Download Review Unit 5 Properties of Energy

Unit 5 Properties of Energy
Lessons 1, 2, 3, & 4
When something is capable of causing change, it has energy. Energy is the ability to cause
change. Energy is measured in units called joules (J). When you turn on your radio or MP3 player, change
happens when sound comes through the headphones or speakers. Some of the forms that energy can
take include light, heat, sound, electricity, chemical, and nuclear energy.
The Sun generates light and heat, both of which are used by organisms on Earth. You use
mechanical energy when you ride a bicycle or a skateboard. When you surf the internet or listen to the
radio, you are using electrical energy. Your body relies on the chemical energy it got from the vegetables,
bread, or meat you ate.
All forms of energy can be classified as potential or kinetic energy. Kinetic energy is the energy a
moving object has because of its motion. All moving objects have kinetic energy. The faster an object is
moving, the more kinetic energy it has. For example, a speeding train has more kinetic energy than a
person riding a bike. There are different forms of kinetic energy. Electricity is related to the kinetic energy
of electrons. Sound is the kinetic energy of particles as they move in waves. Recall that matter is made up
of particles that are constantly in motion. These particles have kinetic energy. Thermal energy is the
motion of these particles. You feel this energy as heat.
A rock at the top of a hill has stored energy. When it rolls down, a change occurs. At the top of the
hill, the rock has energy because of its position above the valley below. Energy that is stored is called
potential energy because it has the potential to cause change. The rock at the top of the hill keeps the
stored energy because of its height. If it rolls down the hill, that stored energy becomes the energy of
motion.
Think of a roller coaster, at the top of the hill, the roller coaster has its highest level of potential
energy. Because it is not moving fast at that point, the kinetic energy of the coaster is relatively low. Then
the coaster races down the hill. As its distance from Earth’s surface decreases, its potential energy
decreases. However, the whole time it is moving down the hill, the coaster is accelerating because its
kinetic energy is increasing.
When the roller coaster begins to climb the second hill, the cycle repeats itself. Kinetic energy
starts to decrease as the coaster slows down. At the same time, the roller coaster is climbing a hill, so its
potential energy is increasing. Throughout the ride, the roller coaster might have both kinetic and potential
energy. Mechanical energy is the combination of the potential and kinetic energy that something has.
Windup toys are another example of objects that may have mechanical energy. When you turn the key on
a windup toy, you tighten a spring. This gives the toy potential energy. The toy moves as the spring
unwinds. When the toy is moving, it has kinetic energy. The spring is still partly wound up, so the toy also
has potential energy. An object’s mechanical energy is the sum of its kinetic and its potential energy.
There are different types of potential energy. Plants make their own food. They do this by
harnessing energy from the Sun and storing it in their tissues. All food contains energy stored in the
chemical bonds between atoms. Energy stored in chemical bonds is called chemical potential energy.
When you eat food, your body breaks it down into smaller and smaller pieces, eventually breaking some
of the bonds between the atoms. This process releases the energy that is stored there. Gasoline is
another example. When you start a fire or burn fuel, the bonds between atoms are being broken, and the
resulting heat is a sign that energy is being released.
When you stretch or compress a spring, you are storing another form of potential energy called
elastic potential energy. Elastic potential energy is energy stored in objects that are stretched or
compressed. Gravitational potential energy is energy stored by objects due to their position above Earth’s
surface. The GPE of an object depends on the object’s mass and height above the ground.
Energy can change from a potential to a kinetic form. If you turn on a television, electrical energy
changes to light and sound energy. If you turn on a hair dryer, electrical energy changes to thermal
energy. If you turn on a blender, electrical energy changes to mechanical energy. If you play a musical
instrument, mechanical or electrical energy changes to sound energy. Batteries contain stored chemical
energy. Reactions inside a battery change chemical potential energy to electrical energy. This electrical
energy can then be changed to various other forms of energy, such as light or heat. A stereo changes
electrical energy to mechanical energy. This mechanical energy vibrates the stereo speakers, which
causes the air molecules to move, producing sound. When you walk or jog, your muscles change the
chemical energy from the food you ate into mechanical energy.
Although energy constantly changes from one form to another, it is never created or destroyed.
This is known as the laws of conservation of energy. The law of conservation of energy cannot be broken.
When energy changes form or causes change, it will often produce waste heat. The energy that is lost
due to friction becomes thermal energy.
What are waves? A wave is a disturbance that transfers energy from one point to another. Some
waves, such as light waves, can travel through empty space. Other kinds, such as sound waves, must
travel through a medium, or substance, in order to transfer energy. A medium can be a solid, liquid, or a
gas. The movement of particles by a wave is called vibration.
