Transcript Unit 2 - Angelfire

Motion
Aristotle

4 elements that are the building blocks of the
world around us: _______________,
_______________, _______________,
_______________


Rock – belongs to the earth element, would fall
back to the earth
Smoke – belongs to the fire element, rises above
air
Aristotle

_______________ Motion – straight up
and straight down motion


Circular motion is the natural motion of the
heavens – all the planets revolve around the earth
_______________ Motion – result of
forces that pushed or pulled – from some
external cause

Cart being pulled by a horse
Copernicus




Studied the planets
Earth and the other planets move around the
sun.
Worked on this idea in secret to escape
persecution.
The day he died, he received his work in print
(1543)
Galileo

Expanded on Copernicus’ ideas

Brought in the concept of ______________

Time for the motion to happen


A study of motion will involve the introduction
of a variety of quantities which are used to
describe the physical world.
Examples of such quantities include distance,
displacement, speed, velocity, acceleration,
force, mass, momentum, energy, work,
power, etc.

All these quantities can by divided into two
categories:
 _______________


A vector quantity is a quantity which is fully described
by both magnitude and direction.
_______________

A scalar quantity is a quantity which is fully described
by its magnitude.
Vector Quantities
_______________
 _______________
 _______________
 _______________

Linear Motion


Motion in a straight line
_______________ – measure of how fast
something is moving


mph
_______________ – speed in a given
direction


m/s northward
_______________ – the rate at which
velocity is changing


m/s2
Can be positive or negative
Projectile Motion

The most common example of an object
which is moving in two-dimensions is a
_______________.

A projectile is an object upon which the only
force acting is _______________.

A projectile is any object which once
projected _______________ in motion by
its own inertia and is influenced only by the
downward force of gravity.



an object dropped from rest is a projectile
(provided that the influence of air resistance is
negligible)
an object which is thrown vertically upwards is
also a projectile (provided that the influence of air
resistance is negligible)
an object is which thrown upwards at an angle is
also a projectile (provided that the influence of air
resistance is negligible).
Horizontally Launched
Projectiles

Imagine a cannonball being launched from a
cannon atop of a very high cliff. Imagine as
well that the cannonball does not encounter a
significant amount of air resistance. What will
be the path of the cannonball and how can
the motion of the cannonball be described?

The animation below depicts such a
situation. The path of the cannonball is
shown; additionally, the horizontal and
vertical velocity components are
represented by arrows in the animation.


As the cannonball falls, it undergoes a
downward acceleration. A downwardlymoving cannonball which is gaining speed
is said to have a downward acceleration.
This downward acceleration is attributed to
the downward force of gravity which acts
upon the ball.
Acceleration Due to Gravity

Galileo – objects fall at the same rate



Did recognize that a compact object does fall
faster than a less compact object (flat paper vs.
crumpled paper)
Acceleration due to gravity (g) = 9.8 m/s2
Objects fall with the same _______________
but it will be dependent on _______________

1971, David Scott, US Astronaut, dropped a hammer
and a feather on the moon and they hit the surface of
the moon at the same time
Newton’s First Law of Motion


an object in motion continues in motion with
the same speed and in the same direction
unless acted upon by an unbalanced force.
It is the natural tendency of objects to keep
on doing what they're doing.



All objects _______________ in their state
of motion.
In the absence of an unbalanced force, an
object in motion will maintain this state of
motion. This is often called the
_______________.
Inertia is the _______________ an
object has to a change in its state of
motion. Inertia is dependent only on
_______________.




At the time, Newton's concept of inertia was in
direct opposition to the more popular
conceptions about motion.
The dominant thought prior to Newton's day was
that it was the natural tendency of objects to
come to rest.
Moving objects, or so it was believed, would
eventually stop moving since a force was
necessary to keep an object moving.
If left to itself, a moving object would eventually
come to rest and an object at rest would stay at
rest; thus, the idea which dominated the thinking
for nearly 2000 years prior to Newton was that it
was the natural tendency of all objects to
assume a rest position.



Newton's first law of motion declares that a
_______________ is not needed to keep an
object in motion.
Slide a book across a table and watch it slide to a
stop.
The book in motion on the table top does not come
to rest because of the absence of a force; rather it is
the presence of a force – the force of
_______________ – which brings the book to a
halt.


