Transcript What did the boy cat say to the girl cat on

HAPPY VALENTINE’S DAY!
Please get your folders.
Copy down tonight’s homework.
Have last night’s homework on your
desk (conclusions for Part 2 of
Shipping and Sliding; graph do-over)
Today, we will:
Talk about Newton’s other two laws
1. What did the boy cat say to the girl cat
on Valentine’s Day?
2. What did the boy octopus say to the girl
octopus?
3. What did the boy light bulb say to the
girl light bulb?
4. What did the paper clip say to the
magnet?
5. What do you call a very small
valentine?
Tomorrow’s quiz
motion graphs
definition of force
Newton’s three laws of motion
Objects accelerate in the direction of
the net force applied to objects.
FORCE = MASS ● ACCELERATION
acceleration = force
mass
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To a scientist, acceleration is any change in
velocity.
OK, so remind me: What is VELOCITY???
Velocity is speed in a given direction.
So, how can velocity change???
The object can SPEED UP.
The object can SLOW DOWN.
The object can CHANGE DIRECTION.
A dog chasing
its tail is
accelerating –
WHY?
The only way to NOT accelerate is
to...
Travel in a straight line
at constant speed.
(all lines are straight)
acceleration = force
mass
•The SI unit for force is the Newton.
•Let’s say a 4N force acts on a 2kg
mass.
What is the acceleration?
•What if we increase the force to 8N?
•What if we increase the mass to 4kg?
LET’S GO SHOPPING!
acceleration = force
mass
•The more force that is applied, the more
the object will accelerate
•(putter vs. feather)
•The greater the mass of the object, the less
it will be accelerated by a given force
•(golf ball vs. ping pong ball)
WHAT THIS MEANS:
1. To get something to accelerate more (speed up
quickly, slow down quickly, change direction
quickly), you must apply more force.
Example: slamming on the brakes to stop
quickly
WHAT THIS MEANS:
2. It takes more force to accelerate a bigger thing
than a smaller thing.
 For
every action force,
there is an equal and
opposite reaction force.
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.
There are two forces
resulting from this
interaction – the
force you exert on
the chair and the
force the chair exerts
on your body. These
two forces are called
action and reaction
forces.
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This means that when I am
pushing on the wall,
 THE
WALL IS PUSHING
BACK ON ME!!!
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Action-reaction force pairs make it possible for
objects to move.
What is the direction of your force when you
are walking forward?
What is the direction of your force when you
jump on a trampoline?
 Think
about the
direction of
the force
you apply
when you
row a boat:
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Think
about the
direction
of the force
you apply
when you
shoot an
arrow.
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The bat and ball
each put a force on
each other – each
also experiences a
reaction force.
This sends the ball
back out toward the
field and sends the
bat backward
(recoil).
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.
How do you get something to accelerate a
lot?
Give an example of an action/reaction force
pair in this classroom.
How does the Coke/Mentos car illustrate
the 1st Law? 2nd Law? 3rd Law?