Transcript File

Warm Up
1.
The transfer of thermal energy is called
_________________.
2.
Madison accidentally touches the stovetop while she
is cooking and burns her arm. How was thermal
energy transferred?
a. Conduction
b. convection
c. radiation
3.
A greenhouse has a glass ceiling that captures in
heat to grow plants. It receives thermal energy by
a. Conduction b. convection
c. radiation
4.
Warm air rises and cold air sinks because of
a. Conduction
b. convection
c. radiation
Newton’s Laws of Motion

Newton’s Laws of Motion
Newton’s 1st Law

An object at rest stays at rest, and
an object in motion stays in motion
at a constant speed and in a
straight line unless acted on by an
unbalanced force.
•
Friction and Newton’s First Law
Friction between an object and the
surface it is moving over is an
example of an unbalanced force that
stops motion.
Newton’s 1st Law
sometimes called the law of
inertia.
 Inertia is the tendency of all
objects to resist any change in
motion.

•
•
•
Mass is a measure of inertia.
More mass = more inertia
So, changing the motion of an object
that has a small mass is easier than
changing the motion of an object that
has a large mass.
Terry is riding her skateboard.
Suddenly one of the wheels hits a
small rock and the skateboard stops.
Terry stumbles forward off the
skateboard, and catches her balance at
the last moment before she falls to
the ground.
How does inertia affect Terry and her
skateboard?

Jack is carrying a cup of water. He
doesn’t see a wrinkle in the floor rug and
he trips. Jack manages not to fall or drop
the cup, but the water sloshes over the
side of the cup and onto the floor.

What keeps moving?

Jonathon wants to put ketchup on his
hamburger. He turns the kethcup bottle
at an angle toward his plate and smacks
the bottom of the bottle until the ketchup
comes.

How does inertia affect the ketchup in
the bottle?

The Jacksons are driving to the lake when
a car in front of theirs slams on its brakes.
Mrs. Jackson slams on her brakes, too.
Everyone is wearing their seatbelts which
stop them from being thrown forward in
the car.

How does inertia affect the people in the
Jackson car?
Newton’s Second Law
Inquiry

Drop the marble and the waded up piece of
paper at the same time, from the same height.

Now drop them into your bowl of sand.

Answer the following questions using complete
sentences. Do they fall at the same rate? Why?

Which has a greater force of impact when they
hit the ground? Why?
Newton’s

nd
2
Law
The acceleration of an object
depends on the mass of the
object and the amount of force
applied.
Force = mass x acceleration
Newton's 2nd Law
- Trains
start slow and are hard to
stop, due to their large mass.
- Motorcycles can go so fast due
to their small size and big engines.
- It takes more force
to push a loaded
shopping cart, than
an empty one.
•
Part 1: Acceleration depends on
mass.
If you push 2 objects with the same
force, the object w/ the smaller mass
will accelerate more.
•
Part 2: Acceleration depends on
force.
If two objects have the same mass, the
one you push harder (more force) will
accelerate more.

Four remote control cars with different
masses are racing toward a wall. If each
car accelerates at 10 m/s2 as it
approaches the wall, which car will hit
with the GREATEST force?

A student ran four tests to see how different
amounts of mass affect the force of a wagon rolling
down a ramp at a constant acceleration. Additional
mass was added to each wagon. Which wagon will
have the GREATEST force when it gets to the
bottom of the ramp?
Dry-Erase MC
With your table partner discuss the
answer to the following questions. Write
your answer down on the white board.
 Alternate writing for each question
 When time is called show your answer.
 Be prepared to explain.

The table shows the accelerations
produced when different forces act on a 5
kg mass. Assuming that the pattern in the
table continues, use these data to predict
what the acceleration would be when a
100 N force acts on a 5 kg mass.
A 10 m/s2
B 100 m/s2
C 20 m/s2
D 30 m/s2

2. Friction acting on a rolling ball to
eventually bring the ball to a stop is an
example of which of the following?

A an unbalanced force

B gravity

C a balanced force

D momentum

a
F
m represents
The equation
Newton’s second law of motion. Based
on this equation, if balanced forces act
on an object, which of the following
outcomes can be expected?
A The object’s acceleration will be
negative.
B The object’s acceleration will be zero.
C The object’s mass will decrease.
D The object’s mass will increase.