The law of inertia is most commonly
experienced when riding in cars and trucks.
In fact, the tendency of moving objects to
continue in motion is a common cause of a
variety of transportation accidents - of both
small and large magnitudes.



Consider for instance the unfortunate
collision of a car with a wall.
Upon contact with the wall, an unbalanced
force acts upon the car to abruptly
decelerate it to rest.
Any passengers in the car will also be
decelerated to rest if they are strapped to
the car by seat belts. Being strapped
tightly to the car, the passengers share
the same state of motion as the car.

As the car accelerates, the passengers
accelerate with it; as the car decelerates, the
passengers decelerate with it; and as the car
maintains a constant speed, the passengers
maintain a constant speed as well.

But what would happen if the passengers
were not wearing the seat belt? What motion
would the passengers undergo if they failed
to use their seat belts and the car were
brought to a sudden and abrupt halt by a
collision with a wall?

Were this scenario to occur, the passengers
would no longer share the same state of motion
as the car. The presence of the strap assures
that the forces necessary for accelerated and
decelerated motion exist. Yet, once the strap is
no longer present to do its job, the passengers
are more likely to maintain its state of motion.

If the car were to abruptly stop and the seat
belts were not being worn, then the
passengers in motion would continue in
motion. Assuming a negligible amount of
friction between the passengers and the seats,
the passengers would likely be propelled from
the car and be hurled into the air. Once they
leave the car, the passengers becomes
projectiles and continue in projectile-like
motion.

But why then are motorcycles not
equipped with safety harnesses? Is this
a gross oversight made by motorcycle
manufacturers?
There are many more applications
of Newton's first law of motion.


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blood rushes from your head to your feet when riding on a
descending elevator which suddenly stops.
the head of a hammer can be tightened onto the wooden handle
by banging the bottom of the handle against a hard surface.
a brick is painlessly broken over the hand of a physics teacher by
slamming the brick with a hammer. (CAUTION: Do not attempt
this at home!)
to dislodge ketchup from the bottom of a ketchup bottle, the
bottle is often turned upside down, thrust downward at a high
speed and then abruptly halted.
headrests are placed in cars to prevent whiplash injuries during
rear-end collisions.
while riding a skateboard (or wagon or bicycle), you fly forward
off the board when hitting a curb, a rock or another object which
abruptly halts the motion of the skateboard.

1. Imagine a place in the cosmos far from all
gravitational and frictional influences. Suppose an
astronaut in that place throws a rock. The rock will:

2. Mac and Tosh are arguing in the cafeteria. Mac
says that if he throws his jello with a greater speed
it will have a greater inertia. Tosh argues that
inertia does not depend upon speed, but rather
upon mass. With whom do you agree? Why?

3. If you were in a weightless environment in
space, would it require a force to set an object in
motion?

4. Mr. Wegley spends most Sunday afternoons at
rest on the sofa, watching pro football games and
consuming large quantities of food. What effect
(if any) does this practice have upon his inertia?
Explain.

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.
Newton’s Second Law of
Motion

Objects at _______________ (the condition in
which all forces balance) will not accelerate.

According to Newton, an object will only accelerate if
there is a net or unbalanced force acting upon it.

Newton's second law of motion pertains to the
behavior of objects for which all existing forces are
not balanced.

The second law states that the acceleration
of an object is dependent upon two variables
– the net force acting upon the object and the
mass of the object.

As the net force increases, so will the object's
acceleration. However, as the mass of the
object increases, its acceleration will
decrease.
Fnet = ma
1 Newton = amount of force needed to move a
1 kg object 1 m/s2
Misconception of Motion

The idea that sustaining motion requires a
continued force.
Newton’s Third Law of Motion

"For every action, there is an equal and
opposite reaction."



The statement means that in every
interaction, there is a pair of forces acting on
the two interacting objects.
The size of the force on the first object equals
the size of the force on the second object.
The direction of the force on the first object is
opposite to the direction of the force on the
second object. _______________ always
come in pairs – equal and opposite actionreaction force pairs.

