Download Physical Science: Unit 6: Energy

Unit 6: Energy
In this unit, you will explore what energy is and what
it does.
Lesson 1: Energy
In this lesson, you will learn how scientists define
energy. You will explore different forms of energy and
how they are a part of our everyday lives.
What Is Energy?
 Energy is the ability or capacity to do work.
 Work is using an applied force to make an
object move.
 Making changes in the physical world
 With energy, changes in the physical world
are possible.
 These can be a change in speed, a change in
direction, a change from cold to hot, and many other
kinds of changes.
Forms of Energy
We encounter many different kinds of energy every
day.
Some of the forms of energy are:
 mechanical
 chemical
 electrical
 sound
 light
 nuclear
Mechanical & Chemical
Energy
 Mechanical energy-the energy of motion
and position.
 It is the combination of two forms of energy–
potential energy-stored energy that is associated
with the position of an object and kinetic energythe energy of an object or substance because of its
motion.
 Chemical energy-form of potential energy
stored in chemical bond.
 For example, we can use natural gas to heat
homes and fuel cooking stoves.
Electrical & Nuclear Energy
Electrical energy is associated with electric charges.
 It can be sent along wires because of the way that
electrons move within the wire, exert forces, and
transfer energy.
 Electrical energy is used to light our homes and
schools and power our appliances.
Nuclear energy is energy that can be released by
changes in the nucleus of an atom.
 Nuclear energy is obtained when atoms of elements
like uranium and plutonium are split during a process
called nuclear fission-the splitting of the atoms
releases large amounts of nuclear energy.
 A nuclear power plant uses this nuclear energy to
generate electrical energy
Sound & Light Energy
Sound Energy-the energy produced when matter
vibrates
 When you speak, your vocal cords vibrate. You can
feel the vibrations when you touch your neck.
Light energy is a form of electromagnetic energy, the
vibration of electrically charged particles.
 It is the vibration of electrically charged particles that
send the light energy out into the space around
them.
Conservation of Energy
This law states that energy can neither be
created nor destroyed, but it can be
transformed.
 This means that energy can be transferred from
place to place and can also be converted
between the different forms of energy.
 But whether transformed or converted, the
amount of energy is always conserved; it
cannot be created or destroyed.
Energy Transformations
Some examples of energy transformations:
 Gasoline contains chemical energy. When it is burned, it
is transformed into heat energy and into mechanical
energy, which is needed to make vehicles move.
Although the form of energy changes, no energy is lost
or gained.
 Electrical energy is used to power radio speakers. The
speakers work by transforming electrical energy into
sound energy. Sound energy causes your ear drums to
vibrate and enables you to hear the music. Energy is not
gained or lost, but it changes form.
Sources of Energy
Energy resources can be categorized as either
renewable or nonrenewable.
 A renewable energy resource is one that can be
replaced. Ex. Sunlight, wind, moving water, and
wood
 A nonrenewable energy resource is one that cannot
be replaced. Ex. Oil, natural gas, coal, and uranium.
Measuring Energy
Energy can be measured using the SI unit called the
joule (J).
 One joule of energy is used when a force of one
newton is applied over a distance of one meter.
 While the newton-meter is the unit of
work, physicists found this term cumbersome, so
they decided to call one newton-meter a joule.
 1 joule (J) = 1 newton-meter (N •m)
Lesson 2: Work
In this lesson, you will explore the scientific meaning
of work.
Work
 In scientific terms, a force exerted on an object
does work when the object moves a distance in the
direction of the force.
 So, you do work by using an applied force to move
an object.
 When the force does work on the object, the object
moves in the same direction as the force.
Work Depends on Force and
Distance
 Even a great amount of force applied to an object
may not always do work.
 You may feel tired from trying to move an object,
but since it did not move, no work was done on it.
 Work involves both force and motion in the same
direction.
 It can be expressed by the following equation:
 W = Fd
work = force x distance
Power
 In scientific terms, power is the rate at which work
is done.
 Power measures how fast work happens, or how
quickly energy is used.
 Time does become a factor when calculating power.
 It can be calculated using the following equation:
 P = W/t
power = work/time
The Watt
 Power is measured in the SI unit of watts (W).
 One watt is equivalent to one J/s.
***Note that the symbol for watt (W) is similar to the symbol for work (W).
Both symbols use an uppercase W, but the symbol for work is italicized.
Make sure you don’t confuse the two when interpreting formulas or
completing calculations
Lesson 3: Kinetic Energy
In this lesson, you will explore kinetic energy and learn
how kinetic energy relates to moving objects, how it can
change, and how it can be calculated.
Energy in Motion
 Kinetic energy is the energy an object has
while it is in motion.
 All moving objects have kinetic energy.
 Kinetic energy enables moving objects to
perform work on other objects.
 Objects only have kinetic energy while
they are in motion. When an object stops
moving, its kinetic energy is zero.
Kinetic Energy Depends on
Mass & Speed
Mass:
 The amount of kinetic energy (KE) of a moving object
depends on its mass.
 A baseball has a greater mass than a ping-pong ball, so
greater kinetic energy.
Speed:
 Kinetic energy of a moving object also depends on how
fast it is going.
 The object that has greater speed will have greater
kinetic energy if they are both the same mass.
***Refer to K12 lesson for examples of both.
Kinetic Energy Equation
The kinetic energy of a moving object depends on both its mass and
speed.
This relationship is represented by the following equation:
 KE = ½mv2
kinetic energy = ½ (mass) (speed)2
 In this equation, m is used to represent mass (kg). The
symbol v is used to represent speed (m/s).
Therefore, v represents speed.
Step to solve for kinetic energy (Recall order of operations):
• square the quantity for speed
• multiply one half the mass
• multiply these two numbers together
• write the resulting answer in joules (J)
*** This may seem confusing at first, but remember that velocity without
direction is simply speed. In the equation for kinetic energy, direction is not a
factor.
