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Matter and Energy
States of Matter
States of matter are the different forms in which matter can exist.
Water is a great example because we often experience water as a solid, liquid, and a gas. In all three
states, water is still water.
It has the same chemical makeup and the same chemical properties. That’s because the state of
matter is a physical property.
Solids
Ice is an example of solid matter. A solid is matter that has a fixed volume and a fixed shape.
Salt and are examples of crystalline solids. The particles of crystalline solids are arranged in a regular
repeating pattern.
The steaks and candle wax are examples of amorphous ("shapeless") solids. Their particles have no
definite pattern.
Liquids
Ocean water is an example of a liquid. A liquid is matter that has a fixed volume but not a fixed
shape.
Instead, a liquid takes the shape of its container. If the volume of a liquid is less than the volume of
its container, the top surface will be exposed to the air.
Two interesting properties of liquids are surface tension and viscosity.
• Surface tension is a force that pulls particles at the exposed surface of a liquid toward other liquid
particles. Surface tension explains why water forms droplets.
Viscosity is a liquid’s resistance to flowing. Thicker liquids are more viscous than thinner liquids. For
example, honey is more viscous than the vinegar.
Gases
Water vapor is an example of a gas. A gas is matter that has neither a fixed volume nor a fixed shape.
Instead, a gas takes both the volume and the shape of its container. It spreads out to take up all
available space.
Plasmas
You’re probably less familiar with plasmas than with solids, liquids, and gases. Yet, most of the
universe consists of plasma.
Plasma is a state of matter that resembles a gas but has certain properties that a gas does not have.
Like a gas, plasma lacks a fixed volume and shape. Unlike a gas, plasma can conduct electricity and
respond to magnetism.
That’s because plasma contains charged particles called ions. This gives plasma other interesting
properties. For example, it glows with light.
Where can you find plasmas?
The sun and other stars consist of plasma.
Plasmas are also found naturally in lightning and the polar auroras (northern and southern lights).
Artificial plasmas are found in fluorescent lights, plasma TV screens, and plasma balls
Kinetic Theory of Matter
How can ice, water, and steam all be made of the same matter yet have such different properties?
Energy and Matter
Why do different states of matter have different properties? It’s because of differences in energy at
the level of atoms and molecules, the tiny particles that make up matter.
Energy is defined as the ability to cause changes in matter. You can change energy from one form to
another when you lift your arm or take a step. In each case, energy is used to move matter —you.
The energy of moving matter is called kinetic energy.
Kinetic Theory of Matter
The particles that make up matter are also constantly moving. They have kinetic energy. The theory
that all matter consists of constantly moving particles is called the kinetic theory of matter.
It may not seem like it but even the molecules, or tiny particles, that make up your desk are slightly
vibrating in place.
Energy and States of Matter
Particles of matter of the same substance, such as the same element, are attracted to one another.
The force of attraction tends to pull the particles closer together.
The particles need a lot of kinetic energy to overcome the force of attraction and move apart. It’s
like a tug of war between opposing forces.
The kinetic energy of individual particles is on one side, and the force of attraction between
different particles is on the other side. The outcome of the "war" depends on the state of matter.
Energy is always involved in changes of state. Matter either loses or absorbs energy when it changes
from one state to another.
For example, when matter changes from a liquid to a solid, it loses energy. The opposite happens
when matter changes from a solid to a liquid. For a solid to change to a liquid, matter must absorb
energy from its surroundings.
The amount of energy in matter can be measured with a thermometer. That’s because a
thermometer measures temperature, and temperature is the average kinetic energy of the particles
of matter.
Solids
In solids, particles don’t have enough kinetic energy to overcome the force of attraction between
them.
The particles are packed closely together and cannot move around. All they can do is vibrate. This
explains why solids have a fixed volume and shape.
Changes Between Solids and Liquids
Removing enough energy from a liquid will slow the movement of molecules resulting in freezing.
Adding enough energy to a solid may result in melting.
Freezing and melting are words used to describe a phase change between a solid and a liquid.
