ch 4-6 notes
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Ch 4-6 Notes. Mr. Russo Beaumont High School. Objective: Ch 4.3-4.5 (Pg 40) . We will be able to define inertia and explain Newton’s first law of motion. Ch 4.3 – 4.5 Notes Force. Force – Any push or pull. Friction. - PowerPoint PPT PresentationTRANSCRIPT
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Ch 4-6 NotesMr. Russo
Beaumont High School
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Objective: Ch 4.3-4.5 (Pg 40) We will be able to define inertia and
explain Newton’s first law of motion.
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Ch 4.3 – 4.5 NotesForceForce – Any push or pull
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FrictionFriction – Name given to force that
acts between materials that touch as they move past each other
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InertiaInertia – Every material object resists
change in its state of motion (laziness of an object)
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Figure 4.3
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Newton’s 1st lawNewton’s 1st Law (Law of inertia) –
Every object continues in a state of rest or of motion in a straight line at constant speed, unless it is compelled to change that state by forces acting upon it. – Newton
An object at rest stays at rest, and an object in motion stays in motion without forces acting upon them
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This reminds me of youStudents doing math 2 and 3 step math
problems
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DemosHanging Mass
Penny in a cup
Paper and bottle
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Why do objects slow down and stop?Because of outside forces, mostly
because of friction
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What would happen if you threw an object from a space station?It would go forever
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Inertia ExplainedThe more mass an object has, the more
inertia it has. Less mass, less inertia
Is it easier to pick up a toy car or a real car?
Inertia is laziness
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What is mass?Mass – The amount of material present
in an objectMeasure of inertia of an objectMASS DOESN’T CHANGE
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What do we measure mass in?Mass is measured in kilograms
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What is the difference between mass, volume and weight?
Mass Volume WeightMeasure of how much
matter present (How much inertia)
How much space it is taking up.
Force of gravity on an
object.(Depends on
location)To calculate weight we use the formulaw = m*g
g = force of gravity
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For ExampleMass of boulder = 10
kgWeight of boulder = 0
kgVolume of boulder =
10 L
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On your white boardIf a woman has a mass of 50 kg,
calculate her weight in Newtons
w = mgw = (50kg)(9.8m/s2)w = 490 N
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On your white boardCalculate in newtons the weight of a
2000 kg elephant
w = mgw = (2000kg)(9.8m/s2)w = 19,600 N
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On your white boardCalculate in newtons the weight of a 2.5
kg melon. What is the weight in pounds? (4.45 N = 1lb)
w = mgw = (2.5kg)(9.8m/s2)w = 24.5 N24.5 N / 4.45 N = 5.5 lbs
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On your white boardAn apple weighs about 1 N. What is its
mass in kilograms? What is its weight in pounds? (2.2 lbs = 1 kg)
w = mg1 N = (m)(9.8m/s2)m = 1N / 9.8 m/s2 = .1 kg.1 kg = .22 lbs
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On your white boardSusie finds she weighs 300 N.
Calculate her mass.
w = mg300 N = (m)(9.8m/s2)m = 30.6 kg
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Objective: Ch 4.6-4.9 (Pg 44)Given 2 or more forces we will be able
to calculate the net force exerted on an object
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Notes 4.6 – 4.9, Force Net Force – The
combination of all forces acting on an object.Net force
changes an objects state of motion
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What happens if you pull with equal and opposite forces?Nothing! If forces are equal and opposite the net
force is zero!
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What is the minimum # of forces acting on an object at rest?2Force of gravity (Down)Normal Force (Up)
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Normal ForceNormal Force – Upward force on an
objectalso called the support force
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EquilibriumEquilibrium – When all forces on an
object cancel out. Net force is zeroObject will not move if at rest
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Draw Figure 4.11
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Tension ForceTension Force – When atoms are
stretched (As opposed to being compressed)
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When the angle from vertical increases, what happens to the tension force?Tension always increases as the angle
away from vertical increases
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Slogan:Net Force is zero, of course – TannerDo you move – JoseNet Force Zero, no excuses – MiaEquilibrium equals net force zero – MichaelAre you in motion – TimChuck Norris & Mr Russo, Net force ZERO!
– JJNet Force is zero, unless your Chuck Norris
- Chris
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What happens if you flip a coin in an airplane while its moving?It behaves as if the plane were at rest.
Why?
Inertia
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Objective
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Ch 5.1-5.4 - What must happen for acceleration to occur?Forces cause acceleration
Hockey Puck at restNo Acceleration
Player hits puck Acceleration
Puck moving across iceNo acceleration
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Acceleration is directly proportional to what?Acceleration is directly proportional to
the Net Force acting on it
More force = more acceleration
Less force = less acceleration
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Newton’s 2nd LawNewton’s 2nd Law – The acceleration produced by
a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force and is inversely proportional to the mass of the object. – Newton
More Force = More acceleration (Directly Related)
More Mass = Less Acceleration (Inversely Related)
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What is the formula for acceleration?Acceleration = Net force / Mass
More commonly
F = ma
a = F/m
m = F/a
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What are the units for the NewtonForce is measured in NEWTONS
Force is mass x acceleration
Units are kg*(m/s2)
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FrictionFriction – between two objects
touching.
Always acts in direction opposite to state of motion
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FluidsFluids – Gases
or liquids ( because they
flow)
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Air ResistanceAir Resistance – Friction acting on
something moving through air
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How can acceleration be zero when there is still a force applied?When there is a force applied, the force
of friction will balance it out and make net force zero
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PressurePressure - force per unit area
P= F/A
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Terminal Speed / Terminal VelocityTerminal Speed -
Object is falling and no longer is accelerating
Terminal Velocity – Same thing, direction is down
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Ch 6.1-6.6 If you push against a wall, how come it doesn’t fall over?Because the wall is pushing back on
you.
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InteractionInteraction – A mutual action between
objects where each object exerts equal and opposite forces
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Newton’s 3rd LawNewton’s 3rd Law – Whenever one
object exerts a force on a 2nd object, the second object exerts an equal and opposite force on the 1st object.
In other words – For every action there is an equal and opposite reaction
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Action / Reaction ForceAction /Reaction Forces – Co-parts of a
single interaction. One cannot exist without the other.
No such thing as a single force
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ExampleAction: Earth’s gravity pulls down a
boulder
Reaction: The boulders gravity pulls up on the Earth
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ExampleAction: Rocket pushes gas
Reaction: Gas pushes rocket
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What pushes a car as you drive?Action: Tire pushes against the road
Reaction: Road pushes against tire
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Figure 6.7
H0w come the cannon doesn’t move just as fast backwards as the cannon ball goes forward?
A smaller mass has greater accelerationA greater mass has less acceleration
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ExampleHow come the Earth doesn’t move just
as fast up as the boulder goes down?
Larger masses have lessacceleration
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Figure 6.8How does a rocket
accelerate?
Action Force: Rocket pushes air molecules down
Reaction Force: Air molecules pushing rocket up
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Figure 6.13 – Horse and the CartHow come if forces are
equal and opposite, the cart still moves?
The friction between the horse and the ground is greater than the cart wheels and the ground
F - f