Momentum vmp

Mechanical Work dFw

Work against gravity hgmw

Work on an incline plane hgmdF

Gravitational potential energy (GPE) hgmGPE

Translational kinetic energy 2

2

1vmKE

Fahrenheit to Celsius

Celsius to Fahrenheit 32

5

9 32

9

5

CFFC TTTT

Celsius to Kelvin

Kelvin to Celsius 273 273 KCCK TTTT

PART 1: MOMENTUM AND LAW OF CONSERVATION OF

MOMENTUM

Momentum is the “intensity of motion” of a moving object. Momentum describes the “moving inertia”

of an object. Remember, inertia is proportional to mass—the greater the mass of an object, the more

inertia attributed to the object, the more the object will resist changing its state of motion when a force

acts upon it.

Momentum is the product of mass and velocity. Mass is the quantity of matter in an object, and is

proportional to the object’s inertia. Velocity is how fast the object is moving in a straight line at a given

direction. Velocity is a vector, therefore, momentum is also a vector quantity. Momentum may be

positive or negative depending on the direction of motion. The units for momentum are the units of

mass (kg) times the units of velocity (m/s): s

mkg

vmp

p = momentum (s

mkg )

m = mass (kg)

v = velocity (m/s)

Momentum is the product of mass and velocity

The greater the mass of the moving object, the greater the momentum.

The lesser the mass of the moving object, the lesser the momentum.

The faster an object moves, the greater the momentum

The slower and object moves, the lesser the momentum

Example 1: Calculating momentum

Calculate the momentum of a boy riding a skateboard. The

combined mass of the boy and skateboard is 33 kg. The

velocity of the boy and skateboard is 2.5 m/s. s

mkg

smkgp

vmp

5.825.233

Law of Conservation of Momentum

Law of Conservation of Momentum: In a closed system, the total momentum among all objects is

conserved; in a closed system, the sums of the momentums of all objects before they interact must equal

the sums of momentums of all objects after they interact.

In other words: When two or more objects collide, the total momentum of all objects before they collide

must equal the total momentums of all objects after they collide. OR If objects interact, such as in a

collision where two or more objects collide or bump into each other, the total momentum before the

collision must equal the total momentum after collision.

Elastic Collisions: Collisions between two or more objects in which momentum and kinetic energy is

conserved. Object bounce off of each other or conjoin to each other without a loss of energy. (1) No

physical damage between colliding objects. (2) No energy loss due to friction.

Inelastic Collisions: Collisions between two or more objects in which momentum and kinetic energy is

not conserved. Objects collide, the collisions result in a loss of momentum and energy. (1) Physical

damage between colliding objects. (2) Friction causes energy loss.

Illustrative Example: Elastic collision between two objects that rebound.

Two balls are approaching each other and collide. After the collision, the balls rebound in opposite

directions. The sum of momentums of ball 1 and ball 2 before the collision must equal the sum of

momentums after the collision.

PART 2: WORK AND POWER

Work is performed when a constant force is exerted on an object parallel to the direction of the object’s

motion. In other words, work is performed when a force exerted on an object displaces the object

(moves the object in a straight line at a given distance). Work is a vector, and may be positive or

negative depending on the direction of the applied parallel force moving the object. The premise behind

work is that matter has to be physically moved or deformed in some capacity. If the object does not

move, then no work has been performed despite the force applied to the object. The units for work are

Joules.

1 Joule = 1 Nm. The components of joules are the Newton-meter. 1 Newton-meter is equal to 1 joule

of work. (force times displacement). It should be noted that joules is also the unit for energy.

There are four types of work that can be performed on matter: (1) mechanical work, (2) work against

resistance, (3) work against shape, and (4) work against gravity. All forms of work are interrelated and

each can be classified by the other. They all have motion and forces in common.

Mechanical work: Work in which a force physically moves an object over a given displacement

(straight-line distance). Mechanical work is performed when an object is moved by a force from one

location to another.

Work against resistance: Work in which an object is moved, stretched, or pushed by a force against

an opposing force. Work against resistance will always create potential energy. Work against friction

is one form of work against resistance.

Work against shape: If an applied force causes the physical deformation of matter (stretching,

bending, twisting, shattering, compressing, expanding), work is being performed on that matter

because the matter’s shape, size, or consistency has been changed.

Ball 1

m = 2.0 kg

v = 2.0 m/s

Ball 2

m = 3.0 kg

v = -2.0 m/s

Ball 1

m = 2.0 kg

v = -3.2 m/s

Ball 2

m = 3.0 kg

v = 1.47 m/s

Before the collision: ball 1 is in

motion; ball 2 is in motion.

After the collision: ball 2 is in

motion; ball 1 is in motion.

Work against gravity: Work against gravity is a specific case of work against resistance. Work

against gravity is performed when an object is lifted above a permanent surface. Because work is

performed in the up direction, up is opposite the downward acceleration due to gravity, work is being

performed against gravity.

Mechanical Work

Mechanical work is calculated as the product of parallel force times the displacement of the object by

that force.

dFW

W = work (Joules)

F = parallel force moving the object (N)

d = displacement (m)

Note that mechanical work is the product of force times displacement.

The greater the parallel force, the greater the work performed.

The greater the displacement of the object, the greater the work performed.

If the object does not move despite the force being applied, no work will be performed, W = 0.