Liquids
In liquids, particles have enough kinetic energy to partly overcome the force of attraction between
them.
They can slide past one another but not pull completely apart. This explains why liquids can change
shape but have a fixed volume.
Changes Between Liquids and Gases
If enough energy is added to a liquid to bring the liquid to a boil it will begin to phase change into a
gas through a process called vaporization.
If a gas cools down and loses energy, such as water vapor in a bathroom touching a cool mirror, it
will condense back into a liquid from a gas through a process called condensation.
Gases
In gases, particles have a lot of kinetic energy. They can completely overcome the force of attraction
between them and move apart.
This explains why gases have neither a fixed volume nor a fixed shape.
Plasmas
We interact with other states of matter constantly but plasmas are a little different.
Think of a plasma as a gas; a super charged gas that is so energetic that the electrons of individual
atoms have been separated in to negatively charged electrons and positively charged ions.
Of the four states of matter, this state has the highest kinetic energy.
Properties of Matter
Matter comes in many forms and different types of matter have distinct properties that differentiate
them from others.
What is Matter?
Both you and the speck of dust consist of atoms of matter. So does the ground beneath your feet.
In fact, everything you can see and touch is made of matter.
The only things that aren’t matter are forms of energy, such as light and sound. Although forms of
energy are not matter, the air and other substances they travel through are.
So what is matter? Matter is defined as anything that has mass and volume.
Mass
Mass is the amount of matter in a substance or object. Mass is commonly measured with a balance.
It allows an object to be matched with other objects of known mass.
SI units for mass are the kilogram, but for smaller masses grams are often used instead.
Mass Verses Weight
The more matter an object contains, generally the more it weighs. However, weight is not the same
thing as mass.
Weight is a measure of the force of gravity pulling on an object. It is measured with a scale, like a
bathroom scale.
The scale detects how forcefully objects in the pan are being pulled downward by the force of
gravity.
An object with more mass is pulled by gravity with greater force, so mass and weight are closely
related. However, the weight of an object can change if the force of gravity changes, even while the
mass of the object remains constant.
Neil Armstrong weighed less on the moon than he did on Earth because the moon’s gravity is
weaker than Earth’s. His mass, on the other hand, did not change. He still contained the same
amount of matter on the moon as he did on Earth.
Volume
The amount of space matter takes up is its volume. How the volume of matter is measured depends
on its state.
The volume of liquids is measured with measuring containers. In the kitchen, liquid volume is
usually measured with measuring cups or spoons.
In the lab, liquid volume is measured with containers such as graduated cylinders. Units in the metric
system for liquid volume include liters (L) and milliliters (mL).
The volume of gases depends on the volume of their container. That’s because gases expand to fill
whatever space is available to them.
For example, as you drink water from a bottle, air rushes in to take the place of the water. An
"empty" liter bottle actually holds a liter of air. How could you find the volume of air in an "empty“
room?
The volume of regularly shaped solids can be calculated from their dimensions. For example, the
volume of a rectangular solid is the product of its length, width, and height (lxwxh).
For solids that have irregular shapes, the displacement method is used to measure volume.
The SI unit for solid volumes is cubic meters (m3). However, cubic centimeters (cm3) are often used
for smaller volume measurements.
Physical Properties of Matter
Matter has many properties. Some are physical properties. Physical properties of matter are
properties that can be measured or observed without matter changing to a different substance.
For example, whether a given substance normally exists as a solid, liquid, or gas is a physical
property.
Consider water. It is a liquid at room temperature, but if it freezes and changes to ice, it is still water.
Generally, physical properties are things you can see, hear, smell, or feel with your senses.
Examples of Physical Properties
Physical properties include the state of matter and its color and odor. For example, oxygen is a
colorless, odorless gas. Chlorine is a greenish gas with a strong, sharp odor.
Other physical properties include hardness, freezing and boiling points, the ability to dissolve in
other substances, and the ability to conduct heat or electricity.