While driving, Anna Litical observed a bug
striking the windshield of her car. Obviously, a
case of Newton's third law of motion. The bug
hit the windshield and the windshield hit the
bug. Which of the two forces is greater: the
force on the bug or the force on the
windshield?

2. Rockets are unable to accelerate in space
because ...
a. there is no air in space for the rockets to
push off of.
b. there is no gravity is in space.
c. there is no air resistance in space.
d. ... nonsense! Rockets do accelerate in
space.
Momentum

_______________ in motion

Mass x Velocity

The greater the _______________ acting on an
object, the greater the change in the velocity, and
the greater the change in momentum.

The more _______________ which an object
has, the harder that it is to stop.

From the definition of momentum, it becomes
obvious that an object has a large momentum if
either its mass or its velocity is large.



Consider a Mack truck and a roller skate moving down the
street at the same speed. The considerably greater mass
of the Mack truck gives it a considerably greater
momentum.
Yet if the Mack truck were at rest, then the momentum of
the least massive roller skate would be the greatest; for the
momentum of any object which is at rest is 0.
Objects at rest do not have momentum - they do not have
any "mass in motion."
Collisions

The physics of _______________ are
governed by the laws of momentum and
Newton’s Laws.

In a collision, an object experiences a force
for a specific amount of time which results in
a change in momentum (the object's mass
either speeds up or slows down).

In a collision, objects experience an
_______________; the impulse causes
(and is equal to) the change in momentum.
 _______________ = force x time (greater the
impulse, the greater the change in momentum)



Observe that the _______________ the time
over which the collision occurs, the
_______________ the force acting upon the
object.
To minimize the effect of the force on an object
involved in a collision, the time must be
_______________;
To maximize the effect of the force on an object
involved in a collision, the time must be
_______________.
Airbags in a Vehicle



Air bags are used in automobiles because
they are able to minimize the effect of the
force on an object involved in a collision.
Air bags accomplish this by extending the
time required to stop the momentum of the
driver and passenger.
The same principle explains why dashboards
are padded.

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


When encountering a car collision, the driver and
passenger tend to keep moving in accord with
Newton's first law.
Their motion carries them towards a windshield
which results in a large force exerted over a
short time in order to stop their momentum.
If instead of hitting the windshield, the driver and
passenger hit an air bag, then the time duration
of the impact is increased.
When hitting an object with some give such as
an air bag, the time duration might be increased
by a factor of 100.
Increasing the time by a factor of 100 will result
in a decrease in force by a factor of 100.

This same principle of padding a potential
impact area can be observed in gymnasiums
(underneath the basketball hoops), in polevaulting pits, in baseball gloves and goalie
mitts, on the fist of a boxer, inside the helmet
of a football player, and on gymnastic mats.
Effects of Rebounding



Occasionally when objects collide, they
bounce off each other (as opposed to sticking
to each other and traveling with the same
speed after the collision).
Bouncing off each other is known as
_______________.
Rebounding involves a change in direction of
an object; the before- and after-collision
direction is different.


The importance of rebounding is critical to the
outcome of automobile accidents.
In an automobile accident, two cars can
either collide and bounce off each other or
collide and crumple together and travel
together with the same speed after the
collision.

But which would be more damaging to the
occupants of the automobiles - the
rebounding of the cars or the crumpling up of
the cars?

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
Contrary to popular opinion, the crumpling up
of cars is the safest type of automobile
collision.
If cars rebound upon collision, the momentum
change will be larger and so will the impulse.
A greater impulse will typically be associated
with a bigger force.
Occupants of automobiles would certainly
prefer small forces upon their bodies during
collisions.


In fact, automobile designers and safety
engineers have found ways to reduce the
harm done to occupants of automobiles by
designing cars which crumple upon impact.
Automobiles are made with
_______________.


Crumple zones are sections in cars which are
designed to crumple up when the car encounters
a collision.
Crumple zones minimize the effect of the force in
an automobile collision in two ways.


By crumpling, the car is less likely to rebound
upon impact, thus minimizing the
_______________ change and the
_______________.
Finally, the crumpling of the car lengthens the
_______________ over which the car's
momentum is changed; by increasing the
time of the collision, the force of the collision
is greatly reduced.