Work Against Gravity

Work against gravity is the work performed when an object is lifted above a permanent surface to which

it may fall. Gravity on Earth accelerates objects in the down direction, thus when objects are lifted,

work is opposite (up) the direction of gravity (down). Work against gravity is equal to the mass of the

object multiplied by acceleration in Earth’s gravity field by height above the permanent surface.

hgmW

W = work (joules)

m = mass of object (kg)

g = downward acceleration due to gravity (m/s2)

h = absolute height above the permanent surface (m)

The object’s weight (w) is equal to the product of mass times acceleration due to gravity. w = m∙g.

Work performed against gravity is accomplished, the weight of the object is lifted a given height above

the permanent surface.

The greater the mass of the object being lifted, the more work will be performed.

The greater the absolute height above the permanent surface to which the object is lifted, the more

work will be performed.

Displacement (d) Force (F)

Height (m)

Work on an Incline Plane

Incline planes are ramps that connect a lower surface to a higher surface. The incline plane is one

example of a simple machine. Work on an incline plane is accomplished by pushing an object up the

inclined plane surface rather than by lifting the object straight up to its higher position. Just like all

simple machines, incline planes operate by extending the distance over which work is performed such

that effort force is reduced.

Consider the diagram of the incline plane.

The same object can be moved to the

higher position (1) by lifting the object

straight up from the permanent surface to

the top of the incline, and (2) by pushing

the object up the incline’s sloping surface.

In other words, the object can be moved to

the top of the ramp by (1) work against

gravity and (2) mechanical work.

REGARDLESS OF HOW THE OBJECT

GETS TO THE TOP OF THE INCLINE,

THE WORK PERFORMED IS THE SAME

BECAUSE THE OBJECT’S FINAL

POSITION IS THE SAME.

Work against gravity = Mechanical work

dFhgm

WW MWAG

The overall effect is that the parallel force F exerted by pushing the object up the incline plane’s sloping

surface is lesser than lifting the weight of the object (m∙g). The compromise is that the distance up the

incline plane’s sloping surface is greater than the height up the edge of the ramp.

Power

Power is the rate at which work is performed. Power is also the rate at which energy is consumed or

produce by matter. Power is calculated as work divided by time. The units for power are Watts. 1

Watt = 1 J/s. Watts is joules per second.

The faster work is performed, the greater the exerted power.

The slower work is performed, the lesser the exerted power.

t

WP

P = power (Watts)

W = work (Joules)

t = time (s)

Example 1: Mechanical work and power

You push a box with a force of 20 N. The box moves

in a straight line for 20 m. You push it for 12

seconds.

Calculate the work performed on the box.

Calculate the power exerted to push the box.

JmNW

dFW

400 20 20

Wattss

J

t

WP 3.33

12

400

Work against gravity

w = m∙g∙h

Mechanical

work W = F∙d

Example 2: Work against gravity and power

You lift a box from the floor to a shelf 2.0 m above

the floor. The mass of the box is 10 kg. You lift it in

4 seconds.

Calculate the work performed to lift the box.

Calculate the power exerted to lift the box. Wattss

J

t

WP

Jms

mkgW

hgmW

504

200

2000.210102

PART 3: ENERGY

Energy is the capacity to perform work. Energy is the quantity that causes work to be performed and

matter to be transformed. When energy is used or expended, energy causes a force. That force in turn

will move or transform an object, thus producing work. Likewise, when work is performed, work upon

matter will create energy. As a result, energy and work have the ability to produce each other. This is

known as the Work-Energy Theorem. Both work and energy are reported in units of Joules—the same

unit because work and energy can produce or be produced from each other.

ENERGY PRODUCE A FORCE MOVE OR TRANSFORM MATTER WORK

PERFORMED

WORK PERFORMED MOVE OR TRANSFORM MATTER GENERATE ENERGY

Types of Energy

KINETIC ENERGY: energy attributed to matter in motion; energy in moving objects.

Translational KE: KE of an object physically moving from one location to another location.

Rotational KE: KE of an object moving in a circular motion or rotation

Vibrational KE: KE of an object vibrating or moving back-and-forth around a fixed position.

Mechanical KE: KE of machines where a series of interlocking parts (gears, belts, wheels, pistons,

cogs, and levers) are all moving at the same time to make the machine function.

POTENTIAL ENERGY: energy stored in matter to be released; energy created by work against

resistance or against force.

Gravitational PE: PE of an object that has been lifted or suspended above a permanent surface.

Elastic PE: PE of an object that has been stretched or compressed (such as a spring or elastic) and

has the potential to rebound to its original shape.

Chemical Energy: PE of matter where energy is stored in chemical bonds and has the potential to

be released during chemical reactions (fuels, food, photosynthesis, plant matter).

OTHER FORMS OF ENERGY

Electricity: energy where electrons flow through matter under the influence of an electric potential

and electric field.

Thermal Energy: heat energy

Radiant Energy: light energy

Nuclear Energy: energy released during nuclear reactions when the nucleus of an atom

disintegrates or fuses with another atom’s nucleus.

On Earth, > 99.9% of the total sources of energy is directly derived from incoming sunlight (solar

radiation). Solar energy causes atmospheric motion (winds and weather), ocean circulation (waves and

currents), photosynthesis, the production of fossil fuels (coal, petroleum, natural gas), direct heating of

the Earth’s surface. The other < 0.1% of the total energy is derived from Earth’s internal heat

(volcanism and geothermal heat), the moon’s gravity (tidal forces), and the Earth’s rotation.