Density
Density is an important physical property of matter. It reflects how closely packed the particles of
matter are. Density is calculated from the amount of mass in a given volume of matter, using the
formula:
To better understand density, think about a bowling ball and a volleyball. The bowling ball feels
heavy. It is solid all the way through. It contains a lot of tightly packed particles of matter.
In contrast, the volleyball feels light. It is full of air. It contains fewer, more widely spaced particles
of matter. Both balls have about the same volume, but the bowling ball has a much greater mass. Its
matter is denser.
Energy
Potential and Kinetic Energy
Energy due to position and energy due to motion.
Energy
The concept of energy was first introduced in the chapter "States of Matter," where it is defined as
the ability to cause change in matter. Energy can also be defined as the ability to do work.
Work is done whenever a force is used to move matter. When work is done, energy is transferred
from one object to another.
For example, when a batter uses energy to swing the bat, she transfers energy to the bat. The
moving bat, in turn, transfers energy to the ball.
Kinetic Energy
Kinetic energy is the energy of moving matter. Anything that is moving has kinetic energy —from
the atoms in matter to the planets in solar systems. Things with kinetic energy can do work.
The amount of kinetic energy in a moving object depends on its mass and velocity. An object with
greater mass or greater velocity has more kinetic energy.
Potential Energy
In many parts of the world, trees lose their leaves in autumn.
The leaves turn color and then fall from the trees to the ground. As the leaves are falling, they have
kinetic energy.
While they are still attached to the trees they also have energy, but it’s not because of motion.
Instead, they have stored energy, called potential energy.
An object has potential energy because of its position or shape. For example leaves on trees have
potential energy because they could fall due to the pull of gravity.
Gravitational Potential Energy
Potential energy due to the position of an object above Earth is called gravitational potential energy.
Like the leaves on trees, anything that is raised up above Earth’s surface has the potential to fall
because of gravity.
Gravitational potential energy depends on an object’s weight and its height above the ground.
Elastic Potential Energy
Potential energy due to an object’s shape is called elastic potential energy. This energy results when
elastic objects are stretched or compressed. Their elasticity gives them the potential to return to their
original shape.
For example, when a rubber band in has been stretched, but it will spring back to its original shape
when released.
Conservation of Energy
The law of conservation of energy applies to energy conversions. Energy is not used up when it
changes form, although some energy may be used to overcome friction, and this energy is usually
given off as heat.
For example, a diver’s kinetic energy at the bottom of his fall is the same as his potential energy
when he was on the diving board, except for a small amount of heat resulting from friction with the
air as he falls.
Forms of Energy
A discussion of the various forms energy can take and how it can be transformed.
Introduction
Brandon Flowers is playing an electric guitar in a rock concert. He plucks the strings of the guitar
with skill, and the sounds of the music thrill the crowd.
The bright stage lights in the otherwise dark concert hall add to the excitement, although they make
it hot on stage. This scene represents energy in several different forms. Do you know what they are?
Comparing Forms of Energy
Energy, or the ability to do work, can exist in many different forms. The photo on the last slide
represents six of the eight different forms of energy that are described in this lesson.
Brandon Flowers gets the energy he needs to perform from chemical energy in food. He uses
mechanical energy to pluck the strings of the guitar.
The stage lights use electrical energy and give off both light energy and thermal energy, commonly
called heat. The guitar also uses electrical energy, and it produces sound energy when the guitarist
plucks the strings.
Mechanical Energy
Mechanical energy is the energy of an object that is moving or has the potential to move. It is the
sum of an object’s kinetic and potential energy.
The basketball has mechanical energy because it is moving. The arrow in the same figure has
mechanical energy because it has the potential to move due to the elasticity of the bow.
Chemical Energy
Energy is stored in the bonds between atoms that make up compounds. This energy is called
chemical energy, and it is a form of potential energy. If the bonds between atoms are broken, the
energy is released and can do work.
Wood in the fireplace in has chemical energy. The energy is released as thermal energy when the
wood burns.
People and many other living things meet their energy needs with chemical energy stored in food.
When food molecules are broken down, the energy is released and may be used to do work.