1. Explain why it is difficult for a firefighter to
hold a hose which ejects large amounts of
high-speed water.

Would you care to fire a rifle that has a bullet
ten times as massive as the rifle?
No Seatbelt

Cars are designed with
crumple zones so they may
slow down over a longer period
of time, which keeps the force
smaller. The crumple zone
only slows the car more
gradually. The only way it
slows the occupants more
gradually is if they are attached
to the car. Stopping in a small
amount of time means the
force must be very large. This
video clip shows some very
dramatic scenes of car crash
tests with test dummies who
are not wearing seat
belts. Specifically look for cars
crumpling and people stopping
in very small amounts of time.
With Seatbelt

Seatbelts use two main
ideas to protect passengers
during a car
accident. First, they slow
the passenger down more
slowly than the passenger
running into steering wheel
or dashboard. This keeps
the force required to stop
them smaller. It also
prevents the person from
contacting any of the glass
windows in the car or
continuing on to be stopped
abruptly by the road, tree,
or another automobile. The
video clip shows the role of
the seatbelt during an
accident

This clip clearly gives the
driver a good reason to
make sure occupants in the
rear of the car are wearing
their seat belts. Not
wearing a seatbelt not only
puts your life in danger but
also anyone else who
happens to be riding with
you. The force from the
seatbelt safely decelerates
the driver, but the child in
the back seat follows
Newton's Law of Inertia and
continues moving in the
absence of a net force. The
60mph "kid" not only breaks
its own neck but also the
neck of the driver.

In this clip, we see that seat
belts and child seats not
only protect you in a frontal
impact, they could also
prevent a tragedy in rear
end collision. In this clip,
the station wagon literally
gets accelerated out from
under the "kids" sitting in
the back. They were at rest
originally, and in the
absence of a net force (from
the seat belt) they remained
at rest while the car they
were in was accelerated by
the net force from the car
that hit them. Newton's first
law can be a killer!
Energy

What is energy?




The capacity to do _______________ or
supply _______________.
Energy is weightless, odorless, and tasteless.
Energy is detected only because of its effects.
Heat is _______________ that transfers
between objects across a temperature change.

Heat cannot be detected by the sense or by
instruments – only changes caused by heat can be
detected.
Potential Energy

An object can store energy as the result of
its position.

This stored energy of position is referred to
as potential energy.

_______________ energy is the energy
which an object has stored due to its
position relative to some zero position.
Kinetic Energy

_______________ energy is the energy of
motion.

An object which has motion - whether it be vertical
or horizontal motion - has kinetic energy.

Standard metric unit of measurement for kinetic
energy is the Joule.

1 Joule is equivalent to 1 kg  (m/s2).

The amount of kinetic energy which an object
has depends upon two variables:
 the _______________ (m) of the object
 the _______________ (v) of the object.
Sound Waves
Transverse Wave

A _______________ wave is a wave in
which particles of the medium move in a
direction perpendicular to the direction which
the wave moves.
Longitudinal Wave

A _______________ wave is a wave in
which particles of the medium move in a
direction parallel to the direction which the
wave moves.
Comparison of the Two
Surface Wave

A _______________ wave is a wave in
which particles of the medium undergo a
circular motion. Surface waves are neither
longitudinal nor transverse.

Waves which travel along the surface of the
oceans.

Another way to categorize waves is on the
basis of the ability (or nonability) to transmit
_______________ through a
_______________(i.e., empty space).

Categorizing waves on this basis leads to two
notable categories:


electromagnetic waves
mechanical waves.
Electromagnetic Waves

An _______________ wave is a wave which is
capable of transmitting its energy through a vacuum
(i.e., empty space).

Electromagnetic waves are produced by the
vibration of electrons within atoms on the Sun's
surface.

These waves subsequently travel through the
vacuum of outer space, subsequently reaching
Earth.

All _______________ waves are examples
of electromagnetic waves.
Mechanical Waves

A _______________ wave is a wave which is not
capable of transmitting its energy through a vacuum.

Mechanical waves require a _______________
in order to transport their energy from one location
to another.

A sound wave is an example of a mechanical wave.
Sound waves are incapable of traveling through a
vacuum.