Gravitational Potential Energy and Translational Kinetic Energy

Gravitational Potential Energy (GPE) Translational Kinetic Energy (KE)

hgmGPE

GPE = gravitational potential energy (joules)

m = mass of lifted or suspended object (kg)

g = acceleration due to gravity (10 m/s2)

h = height above the permanent surface (m)

2

2

1vmKE

KE = translational kinetic energy (joules)

m = mass of object moving (kg)

v = velocity of object in motion (m/s)

All work performed against gravity will produce gravitational potential energy (GPE). GPE is the

energy attributed to an object lifted or suspended above a permanent surface. Like all forms of potential

energy, GPE is “stored” energy. The object has energy that has the potential to be released if the object

was allowed to fall (or slide, walk, or roll if on an incline plane) downward toward the permanent

surface. It is not a coincidence that GPE and work against gravity have the same mathematical equation.

Both are dependent on the absolute vertical distance that an object is raised above the permanent surface

(work), the greater the stored energy in the object if it were allow to fall down to the permanent surface

(GPE). All work against gravity will produce an equal amount of gravitational potential energy.

Translational kinetic energy (KE) is the energy attributed to an object in motion moving from one

location to another. Note that the velocity (v) in the equation is squared—the greater the speed, KE

exponentially increases. For example, if the speed of an object doubles, the KE attributed to that object

increases four-fold. If the speed of an object triples, the KE attributed to that object increases nine-fold.

Example 1: Calculating translational kinetic energy

A baseball is thrown with a velocity of 22 m/s. The

mass of the baseball is 0.40 kg.

Calculate the translational KE of the ball.

Js

mkgKE

vmKE

8.962240.02

1

2

1

2

2

Example 2: Work against gravity and power

You walk up stairs from the first floor to the second

floor of school. The vertical height of the second

floor above the first floor is 4 m. Your mass is 65 kg.

Calculate the gravitational potential energy you

gained by walking up the stairs.

Jms

mkgGPE

hgmGPE

26000.410652

PART 4: LAW OF CONSERVATION OF ENERGY

Law of Conservation of Energy: Energy is neither created nor destroyed, but is transformed from one

form of energy to other forms of energy.

In other words, as energy is used to produce work, one form of energy is changed into other forms of

energy. No energy is lost nor gained during this process—energy is conserved. For example, potential

energy can be converted into translational kinetic energy and thermal energy (via friction) as an object

goes from motionless to moving. If you were to add up the kinetic energy and thermal energy, it would

equal the starting potential energy.

TOTAL ENERGY IN THE SYSTEM = ENERGY 1 + ENERGY 2 + ENERGY 3…

The total energy in an object remains constant. At any given instant, the total energy is equal to the sum

of all forms of energy attributed to that object. Some forms of energy may be greater than other. Over

time, the forms of energy may change proportion or quantity, however, the total energy is still the

same—all forms of energy in that object must always add up to the total energy.

Conservation of GPE and KE

We will consider the total energy of an object that is moving up (against gravity) and down (in favor of

gravity). The object will have changing quantities of GPE and KE depending on the direction the object

moves (up or down). Regardless of the object’s motion, the total energy will always be the sum of the

object’s GPE and KE.

TOT E = GPE + KE

THE SUM OF GPE AND KE MUST

ALWAYS EQUAL THE TOTAL

ENERGY OF THE SYSTEM

Total E = GPE + KE

This is true regardless of the object’s position and direction of motion. The total energy

must always equal the sum of the object’s gravitational potential energy and kinetic energy.

WHEN THE OBJECT IS AT THE

HIGHEST POSITION ABOVE THE

PERMANENT SURFACE.

Total E = 100% GPE + 0% KE

100% of the total energy is stored as GPE. The object is not moving, thus KE = 0. When

the object is at the highest position above the permanent surface, it has maximum GPE.

WHEN THE OBJECT IS AT THE

PERMANENT SURFACE OR

LOWEST POSITION OF MOTION.

Total E = 0% GPE + 100% KE

100% of the total energy is KE because the object is moving the fastest. GPE = 0 because

the object is now at the permanent surface. KE is at the maximum.

OBJECT IS MOVING DOWNWARD

(falling, sliding, rolling).

↓ GPE; ↑ KE

As the object moves downward, GPE is being transformed into KE. GPE will decrease

because the object is moving downward. KE will increase because the object is moving

downward and getting faster as it moves downward.

OBJECT IS MOVING UPWARD

↑ GPE; ↓ KE

As the object moves upward, KE is being transformed into GPE. GPE increases because the

object is moving upward to a higher position above the permanent surface. KE is decreasing

because the object is slowing as it moves upward.

OBJECT IS HALF-WAY BETWEEN

HIGHEST POINT AND

PERMANENT SURFACE

50% GPE; 50% KE

50% of the energy is GPE because the object is halfway between the highest point and

permanent surface. 50% is KE because 100% E – 50% GPE = 50% KE. This is true

regardless if the object is moving up or down.