Electrical Energy
Electrons are negatively charged particles in atoms. Moving electrons have a form of kinetic energy
called electrical energy.
If you’ve ever experienced an electric outage, then you know how hard it is to get by without
electrical energy.
Most of the electrical energy we use is produced by power plants and arrives in our homes through
wires.
Nuclear Energy
The nuclei of atoms are held together by powerful forces. This gives them a tremendous amount of
stored energy, called nuclear energy.
The energy can be released and used to do work. This happens in nuclear power plants when nuclei
fission, or split apart. It also happens in the sun and other stars when nuclei fuse, or join together.
Some of the sun’s energy travels to Earth, where it warms the planet and provides the energy for
photosynthesis.
Thermal Energy
The atoms that make up matter are in constant motion, so they have kinetic energy. All that motion
gives matter thermal energy.
Thermal energy is defined as the total kinetic energy of all the atoms that make up an object. It
depends on how fast the atoms are moving and how many atoms the object has.
Therefore, an object with more mass has greater thermal energy than an object with less mass, even
if their individual atoms are moving at the same speed.
Electromagnetic Radiation
Energy that the sun and other stars release into space is called electromagnetic energy. This form of
energy travels through space as electrical and magnetic waves.
Electromagnetic energy is commonly called light. It includes visible light, as well as radio waves,
microwaves, and X rays.
Sound Energy
Drummers make music by hitting drumheads with drumsticks. This causes the drumheads to
vibrate.
The vibrations pass to surrounding air particles and then from one air particle to another in a wave
of energy called sound energy.
We hear sound when the sound waves reach our ears. Sound energy can travel through air, water,
and other substances, but not through empty space. That’s because the energy needs particles of
matter to pass it on.
How Energy Changes Form
Energy often changes from one form to another. For example, the mechanical energy of a moving
drumstick changes to sound energy when it strikes the drumhead and causes it to vibrate.
Any form of energy can change into any other form. Frequently, one form of energy changes into
two or more different forms.
For example, when wood burns, the wood’s chemical energy changes to both thermal energy and
light energy.
Energy is conserved in energy conversions. No energy is lost when energy changes form, although
some may be released as thermal energy due to friction.
For example, not all of the energy put into a steam turbine changes to electrical energy. Some
changes to thermal energy because of friction of the turning blades and other moving parts.
The more efficient a device is, the greater the percentage of usable energy it produces. Appliances
with an "Energy Star" label use energy efficiently and thereby reduce energy use.
Convection, Conduction, Radiation
The three primary ways energy is transferred from one location to another.
Convection
If a material is able to move, even if it moves very slowly, convection currents can form.
Convection occurs in many substances such as water, within the atmosphere, and even deep within
the Earth.
Without convection currents oceans would freeze, there would be no wind, and the surface of the
Earth would be as lifeless as the moon.
As molecules warm up they move faster due to increased kinetic energy.
As they move faster they take up more space allowing those molecules to rise above other colder,
slower moving molecules.
This phenomenon gives rise to the expression that “heat rises”.
Conduction
Heat is transferred through rapid collisions of atoms, which can only happen if the material is solid.
Heat flows from warmer to cooler places until all are the same temperature.
When you touch a surface and it feels warm, heat is transferring from the object to you through
conduction.
When you touch a surface and it feels cold, heat is transferring from you to the object.
Conduction only takes place through direct contact as the energy of one molecule moving is
transferred to another molecule it touches in a sort of collision.
If you leave a metal spoon in a pot of boiling water, the molecules of the spoon heat up due to
conduction.
Radiation
Radiation is the transfer of heat or energy through electromagnetic waves.
Electromagnetic waves do not require a medium to travel through such as a solid object or a fluid.
Electromagnetic waves can travel through space; EM waves from the sun warm the Earth.
The sun is the primary source of energy for the Earth.
Solar radiation becomes trapped within the Earth’s atmosphere and provides enormous amounts of
energy for different processes on Earth.
Solar radiation powers the water cycle, weather, ocean currents, and is the primary source of energy
for all life on Earth.