Slinky waves, water waves, stadium waves,
and telephone chord waves are other
examples of mechanical waves; each
requires some medium in order to exist.



A slinky wave requires the coils of the slinky;
a water wave requires water; a stadium wave
requires fans in a stadium;
and a telephone chord wave requires a telephone
chord.

_______________ is a wave which is
created by vibrating objects and passed
through a medium from one location to
another.

The medium is simply the material through which
the disturbance is moving; it can be thought of as
a series of interacting particles.

A sound wave is similar in nature to a slinky
wave.


There is a medium which carries the disturbance
from one location to another.
Typically, this medium is air; though it could be
any material such as water or steel.

Regardless of what vibrating object is creating
the sound wave, the particles of the medium
through which the sound moves is vibrating in a
back and forth motion at a given
_______________.

The frequency of a wave refers to how often the
particles of the medium _______________
when a wave passes through the medium.

The frequency of a wave is measured as the
number of complete back-and-forth vibrations
of a particle of the medium per unit of time.

A commonly used unit for frequency is the
_______________ (abbrviated Hz), where

1 Hertz = 1 vibration/second

As a sound wave moves through a medium,
each particle of the medium vibrates at the
same frequency.

The human ear is capable of detecting
sound waves with a wide range of
frequencies, ranging between
approximately 20 Hz to 20 000 Hz.

Any sound with a frequency below the
audible range of hearing (less than 20
Hz) is known as an _______________
and any sound with a frequency above
the audible range of hearing (more than
20 000 Hz) is known as an
_______________.

Dogs can detect frequencies as low as
approximately 50 Hz and as high as 45
000 Hz.

Cats can detect frequencies as low as
approximately 45 Hz and as high as 85
000 Hz.

Bats, who are essentially blind and must
rely on sound _______________ for
navigation and hunting, can detect
frequecies as high as 120 000 Hz.

Dolphins can detect frequencies as high
as 200 000 Hz.

While dogs, cats, bats, and dolphins have
an unusual ability to detect ultrasound, an
elephant possesses the unusual ability to
detect infrasound, having an audible
range from approximately 5 Hz to
approxmately 10 000 Hz.

The sensations of these frequencies are
commonly referred to as the
______________________________.

A high pitch sound corresponds to a high
frequency and a low pitch sound corresponds to a
low frequency.

The faintest sound which the human ear can
detect is known as the _______________
_______________.

The most intense sound which the ear can
safely detect without suffering any physical
damage is more than one billion times more
intense than the threshold of hearing.

Since the range of intensities which the
human ear can detect is so large, the
scale which is frequently used by
physicists to measure intensity is a scale
based on multiples of 10.

The scale for measuring intensity is the
_______________.

Source
Intensity Level
Threshold of Hearing
(TOH)
0 dB
Rustling Leaves
10 dB
Whisper
20 dB
Normal Conversation
60 dB
Busy Street Traffic
70 dB
Vacuum Cleaner
80 dB
Large Orchestra
98 dB
Walkman at Maximum
Level
100 dB
Front Rows of Rock
Concert
110 dB
Threshold of Pain
130 dB
Military Jet Takeoff
140 dB
Instant Perforation of
Eardrum
160 dB

At normal atmospheric pressure and a
temperature of 20ºC, a sound wave will travel at
approximately 343 m/s; this is approximately
equal to 750 miles/hour.

While this speed may seem fast by human
standards, the speed of a sound wave is slow in
comparison to the speed of a light wave.

Light travels through air at a speed of
approximately 300 000 000 m/s; this is nearly
900 000 times the speed of sound.
Breaking the sound barrier

Accelerating past the speed of sound (750
miles/hour)

_______________ - range of velocities just

below and above the speed of sound.
When jets are in this transonic speed, they
can create the vapor cone effect.
Light Waves
"Is light a wave or a stream
of particles?"

The fact is that light exhibits behaviors which
are characteristic of both waves and
particles.

All waves are known to undergo
_______________ or the bouncing off of an
obstacle.

Most people are very accustomed to the fact that
light waves also undergo _______________.

The reflection of light waves off of a mirrored surface
results in the formation of an image.

A light wave is an _______________ wave
which travels through the vacuum of outer
space.