At the gnarly skate park, the skateboarding dude thrashes

the U. At the cusp of the U (highest position), the total

energy is equal to 100% GPE—the dude is not moving

(0% KE). The dude coasts down the ramp. His height

above the permanent surface is decreasing and his speed

down the ramp is increasing—GPE is getting smaller,

KE is getting greater. GPE is being transformed into KE.

At the bottom of the ramp, the dude is at the permanent

surface. GPE is 0% because the dude is at the permanent

surface, KE is 100% because the child is moving the

fastest.

As the dude coasts up the opposite ramp under his inertia

(no external energy pushing or pulling him), his height

above the permanent surface is increasing—GPE is

getting greater. His speed in the upward direction is

getting slower—KE is decreasing. KE is being

transformed into GPE.

The dude reaches the highest point on the opposing

ramp—100% GPE and 0% KE.

At the highest position above the permanent surface

TOTAL E = 100% GPE + 0% KE

At impact with the permanent surface

TOTAL E = 0% GPE + 100% KE

At halfway between the highest position and permanent surface

TOTAL E = 50% GPE + 50% KE

As the object moves downward, GPE

decreases because object’s height above

the permanent surface is decreasing.

KE increases because the object’s

velocity is getting faster the farther it

moves downward.

100% GPE

0% KE

100% GPE

0% KE

0% GPE

100% KE

↓ GPE

↑ KE

↑ GPE

↓ KE

100% GPE

0% KE

100% GPE

0% KE

0% GPE

100% KE

↓ GPE

↑ KE

↑ GPE

↓ KE

PART 5: TEMPERATURE

There are four types of kinetic energy: Translational KE, Mechanical KE, Rotational KE, and

Vibrational KE. Kinetic energy is proportional to the square of the matter’s velocity. The faster objects

move, the more KE the objects have; the slower objects move, the lesser the KE the objects have.

Translational KE and rotational KE tend to be on the large scale: whole objects move at a given speed

from point A to point B, or whole object spins. It is easy to see and measure those objects moving or

spinning. Conversely, vibrational KE, tends to describe smaller scale motions in matter, at the

molecular level. Molecules cannot be seen as easily, or their vibrations cannot be measured easily,

because they are microscopic. Most vibrations involve molecules or atoms that move back-and-forth in

repetitive motions, knocking into each other, especially when energy disturbs them or when waves pass

through the object. Vibrations can occur when the whole object translates or rotates. Vibrations can

occur when whole object is not translating or rotating. So, it can be said that objects have both “macro”

motion and KE (large-scale to the whole object, easily seen) and “micro” motion and KE (very small

scale to the molecules that make up the object, not easily seen).

Temperature

Temperature is often called the measure of the “hotness” or “coldness” of matter. Temperature is NOT

a measure of heat, however, temperature may be an indicator of heat or the internal energy in matter.

Temperature is defined as the measure of the average kinetic energy of matter. The hotness or coldness

of matter is directly related to the kinetic energy of molecules in the matter, a combination of both the

“macro” KE and the “micro” KE within the object or matter. The relationship between KE and

temperature is:

The faster the molecules that make up the object move, the hotter the object will feel, the greater its

temperature.

The slower the molecules that make up the object move, the cooler the object will feel, the lesser its

temperature.

The diagram to the left shows two different gases. The molecules in the

upper image are moving faster (greater KE) than the molecules in the

lower image (lesser KE). The gas in the upper image has a greater

temperature than the gas in the lower image.

Another important factor that affects how hot or how cold an object or

matter will be is how dense or crowded the moving molecules are. When

molecules are moving (have a lot of KE) and are packed tightly together,

molecules will collide more frequently because they are physically closer

to each other. When molecules are moving and are widely spaced (not

compacted), molecules will collide less frequently because they are

physically farther apart.

The more compact (dense) the matter, the more frequently moving

molecules collide, the greater the temperature.

The less compact (less dense) the matter, the less frequently moving

molecules collide, the lesser the temperature.

Temperature Scales

There are three temperature scales: Fahrenheit (ºF), Celsius (ºC), and Kelvin (K).

Fahrenheit is the “English Standard” unit for measuring and reporting temperature. The Fahrenheit

scale is based on using a mercury-filled glass bulb thermometer to measure human body temperature as

a single reference point. In the 1700s, human body temperature was defined as 100ºF; today, accurate

HBT is 98.6ºF. Temperatures in Fahrenheit may be positive or negative.

Celsius is the metric unit for measuring and reporting temperature under most circumstances. The

Celsius scale is based on using an alcohol-filled glass bulb thermometer with the melting point

temperature of water (0ºC) and boiling point temperature of water (100ºC) as two reference points.

Celsius is related to Kelvin, the scientific unit of temperature. Temperatures in Celsius may be positive

(warmer than the MPT of water) or negative (cooler than the MPT of water).

Kelvin is the scientific unit for temperature. Kelvin (not degrees Kelvin) is an absolute scale (starts at

zero) relative to absolute zero and scaled with the same increments as the Celsius scale. No matter or

space in our observable universe can achieve a temperature lesser than absolute zero—it is the

lowermost temperature. Absolute zero has a value of 0 Kelvin. All temperatures in the Kelvin

temperature scale are positive numbers because all measurable temperatures are warmer than absolute

zero.