When a transverse wave travels through a medium, matter moves up and down as the wave
travels through it. When a compressional wave travels, matter moves back and forth as the wave travels
through it. The vibration of a spring’s coils produces a compression an area where particles are pushed
together. Behind the compression is a rarefaction, an area where particles are spread apart. The crest of
a transverse wave is highest point. In a compressional wave, the crest is the point of greatest
compression – the area where particles are closest together. Waves have troughs. The trough of a
transverse wave is its lowest point. In a compressional wave, the trough is the point of greatest
rarefaction- the area where particles are farthest apart.
Wavelength is the distance between wave crests or troughs in a transverse wave. The wavelength
of a compressional wave is the distance from one compression to the next compression or from one
rarefaction to the next rarefaction. Amplitude, the height of the wave from its trough or crest to its
midpoint, is a measure of the waves’ intensity. In the ocean, a wave’s amplitude increases as it nears the
shore. Frequency is a measure of how many wave crests or troughs pass a given point in a unit of time.
High-frequency waves have shorter wavelengths and transfer greater energy. Frequency is measured in
hertz (Hz), the number of waves per second. Hertz means “cycles per second” with respect to frequency.
A sound wave is a compressional wave produced by vibrations in matter. Molecules in the medium
move back and forth, pushing nearby molecules. Sound waves cannot travel through empty space. When
you look in a mirror, light waves bounce off the mirror into your eyes and enable you to see your image.
Sound waves also reflect off of objects. Reflection refers to how waves bounce off of objects and change
their direction of travel. Have you ever heard an echo? An echo is a reflected sound wave. Hard surfaces
easily reflect sound waves. Soft surfaces absorb sound waves. Absorption is the transfer of energy when
a wave disappears into a surface.
How does light travel? Light is a form of energy that travels in waves. Light waves spread out as
they move away from a source. Light travels in straight lines called rays. Light waves can travel through
empty space, without needing a solid, liquid, or a gas medium.
Transparent matter allows light to pass through with almost no disturbance. Behind transparent
materials, objects look clear and crisp, even if the transparent materials change the color of the light. A
lens, such as the one found in either side of a pair of eyeglasses, is a piece of transparent material with at
least one curved surface. When light rays strike matter that is translucent, some light passes through, and
some is either blocked or bent in different directions. Objects viewed through translucent materials do not
look clear or crisp; they appear blurred. Light does not pass through matter that is opaque. Opaque matter
reflects or absorbs all light. The light that is absorbed is converted to heat energy. An opaque object casts
a shadow when it is in front of a light source. A shadow is a dark area produced by an opaque object
blocking the passage of light. Light always moves in straight lines, so when light is blocked by the opaque
object, a shadow forms that is similar in shape to the object that produce it.
The angle between an incoming light ray and a surface is equal to the angle between the reflected
light ray and the surface. This is called the law of reflection. The bending of a wave as it moves from one
medium into another is called refraction. Refraction occurs when the speed of a wave changes as it
passes from one substance to another.
A wave that can travel through empty space or through matter is called an electromagnetic wave.
These waves radiate, or spread out, in all direction from a source. The range of electromagnetic waves
forms the electromagnetic spectrum. The spectrum is arranged from long waves, with the lowest amount
of energy, to short waves, with the highest amount of energy. The spectrum consists of radio waves,
microwaves, infrared waves, visible light, ultraviolet rays, X-rays, and gamma rays. Even though they
have different names, they travel at the same speed in empty space – the speed of light.
Radio waves have the lowest frequencies and the least energy of the waves in the electromagnetic
spectrum. Television and AM and FM radio signals are carried by radio waves. Microwaves are a type of
radio wave. Microwaves are used to transmit some cell phone calls. Microwaves are used to heat food.
Infrared waves are electromagnetic waves given off by an object at room temperature. The infrared
detectors can detect objects that are warmer or cooler than room temperature. Visible light is waves that
your eyes can see. Visible light from the Sun comes to Earth as white light. White light contains the colors
of the rainbow. A prism can separate white light into ROY G. BIV, red, orange, yellow, green, blue, indigo,
and violet. When sunlight passes through a prism, refraction occurs twice. Violet light has the shortest
wavelength and is bent the most. Red light has the longest wavelength and is bent the least. Each color
has a different wavelength and is refracted at different angles. Sunlight striking an object may be
reflected, refracted, or absorbed. When light strikes an object, the object reflects some colors but absorbs
other colors. The absorbed colors are missing in the reflected light. The reflected colors mix to produce
the color of the object. The leaf looks green because it reflects green light. It absorbs all other colors. The
light that is absorbed is used in photosynthesis. An object that reflects all visible light appears white. An
object that absorbs all visible light appears black.
Ultraviolet radiation has a higher frequency than visible light and has even shorter wavelengths.
Ultraviolet radiation also carries more energy than visible light. The energy carried by ultraviolet waves
can be enough to damage cells. Too much exposure to the Sun’s rays can cause sunburns. To heal
ultraviolet damaged skin, extra blood is sent to the skin. This is why sunburns turn the skin red. Repeated
sunburns can cause skin cancer. Some lotions can help block the Sun’s harmful rays. The atmosphere is
transparent to radio waves and visible light, partially transparent to infrared waves and ultraviolet
radiation. Higher-energy waves of x-rays and gamma rays are absorbed in the Earth’s atmosphere.
