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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