Convert Kelvin to

Celsius

273 KC

Convert Celsius to

Kelvin

273CK

Convert Celsius to

Fahrenheit

325

9

CF

Convert Fahrenheit to

Celsius

329

5 FC

Examples of Temperature Kelvin Celsius Fahrenheit

Surface of temp of Sun 5800 K 5537ºC 9,999ºF

Boiling point temp of H2O 373 K 100ºC 212ºF

Human body temp 310 K 37ºC 98.6ºF

Melting point temp of H2O 273 K 0ºC 32ºF

Zero Fahrenheit 255 K -18ºC 0ºF

Absolute Zero 0 K -273ºC -459ºF

States of Matter and Their Kinetic Energies

Gases have the greatest amount of kinetic energy, and gas molecules have the greatest random motion.

Gas molecules move independently of each other at very fast velocities. Most of the KE of gas

molecules is translational KE—moving from one location to another at a given velocity. At room

temperature, gas molecules can move hundreds of m/s. A very, very small proportion of the KE in gases

is vibrational KE between bonded atoms.

Fluids (liquids) have a moderate amount of kinetic energy—much less KE than gases but more than

solids. The molecules in fluids have moderate random motion, however, those molecules do not move

independently of each other like the molecules in gases. Fluid molecules touch other fluid molecules,

and they move by flowing over and around each other. Fluid molecules also move significantly slower

than gas molecules.

Solids have the least amount of kinetic energy—much less KE than fluids. The molecules in solids have

the least random motion—random motion approaches zero. The molecules and atoms that compose

solids are in a fixed position—they cannot translate or move from one location to another. Unless a

force sets the whole object into motion, almost 100% of a solid’s KE is vibrational KE. Molecules and

atoms vibrate, or move very fast back-and-forth around their fixed position. The warmer or hotter the

solid, the faster molecules vibrate; the cooler the solid, the slower molecules vibrate. Even when matter

is cold, the molecules in solids vibrate, albeit very slowly.

The diagram shows the randomness of

motion of the different states of matter.

Gases have the greatest KE and random

motion—molecules tend not to touch each

other and move independently of each other

at great speeds. In contrast, solids have the

least KE and random motion. The molecules

cannot randomly move or translate. Instead,

the molecules in solids are fixed in position

and can only vibrate back and force against

each other around their fixed position.

PART 6: HEAT AND HEAT TRANSFER

Heat is defined as the change or transfer of internal energy from one object to another. Heat cannot be

directly measured, but is indicated by temperature changes or the change in internal energy. As energy

is transferred from one object to another, the transferred energy may cause a change in temperature. The

object whose temperature increases is gaining energy, molecules move faster (increased KE)—a gain in

heat. The object whose temperature decreases is releasing energy, molecules move slower (decreased

KE)—a loss in heat.

Internal energy is the energy in matter that is contained within the molecules that make up the matter.

In contrast, external energy is the overall energy of the whole object. For example, a cloud is made of

billions of very small microdroplets of water. The cloud’s external energy would be the entire cloud

moving across the sky. The cloud’s internal energy would be the individual water molecules and

microdroplets rotating and the H-O-H atoms in each molecule vibrating.

Examples of internal energy include

Kinetic energy of individual molecules (translational KE for gases and fluids, rotational KE, and

vibrational KE for solids), not the KE of the whole object if in motion.

Chemical potential energy (energy stored because of chemical bonds between atoms) that may be

released by chemical reactions.

Potential energy stored because of electrostatic attraction or repulsion (opposite charges attract each

other, like charges repel each other.) Molecules are held together because they attract other molecules.

Heat and Energy Transfer

When objects or matter interact, energy will be transferred between them. Energy (heat) can be

transferred by conduction, by convection, or by radiation.

Conduction is the transfer of energy and heat by contact or touch. Heat and energy is passed through

matter because of molecule-to-molecule vibration. Conduction is most efficient through solids because

atoms and molecules are stacked side-by-side and can only interact with adjacent molecules by vibration.

How conduction works

In the diagram to the left, the end of the metal

rod is placed into fire. At time 1, when the end

of the rod is placed into the fire, the end of the

rod gains energy and becomes hot. The energy

from the fire causes the metal atoms and

molecules to vibrate faster and faster, causing

the temperature of the metal in the rod to

increase. Over time, the energy is transferred

through the metal rod away from the fire. This

is indicated by the increase in the temperature

of the rod farther away from where the rod

touches the fire.

Insulators and Conductors

Insulators are materials that slow or prevent the

transfer of energy.

Materials that insulate against heat and energy

change temperature slowly—they become hotter

and colder very slowly because that material does

not conduct energy very well.

Examples of insulators are wood, plastic, rubber,

glass, Styrofoam, water, and air.

Conductors are materials that allow the transfer of

energy.

Materials that conduct heat and energy change

temperature quickly—they become hotter and

colder very quickly because that material will

allow for heat or energy to pass through them very

well.

Examples of conductors are metals and salts.

Radiation is the transfer of energy by light passing through space or air. Radiation means light. Radiant

energy means light energy. All objects release at least one form of energy in the form of radiation.

Remember, the human eye is only able to see visible light. The other forms of light (gamma, x-ray, UV,

infrared, microwave, and radiowave are invisible to the human eye).

