Transcript Early Work – Mar. 26

Early Work – Mar. 26
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List five forces you encountered during
break.
Foldables
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Create the foldable on the front page of
ch. 4
Read section 1
 P103: 1 - 7
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Early Work – Mar. 28
If an object of mass 3 kg has an
acceleration of 5 m/s2, what force is
acting on it?
 Write the three forms of the equation for
Newton’s Second Law.
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To Get Done (10 minutes)
Some of you haven’t finished your ch. 3
tests!!
 Homework – if done show teacher and
then put in InBox
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Activity
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On a blank sheet of paper,
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What is inertia?
How are inertia and Newton’s First Law related?
If an object has a mass of 40 kg and a force of 10
N acts on it, what will the object’s acceleration be?
If an object has a mass of 10 kg and is being
accelerated at the rate of 1.5 m/s2, what force is
acting on it?
If a 25 N force accelerates an object at 12 m/s2,
what is the mass of the object?
Activity Cont’d
Draw a picture of the apparatus.
 Predict what you think will occur when
the pie tin is hit with a broom.
 What occurred?
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4.2 - Gravity
Early Work – Mar. 30
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What are the two types of friction we
discussed?
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Define inertia.
Gravity
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An attractive force between any two
objects that depends on the masses of
the objects and the distance between
them
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Earth is the only thing close enough and
large enough to us to feel it’s gravitational
attraction
Universal Gravitation
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Law that enables us to calculate the
gravitational attraction between any two
objects
m1m2
F =G 2
d
Earth’s Gravity
Earth attracts everything at the same
rate (or pulls it with the same
acceleration)
 Earth’s gravity accelerates objects at
9.8 m/s2
 When in free fall (like from being
dropped), the force on an object can be
calculated by F = ma or F = mg.
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Weight
Even when not in free fall, Earth still has
it’s pull on you. It causes you to be
exerting a force on what you are sitting
or standing on.
 That force is called weight.
 W = mg
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Weight v. Mass
Weight is a force (measured in N)
 Mass is the measure of the amount of
matter present (measured in kg or g)
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Let’s weigh ourselves
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Use table on page 107
Projectiles
Projectile – anything thrown or launched
 Earth’s gravity causes projectiles to arc
downward
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Centripetal Force
Centripetal Acceleration – acceleration
toward the center of a curved or circular
path
 Centripetal Force – the force exerted
towards the center of the path
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Hmwk
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P111 – 1 – 3, 6
Early Work – Apr. 3
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If every object has its own gravity, why is
it that we are not attracted (literally) to
each other?
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Have homework out and ready to grade
Worksheet
Complete p20
 Complete sections 1 and 2 on p19
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Newton’s Third Law
Action-reaction pairs
 To every action force there is an equal
and opposite reaction force
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• When you jump on a trampoline, for
example, you exert a downward force on
the trampoline.
• Simultaneously, the trampoline exerts an
equal force upward, sending you high into
the air.
Rocket Propulsion
• In a rocket engine, burning fuel
produces hot gases. The rocket
engine exerts a force on these
gases and causes them to
escape out the back of the
rocket.
• By Newton’s third law, the
gases exert a force on the
rocket and push it forward.
Momentum
• A moving object has a property called
momentum that is related to how much
force is needed to change its motion.
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The momentum of an object is the
product of its mass and velocity.
Conservation of Momentum