Transcript Inertia_in_action

Inertia in Action
Objects at rest remain at rest
and objects in motion remain in
the same kind of motion unless
acted upon by an outside force.
Inertia Summary
Objects tend to “keep on doing what they’re doing.”
Newton’s 1st Law summarized
Aristotle
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Aristotle said that objects need an applied
force in order to keep moving.
Galileo said that this was not true… that
objects will continue their motion UNLESS an
outside force was applied.
Galilee Galileo… Italian scientist
Galilee Galileo (15 February 1564[2] – 8 January 1642) was
an Italian physicist, mathematician and astronomer who
played an instrumental role in the scientific revolution of the
late middle ages.
He is often given credit for inventing the telescope, though he
actually observed some kids playing with a pair of lenses, and
adding a tube developed the concept.
With his telescope he was able to verify that Copernicus was
correct: the sun is the center of the solar system, not the
earth.
Galileo was the first scientist to calculate the rate of
acceleration due to gravity at the Leaning Tower of Pisa.
Galileo has been called the "the "father of modern science,"
and Stephen Hawking said, "Galileo, perhaps more than any
other single person, was responsible for the birth of modern
science."
Galileo
Galileo discovered that all objects fall at the same rate
Isaac Newton (Dec. 25th) 1642 - 1727
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Before Galileo, people thought that all objects tend
to come to their rest position.
They thought that a force was always needed to keep
things moving.
Newton validated Galileo mathematically.
Inertia…
Objects tend to “keep on doing what they’re doing.”
Inertia – Objects resist change…
Inertia: The resistance an object has to a
change in its state of motion.
Mass: That quantity which depends solely
upon inertia.
Inertia – What’s this?
Inertia – Time for a demo…
Explain what happened.
Anvil on the chest demonstration
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Why is the man’s chest not crushed in the demonstration?
Here is another way to demonstrate inertia of rest – driving
a nail into a block of wood on top of several very heavy
books.
Inertia – Time for another demo…
Explain why this happened.
Inertia – from a cat’s point of view
Law of Cat Inertia: A cat at rest will tend to
remain at rest, unless acted upon by some outside
force - such as the opening of a can of cat food, or a
nearby scurrying mouse.
Law of Cat Motion: A cat will move in a straight
line, unless there is a really good reason to change
direction, such as…
Inertia – skiing
When we ski we’re aware of inertia: Notice how
this skier knows he cannot change his direction of
motion without applying a force with his skis.. er…
Paws.
Inertia – rotating ball
Inertia: Ask yourself: what direction was the ball
going when the string broke?
Inertia in a bus
If you drop a ball in a bus while it is moving at 50
km/hr how fast will it be moving?
Will it land behind you, at your feet or in front of you?
Bus slowing down inertia
If a ball is laying at your feet on a bus while it is
moving at 50 km/hr how fast will it be moving?
What will happen to the ball if the bus-driver applies
the brakes?
What would an outside observer see?
Bowling inertia
The bowling ball is much heavier than the pins.
The bowling ball is moving at a constant speed.
The pins are at rest.
Describe the inertia here. (Bowling ball and the pins)
Free Fall
As demonstrated, when an object is
”falling” it can be aid to be “weightless.”
What does inertia have to do
with the following?
Inertia Quiz
In the absence of air resistance, a
bowling ball falls to the ground
_____ a feather. (Choose only one
answer)
 faster than
 slower than
 at the same rate as
 with greater velocity than
Question # 2
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Inertia is an object's resistance
to a change in _____. (Choose
only one answer)
mass
motion
weight
gravity
Question #3
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An object with a larger _____
has more inertia. (Choose only
one answer)
mass
motion
gravity
energy
Question #4
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According to Isaac Newton, an
object at rest _____ unless
acted on by another force.
(Choose only one answer)
moves
remains at rest
has momentum
contains gravity
Question #5
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Jim and Jan are arguing in the cafeteria.
Jim says that if he throws a ball with a
greater speed it will have a greater
inertia. Jan argues that inertia does not
depend upon speed, but rather upon
mass.
Who do you agree with?
Jim – speed gives the more more momentum
Jan – inertia depends only upon mass
Neither Jim nor Jan is correct
Question #6
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Supposing you were in space in a
weightless environment, would it require a
force to set an object in motion?
No – things will just coast along, without gravity
to give them a weight.
Yes – inertia depends only upon mass
Absolutely yes! Even in space objects have mass.
And if they have mass, they have inertia. That is,
an object in space resists changes in its state of
motion. A force must be applied to set a
stationary object in motion. Newton's laws apply everywhere!
Question #7
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Fred spends most Saturday
afternoons at rest on the sofa,
watching college football games and
consuming massive quantities of
food. What effect (if any) does this
practice have upon his inertia?
Explain.
Fred's inertia will increase!
Fred will increase his mass if he makes a
habit of this. And if his mass increases,
then his inertia increases.
Question #8
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Ben TooClose is being chased through the
woods by a bull moose which he was
attempting to photograph. The enormous
mass of the bull moose is extremely
intimidating. Yet, if Ben makes a zigzag
pattern through the woods, he will be able
to use the large mass of the moose to his
own advantage. Explain this in terms of
inertia and Newton's first law of motion
The large mass of the bull moose means that
the bull moose has a larger inertia. Thus, Ben
can more easily change his own state of motion
(make quick changes in direction) while the
moose has great difficulty changing its state of
motion.
Question #9
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How is inertia
demonstrated in
the picture to the
left?
Question #10
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Explain each of the above demonstrations
done in class.
Bonus
Bonus
Bonus
Other examples of inertia
Why is it that a slow pull on the roll of TP will
cause it to unwind, yet a quick jerk will rip off
One square of TP?
More examples
Why does the water not
fall out of the bucket
when whirled around
your head very fast, yet
it does when you simply
hold it over your head?
Explain in term s of
inertia.