An example of energy transfer by radiation is the sun and the Earth. Sunlight

(the sun’s starlight) moves outward through space from the sun. Some of that

sunlight reaches Earth and is intercepted by the Earth’s system. The sunlight

that passes through the Earth’s atmosphere is transformed by the Earth system

(photosynthesis, ocean circulation, atmospheric circulation, direct heating of

the Earth’s surface). Eventually, Earth radiates an equal amount of energy

back to space in the form of infrared (a form of light that humans cannot see).

If Earth did not release infrared energy back to space, the Earth’s atmosphere

would continuously build up heat and become hotter and hotter with time.

time 1

time 2

time 3

180ºC 40ºC 25ºC 25ºC25ºC

250ºC 150ºC 40ºC 25ºC90ºC

250ºC 230ºC 180ºC 40ºC210ºC

Convection is the transfer of energy and heat by

matter that moves in vertical circulation.

Convection occurs in fluids and gases because

fluids and gases are mobile—they can move and

flow. Warmer air or warmer water is carried by

flowing currents into regions that are cooler.

Convection cannot occur in solids.

Warm air is less dense than cold air. As a result of

this density difference, warmer air rises and colder

air sinks. As the warmer air rises, it releases heat

(the arrows) to the cooler air into which it moves.

Eventually, that air becomes cold and dense, and

will move downward.

Thermodynamic Equilibrium

Thermodynamic equilibrium is the condition where equal amounts of energy are transferred between

two or more different objects or forms of matter that are in contact. If energy is not uniformly

distributed across matter, or proportionate between the two different materials in contact, or if the two

different materials are not the same temperature, energy will move from where it is more concentrated

(hotter) to where it less concentrated (colder). If the given enough time, the two materials that are in

contact may achieve a condition of thermodynamic equilibrium. At energy equilibrium, (1) the two

materials that are in contact reach the same temperature, (2) the two materials have proportionate

quantities of heat, and (3) the net rate of heat/energy transfer between the two materials is equal and

opposite—the amount leaving one material to the other is equal and opposite the amount entering the

other, and vice-versa.

Left: Conditions at disequilibrium.

One material is hotter, the other

material is cooler. More energy is

being transferred from the hotter

matter to the cooler matter.

Right: Conditions at equilibrium.

Energy is being transferred equally

between the two forms of matter.

Both forms at matter are at the same

temperature.

HEAT SOURCE

Cooler

System

HOTTER

Surroundings

COOLER

System

Surroundings

PART 7: LAWS OF THERMODYNAMICS

There are four laws of thermodynamics. The laws of thermodynamics describe how energy is

transferred between different objects or within matter. The laws of thermodynamics tell how energy

moves and transforms matter, but they do not explain why energy moves or why energy transforms

matter.

0th

Law of Thermodynamics: If any two or more objects or forms of matter that are in direct contact

with each other are at the same temperature, those objects or those forms of matter are in a state of

thermodynamic equilibrium.

In other words: When objects are touching and they are at the

same temperature, the objects are exchanging equal amounts

of energy. The amount of energy transferred between the

objects is equal and opposite—the amount leaving each is

equal to the amount gained back by each. Because equal

amounts of energy are leaving the object and being transferred

back to the object at the same time, the total amount of energy

in the object never changes—it remains “equal” or in a state

of equilibrium.

In the diagram above, both blocks are touching and are at the same temperature. Notice that energy (the

arrows) is moving equally and opposite from one block to the other. Because an equal amount of energy

is moving out of and into each block simultaneously, the total energy in each block does not change—

the amount lost is equal to the amount gained back.

1st Law of Thermodynamics: When heat energy is added to matter, the total heat added to the matter

minus the work performed by the matter on its surroundings is equal to the internal energy of the matter.

In other words: When matter gains heat or energy, that matter has the potential to perform work on the

matter surrounding it. When objects become hot, they can change shape/size (work against shape) or

move objects (work against resistance, mechanical work). The more energy or heat an object gains, the

more work that object can perform on matter that surrounds it.

When matter gains energy, the temperature of the matter increases (becomes hotter).

When matter performs work on its surroundings, energy is being transformed to work, the temperature

of the matter performing the work decreases (becomes colder).

25ºC 25ºC

20ºC

Add heat

40ºC

20ºC

The heated air inside the balloon expands in volume. The hotter expanding air pushes outward on the

air around it (performing work). As the air expands, it cools because work is being performed on the

rubber part of the balloon (work against shape) and by pushing away the air around the balloon

(mechanical work) to allow it to grow bigger—the KE of the molecules is performing work, slowing the

molecules down and lowering the temperature.

2nd Law of Thermodynamics: The 2nd

law of thermodynamics states (1) energy will spontaneously

move down the energy gradient from matter with greater energy to matter with lesser energy; (2) heat

energy always moves down the temperature gradient from matter with greater temperatures to matter

with lesser temperatures; and (3) matter and energy will spontaneously move to a state of greater

randomness and disorder, or entropy.

In other words: Energy will try to spontaneously “spread itself out evenly.” If energy is more

concentrated in one region of matter and less concentrated in another region of matter, the energy will

redistribute itself from where it is more concentrated to where it is less concentrated (diagram 1). Over

time, the energy/heat will become uniformly dispersed across the entire matter (diagram 2). The

redistribution of energy occurs by conduction, convection, or radiation, or a combination of the three

mechanisms of heat transfer.