Light waves are produced by vibrating
electric charges.

Electromagnetic waves exist with an
enormous range of frequencies. This
continuous range of frequencies is known as
the
______________________________.

The entire range of the spectrum is often
broken into specific regions.

Since this narrow band of wavelengths is the
means by which humans see, we refer to it
as the _______________ spectrum.

Normally when we use the term "light," we
are referring to a type of electromagnetic
wave which stimulates the retina of our eyes.

Each individual wavelength within the
spectrum of visible light wavelengths is
representative of a particular color.

When light of that particular
wavelength strikes the retina of our
eye, we perceive that specific color
sensation.

Isaac Newton showed that light shining
through a prism will be separated into its
different wavelengths and will thus show the
various colors that visible light is comprised
of.

The separation of visible light into its different
colors is known as _______________.

Dispersion of visible light produces the
colors:







red (R)
orange (O)
yellow (Y)
green (G)
blue (B)
indigo (I)
violet (V).

It is because of this that visible light is sometimes
referred to as ROY G BIV

The red wavelengths of light are the
_______________ wavelengths and the
violet wavelengths of light are the
_______________ wavelengths.

When all the wavelengths of the visible light
spectrum strike your eye at the same time,
_______________ is perceived.

Visible light is sometimes referred to as
_______________.

Technically speaking, white is not a color at
all, but rather the combination of all the colors
of the visible light spectrum.

If all the wavelengths of the visible light
spectrum give the appearance of white, then
none of the wavelengths would lead to the
appearance of black.

Once more, black is not actually a color.

Technically speaking, black is merely the
absence of the wavelengths of the visible
light spectrum.

So when you are in a room with no lights and
everything around you appears black, it
means that there are no wavelengths of
visible light striking your eye as you look at
the surroundings.

The color of an object is not actually within
the object itself; rather, the color is in the light
which shines upon it that ultimately becomes
reflected or transmitted to our eyes.

We know that the visible light spectrum
consists of a range of frequencies, each of
which corresponds to a specific color.

When visible light strikes an object and a
specific frequency becomes absorbed,
that frequency of light will never make it to
our eyes.

Any visible light which strikes the object
and becomes reflected or transmitted to
our eyes will contribute to the color
appearance of that object.

So the color is not in the object itself, but
in the light which strikes the object.

The only role that the object plays is that it might
contain atoms capable of absorbing one or more
frequencies of the visible light which shine upon it.

If an object absorbs all of the frequencies of visible
light except for the frequency associated with green
light, then the object will appear green.

And if an object absorbs all of the frequencies of
visible light except for the frequency associated with
blue light, then the object will appear blue.

When you look at an object and perceive a
distinct color, you are not necessarily seeing a
single frequency of light.

Consider for instance that you are looking at a
shirt and it appears purple to your eye.

In such an instance, there my be several
frequencies of light striking your eye with
varying degrees of intensity; yet your eye-brain
system interprets the frequencies which strike
your eye and the shirt is decoded as being
"purple."
Color Addition

We have already learned that white is not a
color at all, but rather the presence of all the
frequencies of visible light – the entire
spectrum of visible light.

Combining the range of frequencies in the
visible light spectrum is not the only means of
producing white light.

White light can also be produced by combining only
_______________ distinct frequencies of light,
provided that they are widely separated on the
visible light spectrum.

Any three colors (or frequencies) of light which
produce white light when combined with the correct
intensity are called _______________.

The most common set of primary
colors is
 _______________ (R)
 _______________ (G)
 _______________ (B)

When red, green and blue light are
mixed or added together with the proper
intensity, white (W) light is obtained.

Yellow (Y), magenta (M) and cyan (C) are
sometimes referred to as
_______________ colors of light since
they are produced by the addition of equal
intensities of two primary colors of light.

Any two colors of light which produce white
are said to be _______________ colors of
each other.


The complementary color of red light is cyan light.
Since cyan light is the combination of blue and
green light; and blue and green light when added
to red light will produce white light.
Thus, red light and cyan light (blue + green)
represent a pair of complementary colors; they
add together to produce white light.
Complementary Colors of
Light

Red and Cyan

Green and Magenta

Blue and Yellow
Color Subtraction