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 downwardly-moving 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.

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 = ma1 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 action-reaction 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.

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 pole-vaulting 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?

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