Transcript File - Mrs. Phillips` Physical Science Webpage

http://www.youtube.com/watch?v=YdjN7
dIXRXo&feature=youtube_gdata_player
Crash Test Dummy 2
Newton’s 1st Law of Motion

Objects in motion tend to stay in motion at
constant velocity, and objects at rest tend to
stay at rest, unless acted upon by an outside
force.

The outside force that stops objects that are rolling
along is friction. Without friction, the object wouldn’t
stop until another force acted upon it.

http://nbclearn.com/nfl
Inertia!

http://www.youtube.c
om/watch?v=vfnt8Sd
j7cs
Newton’s 1st Law of Motion

Inertia is the property of matter that resists any change in
motion.




Standing on a bus: When it starts moving, you lose your balance, when
it stops you fall forward.
When driving in a car, if the road curves, the driver must turn the
steering wheel so that the car will follow the curve; the people inside
continue to move straight ahead until the seat or walls of the car force
them to follow the curve.
You are sitting still at a red light and another car hits you from behind.
How does a headrest help in this instance?
Ex: Tie a string to a small boat and you can pull it – why can’t
you pull an ocean liner the same way?


Both boat and ocean liner are ‘weightless’ as the water is supporting their
weight so you don’t have to.
The ocean liner has more mass, so it has more inertia.
http://youtu.be/oKb2tCtpvNU
http://www.youtube.com/
watch?v=uiyMuHuCFo4
Slinky

How does changing mass affect the
acceleration?

How does changing the force you use,
affect acceleration?
http://youtu.be/sKSPxQjPOm0
Newton’s 2nd Law of Motion

The 2nd law says that the acceleration of an
object depends on the object’s mass and the
size of the force acting on it.

The formula that explains Newton’s 2nd Law of
Motion is
Force = mass x acceleration (F = ma)
 OR…… a = F/m

 This
formula shows you why a boulder and a pebble
would fall at the same rate!
Newton’s 2nd Law of Motion

1st law shows you that acceleration and force are
related - the 2nd law explains how they are related.
http://nbclearn.com/nfl
 Stronger forces increase acceleration;



Kicking an object will cause greater acceleration than flicking it with a
finger
Larger masses require more force for acceleration

Requires more force to move a truck than it does a car

So, a 750 kg car gets better gas mileage than a 2000 kg truck, at the
same acceleration because it takes less force to get it going.

A semi has greater _____. It requires a greater _____ to achieve the
same ______ (make it around the corner). What supplies that _____?
Problems
A weightlifter raises a 200 kg barbell with an acceleration of 3
m/s2. How much force does the weightlifter use to lift the barbell?
Step 1:
Write Knowns
Step 2:
Write Formula
Step 3:
Plug Knowns into
Formula
Step 4:
Solve – ensure
units carry through
Problems
1. How much force is needed to accelerate a 1000 kg car at a
rate of 3 m/s2?
2. If a 70 kg swimmer pushes off a pool wall with a force of 250N,
at what rate will the swimmer accelerate away from the wall?
3. A dancer lifts his partner above his head with an acceleration
of 2.5 m/s2. The dancer exerts a force of 200N. What is the
mass of the partner?
Newton’s 2nd Law Recap

You are riding your bike, pulling a loaded
wagon behind you. The wagon suddenly
becomes unhitched.

Give one of the two ways you would know this without
looking.

Why is it so Hard to Go into Space?
https://vimeo.com/86572593

http://nbclearn.com/nfl
3rd
Law
Newton’s 3rd Law of Motion

3rd Law: For every
action there is an equal
and opposite reaction;
All forces come in pairs
Push on a wall, it pushes
back
 Airplanes push air out of
the engines, the air
pushes the plane forward

Newton’s 3rd Law of Motion

Since they act in opposite directions, do they cancel each
other out? Why or why not?
cuz
they are not acting on the SAME object!
Ex: In a stalemated tug-of-war both sides are pulling on the same rope so ARE
NOT A-R pairs
One team pulls on the rope, the rope pulls back IS an A-R pair
http://ed.ted.com/lessons/joshua-manleynewton-s-3-laws-with-a-bicycle
Now Explain THIS!
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ook&utm_source=io9_facebook&utm_medium=so
cialflow
Newton’s Laws of Motion

Explain the launch of
the space shuttle using
all three Laws of
Motion…….
Momentum




All moving objects have momentum.
Momentum is determined by the mass of the object and
the velocity at which it is traveling.
Momentum = mass x velocity
Can an object with less mass have more momentum than a
larger one?


A 75 kg fullback running downfield and collides with a 125 kg
defensive back blocking him, and runs him down. - Why?
Is momentum a vector?
Momentum

The law of conservation of momentum,
states that the total momentum of any group
of objects remains the same unless an
outside force acts on the objects.

Ex: Billiards - what is the outside object?
 Once
the pool balls start moving, why don’t they just keep
moving forever, transferring momentum back and forth to
each other?

Fireworks……
Momentum

The total momentum of objects that
interact must be the same after the
interaction as the total momentum
before to the interaction.
 If
one of the objects in a collision speeds
up, then the other must slow down. –
billiards….explain.
Momentum

If the system was at rest to begin with (0
momentum), then the momentum of one
object moving forward must equal the
momentum of the other object moving
backward.
 Shotgun vs bullet
Momentum

If two skaters are at rest, and one
pushes off of the other and slides
away at 35 m/s, and the other
slides away in the opposite
direction at 28 m/s, what is the total
momentum of the two skaters?
Practice

What is the momentum of a 920 kg car moving at a
speed of 25 m/s?

Which has more momentum, a 250kg dolphin
swimming at 4 m/s or a 350 kg manatee swimming at
2 m/s?

Find the force it would take to accelerate an 800 kg
car at a rate of 5 m/s2.

What is the acceleration of a 0.15 kg hockey puck
struck with a force of 1.8 N?
Impulse

Impulse changes motion.

To change an object’s motion, you need a
push or pull ….. Force
 http://www.youtube.com/watch?v=rXGKys62TXw&f
eature=related
 http://www.youtube.com/watch?v=xG9dAROIKPQ

But the amount of time you apply that force
affects the motion as well
 Toss
an egg at a wall = splat
 Toss an egg into a blanket with give =
 Both stop the egg, the blanket extends the time the
force is applied
Impulse

Impulse = F (t)

The greater the impulse, the greater the change in
motion
 Hand
gun vs shotgun
 Longer cannon
 Follow through on swing in baseball or golf vs bunt/putt
 Car crash
 Jumping from a height – straight legged vs bending legs
when land
 Quick jab in boxing
Impulse

Impulse is greater when objects bounce.

It takes more impulse to stop an object and
throw it back than it does to just stop it
 Weight
ball
 Water wheel during the gold rush – flat paddle vs ushaped

The u-shape caused the water to hit and do a u-turn or
bounce back making the paddles much more effective
 Sky
diving