressure
Pressure: The amount of force per
unit area
• No matter what position you place
a block on a table, it still applies
the same force (weight) on that
table
Pressure
• To reduce pressure, you want to
exert a large force over a large area
• Pressure is calculated using the
equation:
Pressure = Force / Area
OR
P = F/A
• Units: N/m2 or Pascals (Pa)
Why do camels have
such big feet?
Larger surface
area to
distribute the
force so they
don’t sink into
the sand
Bell Ringer 10/6
•What is Newton’s
Law?
nd
•What is Newton’s 2
Law?
st
1
Friction
Not restricted to solids, occurs
in gases and fluids as well
To move an object at constant
velocity
With Friction: An outside force
must balance out the frictional
force, making the net force zero
Without Friction: An outside, net
force is NOT needed (still making
the net force zero)
Freefall Explained
Solving F = ma for a, we get:
F
a= m
The force of gravity and mass of an
object are proportional and = to g
F
m
and
F
m
Freefall and Air
Resistance
Freefall and Air
Resistance
Air resistance is a force that
counteracts the weight force for
objects in freefall
Consider a hammer and a feather:
Unlike the hammer, the feather has a
small weight, so air resistance quickly
builds to equal its weight
Freefall Explained
When air resistance equals the
weight force, the net force acting is
zero, and the object stops
accelerating
This is known as terminal velocity
Freefall and Air
Resistance
For a constant shape:
Heavy objects take longer to reach
terminal velocity than lighter objects
For a constant weight:
Smaller surface areas take longer to
reach terminal velocity than larger
surface areas
Freefall and Air
Resistance
Freefall and Air
Resistance
Bell Ringer
•Why do heavier
bodies “appear” to
be falling faster than
lighter ones?
Review Question
• How much does a 60 kg
person weigh?
• How much force is required
to lift this person?
Newton’s
Third Law
Forces and Interactions
• Forces do not act alone
• They are interactions: Mutual
actions between two objects
• 2 forces will always act as
partners (in pairs)
Forces and Interactions
• Unlike mass, objects do not
naturally possess force
• Newton’s
rd
3
Law states:
Every action has an equal
and opposite reaction
Identifying ActionReaction Pairs
• The “formula”:
• ACTION: Object A exerts a
force on object B
• REACTION: Object B exerts
a force on object A
Different Masses
• Forces acting on different objects
are ALWAYS equal and opposite
• It is mass that causes objects to
behave differently
• According to Newton’s 2nd Law,
varying the mass to which the
force is applied will vary its
acceleration
Different Masses
Consider the following:
• A cannon has mass = m
• A cannonball has mass = m
• When fired, the cannon applies
a force to the cannonball that is
equal and opposite to the force
the cannonball applies back on
the cannon
Different Masses
So why does the cannonball have a
large acceleration while the cannon
recoils only slightly?
CANNONBALL:
CANNON:
F/m = a
F/m = a
Given the same force, smaller
masses will accelerate at a greater
rate
Bell Ringer
What is the
action/reaction pair
for a skydiver
jumping out of a
plane?

Rocket Final Build Day






Review your rubric
Test your recovery system
Fit your rocket for the launcher
Make sure all parts are secure
Make sure your pressurized bottle does not have
any defects.
`Plagarism
Bell Ringer



What is your total net force?
How did Newton’s 3rd law affect your rocket?
What happens to your car as a bug smashes into
your windshield?
Gravitational Force
Attractive force between all pieces of
matter

Newton’s Law of Gravitation
Every particle in the universe exerts
an attractive force on every other
particle equal to:
F=G
m1m2
r
2
Newton’s Law of Universal
Gravitation
F=G

m1m2
Where G = 6.673 x 10
Universal
r
2
-11
2
N·m /kg
2
gravitational constant
m1 and m2 are the masses of each particle
 r is the distance between the particles

Thought question.


The Physic’s diet… “You can easily loose weight
within the matter of seconds with my weight loss
program.”
How is this possible?
Newton’s Law of Universal
Gravitation
Other Useful Constants
Mass of the Earth (mE):
24
5.98x10 kg
Radius of the Earth (rE):
6
6.38x10 m
Mass of the Moon (mM):
22
7.35x10 kg
Sample Problem
What is the gravitational force
between the Earth and the Moon?
At its closest point, the Moon is only
363,104 km (225,622 miles). And at
its most distant point, the Moon gets to
a distance of 406,696 km (252,088
miles).
Weight and Mass
Weight: The gravitational force that is
exerted on an object
 Always acts directly downward

Fg = G
mE · m
Fg = m· g
rE
2
For objects “close” to
the surface
Sample Problem
What is the gravitational force
between the Earth and the Moon?
Bell Ringer


“Superman's ability to fly has been explained as a
result of Earth's gravity being much less than that
of his home world…”
Krypton, Superman’s planet of origin and about the
same size as earth, is said to have a gravitational
pull 15 times larger than Earth. If Superman’s mass
is 90.0 kg, what is the mass of Krypton?
Gravitational Force
Attractive force between all pieces of
matter

Newton’s Law of Gravitation
Every particle in the universe exerts
an attractive force on every other
particle equal to:
F=G
m1m2
r
2
Newton’s Law of Universal
Gravitation
F=G

m1m2
Where G = 6.673 x 10
Universal
r
2
-11
2
N·m /kg
2
gravitational constant
m1 and m2 are the masses of each particle
 r is the distance between the particles

Thought question.


The Physic’s diet… “You can easily loose weight
within the matter of seconds with my weight loss
program.”
How is this possible?
Bell Ringer

A 60 kg boy and 40 kg girl are
sitting 2m apart. Assuming that
the force of attraction is caused
by the universal gravitational
force, how great is the force
between them?