An object moving in a straight line with a
constant speed has no unbalanced forces
acting on it. How will the object’s motion
change over time?
A The object will gradually slow down and
come to a stop.
B Centripetal force will cause the object to go
into a circular orbit.
C The object’s motion will remain unchanged.
D The object will accelerate and change
direction.
To complete the calculations for
F = ma

◦ Determine what values you are given
◦ Plug your “known” or given values into
the equation.
◦ Solve the equation for the missing
values.

Example: a rock is thrown with a force
of 20 N and accelerates at a rate of 4
m/s2. What is the mass of the rock?
◦ Given: force = 20N
4m/s2
◦ Plug in: 20 = m4
◦ Solve:
20
4
=
acceleration =
𝑚4
4
◦ 5=m
◦ The mass of the rock is 5 kg.

Example: A boy pushes a cart with a mass
of 50 kg at a rate of 4 m/s2. What is the net
force the boy exerts on the cart?

Given: mass = 50 kg
4m/s2
acceleration =
◦ Plug in: 20 = m4
◦ Solve: f = 50 x 4
◦ F = 200
◦ The boy exerts a force of 200 N
Dry-Erase
With your table partner discuss the
answer to the following questions. Write
your answer down on the white board.
 Alternate writing for each question
 When time is called show your answer.
 Be prepared to explain.


A small satellite has a mass of 75kg and an
acceleration of 3 m/s2. What is the net
force of the satellite?

A bicycle has a mass of 10kg and an
acceleration of 2m/s. What is the net
force of the bicycle?

A car has a mass of 1000kg and an
acceleration of 2m/s2. What is the net
force of the car?

A tractor (m=200kg) backs up with an
acceleration of 3m/s2. What is the net
force of the tractor?

A large pencil is thrown across the room
with an acceleration of 10m/s2. If the
pencil has a mass of 1kg, what is the
pencil’s net force?

A person speeding up with an
acceleration of 1m/s2 has a net force of
50N. What is the mass of the person in
grams?

A bicycle has a mass of 10kg and an
acceleration of 5m/s2. What is the net
force of the bicycle?
Newton’s Laws of Motion

Newton’s Laws of Motion
NEWTON’S THIRD LAW OF
MOTION
 states
that every time one object
exerts a force on another object,
the second object exerts a force
that is equal and opposite in
direction back on the first object.
In other words…
For every action, there is an
equal and opposite reaction.
3rd Law
According to Newton,
whenever objects A and
B interact with each
other, they exert forces
upon each other. When
you sit in your chair,
your body exerts a
downward force on the
chair and the chair
exerts an upward force
on your body.
3rd Law

There are two forces
resulting from this
interaction
◦ Action forces:
◦ Reaction forces
Newton’s 3rd Law in Nature
Consider the propulsion of a
fish through the water. A fish
uses its fins to push water
backwards. In turn, the water
reacts by pushing the fish
forwards, propelling the fish
through the water.
 The size of the force on the
water equals the size of the
force on the fish; the direction
of the force on the water
(backwards) is opposite the
direction of the force on the
fish (forwards).

3rd Law
Flying gracefully
through the air, birds
depend on Newton’s
third law of motion. As
the birds push down on
the air with their wings,
the air pushes their
wings up and gives
them lift.
Consider the flying motion of birds. A bird flies
by use of its wings. The wings of a bird push air
downwards. In turn, the air reacts by pushing
the bird upwards.
 The size of the force on the air equals the size
of the force on the bird; the direction of the
force on the air (downwards) is opposite the
direction of the force on the bird (upwards).
 Action-reaction force pairs make it possible for
birds to fly.

Other examples of Newton’s Third Law

The baseball forces the
bat to the left (an
action); the bat forces
the ball to the right (the
reaction).
3rd Law

Consider the motion of
a car on the way to
school. A car is
equipped with wheels
which spin backwards.
As the wheels spin
backwards, they grip the
road and push the road
backwards.
3rd Law
The reaction of a rocket is an
application of the third law of
motion. Various fuels are
burned in the engine, producing
hot gases.
The hot gases push against the
inside tube of the rocket and
escape out the bottom of the
tube. As the gases move
downward, the rocket moves in
the opposite direction.
Momentum
A characteristic of a moving object
related to the mass and velocity of the
object
 Momentum= mass * velocity
 Unit= kilogram meters per second
 The momentum of an object is in the
same direction as its velocity.

Check for Understanding

Which has more momentum: a 3.0 kg
sledgehammer swung at 1.5 m/s or a 4.0
kg sledgehammer swung at 0.9 m/s
Law of Conservation of Momentum

The total momentum of any group of
objects remains the same, or is conserved,
unless outside forces act on the objects.