Diagram 1

Diagram 2

3rd

Law of Thermodynamics: Absolute zero is a real number, and represents the lowermost temperature

in the universe. Any matter that achieves absolute zero will be a crystalline solid that has zero heat and

zero internal energy.

No matter in the universe actually exists at absolute zero. The coldest intergalactic regions of space

have temperatures 2-3º K. Even with modern technology, it is impossible to extract all energy from

matter and lower its temperature to absolute zero. Absolute zero is a temperature value based on the

volume-temperature endpoint of an ideal gas. If an ideal gas, such as N2 gas, is cooled in temperature,

for each degree Celsius that the gas is cooled, its volume contracts by 1/273 units. Hence, absolute zero

0 Kelvin is -273 Celsius.

Entropy

Entropy is a phenomenon described in the 2nd

Law of Thermodynamics. Entropy is the measure of

disorder or randomness of molecules in matter. The greater the KE and random motion of molecules,

the more entropy the matter has. Gases have the greatest entropy because they have the most random

motion and greatest KE. Solids have the least entropy because they have the least random motion and

lowest KE. Entropy is a natural progression. Matter that is well ordered will “fall apart” or become less

ordered with time. Matter will spontaneously move toward more randomness and toward more disorder.

HOT COLD Net movement of energy

Temperature Gradient

Uniform Temperature

The consequence of entropy is to redistribute matter and energy evenly. Molecules of matter will try to

be evenly spaced apart. Energy will be spread evenly across the matter or space in which it exists. The

entropy of the universe is always increasing. Our universe is moving toward greater and greater entropy

because our universe is expanding—the matter and energy in our universe is being spread over an ever

increasing volume of space and time.

If you put a drop of food

coloring in water, the food

coloring will naturally disperse

throughout the water.

Molecules of food coloring

will become evenly

distributed.

If allowed gas molecules will

diffuse and move such that

they evenly distribute

themselves in the entire space.

PART 8: PHASE CHANGES AND ENERGY TRANSFER

When we discuss the direction of energy movement, we talk about the system and the surroundings.

The system is the object or matter that you are investigating. The system is the object or matter you are

interested in analyzing. The surroundings is the other objects or matter that surround, interact with, or

touch the system. When we talk about energy movement from one location to another, the system is the

point of reference. The heat and energy is moved from one location to another by conduction,

convection, and radiation according to the 2nd

Law of the Thermodynamics: heat spontaneously moves

down the energy gradient from regions that are hotter to regions that are colder.

Endothermic and Exothermic Processes

Endothermic (endo = into) refers to energy

transfer where heat/energy moves from the

surroundings into the system. The system gains

heat and energy from the matter around it.

Endothermic heat transfer occurs when the

surroundings have greater energy, heat, or

temperature than the system. The system is colder,

the surroundings are warmer. Heat flows from the

surroundings into the system.

Exothermic (exo = exiting) refers to energy

transfer where heat/energy moves from the system

to the surroundings. The system loses heat and

energy and gives it to the matter around it.

Exothermic heat transfer occurs when the system

has greater energy, heat, or temperature than the

surroundings. The surroundings are colder, the

system is warmer. Heat flows from the system to

the surroundings.

Endothermic heat transfer

Over time, the system warms (gaining heat) and

the surroundings cool (releasing heat)

Exothermic heat transfer

Over time, the surroundings warm (gaining heat)

and the system cools (releasing heat).

When matter gains heat energy (energy is transferred from the surroundings), the temperature of the

matter will increase and become hotter. This happens because when matter gains heat, the kinetic

energy (translational, vibrational, rotational) of the molecules increases. When matter releases heat

energy (energy is transferred to the surroundings), the temperature of the matter will decrease and

become colder. This happens because when matter releases or loses energy, the kinetic energy

(translationa, vibrationa, and rotational) of the molecules decreases. For example: the molecules in a

hotter solid vibrate much faster than the molecules in a colder solid.

If you sit a cup of hot coffee on the table and walk away, over time the temperature of

the liquid coffee will decrease (become colder). This occurs because the temperature of

the coffee is warmer than the temperature of the air in the room. Heat will move from

the coffee to the air in the room. If given a long enough time, the temperature of the

coffee will cool to the temperature of the air in the room.

States of Matter

Solid Fluid Gas

Rigid shape. Volume that remains

constant.

Changing shape that assumes the

shape of the container with a

gravitational surface. Volume that

“remains constant”.

Fills the entire volume of its

container. Volume not constant,

volume changes with temperature.

All molecules in contact with other

molecules in a tightly-packed

arrangement.

Molecules in contact with other

molecules, molecules are in motion.

Molecules flow over each other.

Molecules not in contact with other

molecules. Molecules moving

independently and randomly in 3-

dimensional space.

Lowest energy: vibrational KE.

Intermediate energy: mostly

translational KE with some

rotational and vibrational.

Greatest energy: mostly

translational KE with some

rotational and vibrational.

Least entropy. Most ordered

arrangement of molecules.

Intermediate entropy. Disordered

arrangement of molecules.

Most entropy. Highly disordered

and random motion of molecules.