X-rays can destroy living cells. Unlike ultraviolet rays that can penetrate and damage skin cells, xrays penetrate much deeper into the body and can damage muscles and organs. The radiation received
from getting one medical or dental x-ray is not harmful. However, too much exposure to numerous x-rays
can be dangerous. Lead shields or aprons are used to protect the parts of the patient’s body that are not
receiving x-rays.
Gamma rays have the shortest wavelengths, highest frequencies, and greatest energy of all waves of the
electromagnetic spectrum. They contain so much energy that they can pass through several centimeters
of lead.
Questions (Copy the question & write the answer on a separate sheet of paper)
1. What is energy?
2. What are the 7 forms of energy?
3. Give an example of each.
4. Give two examples of energy transformations. Example: Radio – electrical energy to sound energy
5. Why is the first hill on a roller coaster the tallest?
6. Why does a roller coaster need a chain to lift it to the top of the first hill but not the second hill?
7. Which energy is associated with the movement of electrons from one place to another?
8. What is a wave?
9. What is the difference between wavelength and amplitude?
10. How are light energy and sound energy similar? How are they different?
11. What kind of energy from the Sun can cause a sunburn?
12. What is the difference between red light wave and violet light wave?
13. How do sound waves travel?
14. Which part of the electromagnetic spectrum has the shortest wavelength? The highest frequency?
15. What is the relationship between the frequency & wavelength?
16. What is the difference between translucent, transparent, & opaque?
17. What is the difference between refraction & reflection?
18. Explain how sound waves travel through different mediums.
19. Explain why a shirt is red, a leaf is green, dry erase board is white, and your RMS sweat shirt is black.
20. Explain how potential & kinetic energy are changing on a roller coaster ride.
21. Draw and label the electromagnetic spectrum.
Answers:
1. Energy is the ability to cause change or do work.
2. The 7 forms of energy are mechanical, radiant (light),
sound, chemical, heat (thermal), electrical, and nuclear.
3. An example of each of the 7 forms of energy are:
mechanical: wind-up toy, radiant (light): the Sun or light
bulb, sound: vibrations of a stereo speaker, chemical:
food or battery, heat (thermal): hot water in a radiator,
electrical: a generator or battery, and nuclear: the Sun
or radioactive material.
4. Two examples of energy transformations are guitar
vibrations: mechanical to sound energy. Photosynthesis:
light to chemical energy, flashlight: chemical to
electrical to light & heat
5. The first hill of the roller coaster is the highest to build up the greatest amount of
potential energy.
6. The roller coaster has no kinetic or potential energy to
move to the top of the first hill, so it has to be pulled up
with a chain. However, the kinetic energy it gains as it
moves down the first hill is large enough to carry it up
the second hill.
7. electricity is the energy associated with the movement
of electrons from one place to another.
8. A wave is a disturbance that transfers energy from one
point to another.
9. Wavelength is the distance between wave crests or
troughs in a transverse wave. Or the distance between
compression or rarefaction in a compressional wave.
Amplitude is half the height of the wave or height from
crest or trough to midpoint.
10. Light and sound energy both travel as waves.
Light can travel through space, whereas sound requires
a solid, liquid, or gas medium.
11. Ultraviolet radiation is energy from the Sun that can
cause a sunburn.
12. The difference between red light wave and violet
light wave is red light has less energy/lower frequency
and violet light wave has higher energy/higher frequency.
13. Sound waves travel outward in all directions as a
compressional wave moving through matter.
14. Gamma rays have the shortest wavelength and the
highest frequency on the electromagnetic spectrum.
15. If the frequency increases the wavelength decreases.
16. Translucent allows some light to pass but object
appear blurry, transparent allows all light to pass and
objects appear crisp and clear, opaque allows no light
to pass through and objects cast a shadow.
17. Reflection refers to how waves bounce off objects
and change their direction of travel. Refraction is the
bending of a wave as it moves from medium to another.
Like a straw in a glass of water. The speed of the wave
travels slower in water than in air.
18. Sound waves travel fastest through solids, slower
through liquids, and slowest through gas.
19. Light waves carry the colors of the rainbow.
The shirt is red because red light is reflected and
all other colors are absorbed, the leaves are green
for the same reason. The board is white because
all visible light colors are reflected and your sweat
shirt is black because all the colors of white light is
absorbed.
20. The first hill on a roller coaster is the highest to
build up the most potential energy. As the roller coaster
goes down the potential energy decreases as the
kinetic energy increases. At the bottom of the hill the
kinetic energy is the highest and the potential energy is
the lowest. As the roller coaster starts to go up again.
The potential energy decreases as the kinetic energy increases.
21.