System

40ºC

Surroundings

25ºC

Surroundings

25ºC

Surroundings

25ºC

Surroundings

25ºC

System

25ºC

Surroundings

40ºC

Surroundings

40ºC

Surroundings

40ºC

Surroundings

40ºC

Phase Changes

Phase changes occur when the states of matter change from one state to another state, like from gas to

fluid or solid to fluid. Phase changes do not change the chemical composition of the matter, only the

physical state. For example, liquid water, ice, and steam, have the same chemical formula and

chemistry: H2O. The water molecules did not change, only their arrangement and the amount of kinetic

energy.

Phase changes occur because matter gains heat from the surroundings (endothermic) or releases heat to

the surroundings (exothermic) such that the molecules that make up the matter change their contact with

other molecules by having more or less KE. Temperature does not change as long as the phase change

is in progress—all gain and release of energy affects the molecules’ arrangement.

Endothermic Phase Changes: When a substance undergoes melting, evaporation, boiling, or

sublimation, that substance must gain heat from the surroundings in order for the phase change to

occur. The molecules in the new phase are more energetic, moving with more random motion, and

moving faster (greater heat, greater entropy, greater KE).

Melting Solid + Heat

Fluid

A solid gains heat and is transformed to a fluid. Melting occurs at the

melting point temperature.

Evaporation Fluid + Heat

Gas

A fluid gains heat and is transformed to a gas. Evaporation occurs at

temperatures between the melting point temperature and the boiling

point temperature.

Boiling Fluid + Heat

Gas

A fluid gains heat and is transformed to a gas. Boiling occurs at the

boiling point temperature.

Sublimation Solid + Heat

Gas

A solid gains heat and is transformed directly to a gas without turning

into a fluid first. Sublimation generally occurs at temperatures below

the melting point temperature.

Exothermic Phase Changes: When a substance undergoes condensation, freezing, or deposition, that

substance releases heat to the surroundings in order for the phase change to occur. The molecules in

the new phase are less energetic, moving with less random motion, and moving slower (lesser heat,

lesser entropy, lesser KE)

Condensation Gas Fluid +

Heat

A gas releases heat and is transformed to a fluid. Condensation

occurs at temperatures between the melting point temperature and the

boiling point temperature.

Freezing Fluid Solid +

Heat

A fluid releases heat and is transformed to a solid. Freezing occurs at

the melting point temperature.

Deposition Gas Solid +

Heat

A gas releases heat and is transformed directly to a solid without

turning into a fluid first. Deposition occurs at temperature below the

melting point temperature.

The boiling point temperature (BPT) of a substance is the temperature at which (1) a fluid boils to a gas

(if gaining heat) and (2) a gas condenses to a fluid (if releasing heat). At standard atmospheric pressure,

the substance must exist as a gas at all temperatures greater than the BPT and must exist as a fluid at

temperatures lesser than the BPT.

The melting point temperature (MPT) of a substance is the temperature at which (1) a solid melts to a

fluid (if gaining heat) and (2) a fluid freezes to a solid (if releasing heat). At standard atmospheric

pressure, the substance must exist as a solid at all temperatures below the MPT and must exist as a fluid

at temperatures greater than the MPT.

Substance MPT (Celsius) BPT (Celsius) Substance

MPT

(Celsius)

BPT

(Celsius)

Water 0 100 Aluminum 660 2520

Ozone -192 -110 Iron 1538 2862

Ammonia -78 -33 Copper 1085 2562

Methane -182 -162 Gold 1065 2856

Propane -188 -42 Wax 65 370

Solid Fluid Gas melting

freezing

boiling

condensation

deposition

Sublimation

Increasing KE, energy, random motion

How phase changes occur.

The graphs are phase change diagrams. The x-axis is the heat added or released by the matter. The y-

axis is the temperature of the matter.

The matter starts as a cold solid. When

heat is added to the solid, it warms

(temperature increases). The temperature

of the solid will increase with more and

more heat gained until the temperature

reaches the melting point temperature

(MPT). At the MPT, melting occurs.

While melting occurs, the temperature does

not change (the line under the word

“Melting” is horizontal). When the

melting is complete, only fluid exists.

When heat is added to the fluid, the fluid

warms (temperature increases). The

temperature of the fluid will increase with

more and more heat gained until the

temperature reaches the boiling point temperature (BPT). At the BPT, boiling occurs. While boiling

occurs, the temperature does not change (the line under the word boiling” is horizontal). When the boiling

is complete, only gas exists. When heat is added to the gas, the gas warms (temperature increases).

In this phase change diagram, the matter

starts as a gas at a very high temperature

(very hot). As the gas releases heat to its

surroundings, the gas cools (temperature

decreases). The temperature of the gas will

decrease with more and more heat released

until the temperature reaches the BPT. At

the BPT, condensation occurs. While

condensation occurs, the temperature does

not change (line above the word

“Condensation” is horizontal). When the

condensation is complete, only fluid exists.

When heat is released by the fluid to the surroundings, the fluid cools (temperature decreases). The

temperature of the fluid will decrease with more and more heat released until the temperature reaches the

MPT. At the MPT, freezing occurs. While freezing occurs, the temperature does not change (the line above

the word “freezing” is horizontal). When freezing is complete, only solid exists. When heat is released by

the solid to the surroundings, the solid cools (temperature decreases).

Heat added to the substance

Tem

per

ature

Melting

Boiling

Gas

Fluid

Solid

BPT

MPT

Heat added to the substance

Tem

per

ature

Freezing

Condensation

Gas

Fluid

Solid

BPT

MPT