Some Kinetic Energy
Examples
Changes in Kinetic Energy
Kinetic Energy of a Pendulum
Kinetic Energy of a Swing
Lesson 4: Potential
Energy
In this lesson, you will explore a form of energy called
potential energy. You will learn when objects have potential
energy, and how potential energy can become kinetic energy.
Energy of Position
 Potential Energy(PE)-the stored energy an
object has due to its position or shape.
 Objects that have potential energy are not
moving.
 Potential energy can either be elastic or
gravitational.
Elastic Potential Energy
 When a flexible object, such as a bow or a spring,
is bent, stretched, or compressed from its natural
shape, it stores elastic potential energy.
 Elastic objects tend to return to their natural shape
unless a force is acting on them.
 So when the shape of an elastic object is changed,
it stores elastic potential energy (EPE) before it
returns to its natural shape
Gravitational Potential Energy
 Objects can also store potential energy due to their
position.
 Objects take on gravitational potential
energy when they are lifted against the force of
gravity to a position where they have the potential
to fall.
 Gravitational potential energy (GPE) is a property
of elevated objects.
Gravitational Potential Energy
Equation
 The amount of GPE an object has depends on the
object’s weight (N) and height (m).
 The height of an object is measured in relation to a
reference point, such as the height above the floor.
 The formula for calculating gravitational potential
energy is PE = w x h, where potential energy =
(weight) x (height).
Converting Potential Energy to
Kinetic Energy &
Changes in Potential and Kinetic
Energy
 Objects at rest can have potential energy due to their
shape or position.
 A change in their shape or position can set them in
motion.
 Objects in motion have kinetic energy. Therefore,
potential energy can be converted into kinetic energy.
 For many systems, we can predict how potential energy
and kinetic energy will increase and decrease.
 K12 Ex. Roller Coaster
Lesson 7: Using a Lever
This lesson investigates a lever and will introduce you to
this section that examines work, energy, and machines.
Lever
A lever is a machine consisting
of a beam or rigid rod pivoted at
a fixed hinge, or fulcrum.
Lesson 8: Simple
Machines
In this lesson, you will learn what defines a machine in
physics. You will explore different types of simple
machines and how they are used to do work.
What Is a Machine?
 Work is applying a force to move an object over a
distance.
 A machine is any device that makes work easier…by
changing the strength or direction of a force.
 Machines do not decrease the amount of work that
needs to be done, they just make work easier by
changing the way it is done.
 Machines don’t just have buttons, knobs, and moving
parts…many everyday objects, such as rakes, bottle
openers, and ramps, are machines.
Machines Make Work Easier
 Simple Machine is a machine that makes
work easier when a single force is applied.
 Simple machines cannot do work by
themselves…energy be must provided to
make a simple machine do work.
Input and Output Forces
When you use a simple machine, you apply a force…called
the input force.
The force that the simple machine applies to an object is called
the output force.
The machine magnifies the input force, so that the resulting
output force is greater.
The work you apply to a simple machine is always equal to the
work the simple machine applies on an object.
 6 types of simple machines:
1. lever
2. inclined plane
3. screw
4. wedge
5. wheel and axle
6. pulley
Levers
 A lever is a simple machine that consists
of a rigid bar that pivots on a fixed point
called a fulcrum.
 Levers can change the direction of a force.
 Levers can also change the strength of a force
 K12 Ex. Seesaw, bottle cap, shovel, crowbar, and
a rake.
Inclined Plane
 An inclined plane is a flat, slanted surface, often
used to lift things…changing the strength of a
force.
 The longer an inclined plane, the less force is
required to move an object upward.
 With a longer ramp, the distance to the bus would
be longer because the ramp would extend out
further into the road.
Screw
 A screw is another type of simple machine.
 It is an inclined plane wrapped around a post.
 The inclined plane makes up the threads of the
screw.
 Imagine that you could unwind the threads of a
screw.
 The closer together the threads are, the longer the
inclined plane, and the smaller input is force
required to get the same output force.
Wedge
 A wedge is a two-sided inclined plane that can be
used to separate materials.
 A wedge changes the direction of a force.
 As with all inclined planes, wedges that are long
require less input force for the same output force
than wedges that are short.
 K12 EX. Ax, some knives, chisels, and teeth
Wheel and Axle
 A wheel and axle is a simple machine composed of
two attached circular objects that rotate in the
same direction. The larger object (the outside) is
the wheel, and the smaller object (the inside) is
the axle.
 This type of simple machines, the input force acts
on the axle, and the output force is exerted by the
wheel.
Pulley
 A pulley is a simple machine consisting of a
grooved wheel that holds a rope or a cable.
 Pulleys are often used to help lift objects.
 A pulley can also change the strength of a force.
 Pulleys that move with a load reduce the force
needed to lift the load as it is moved over a longer
distance.
Simple Machines Revisited:
1. A lever is a simple machine that consists of a rigid bar
that pivots on a fixed point called a fulcrum. Levers
change direction and strength of force.
2. An inclined plane is a flat, slanted surface, often used to
lift things. Changes the strength of force.
3. A screw is another type of simple machine. It is an
inclined plane wrapped around a post.
4. A wedge is a two-sided inclined plane that can be used
to separate materials
5. A wheel and axle is a simple machine composed of two
attached circular objects that rotate in the same direction.
6. A pulley is a simple machine consisting of a grooved
wheel that holds a rope or a cable as shown in the first
photo.
Welcome to Physical Science
with
Mrs. Brown
Lesson 9: Compound
Machines
In this lesson, you will explore how simple machines
work together in compound machines.
Simple vs. Compound
Machines
Machines make work easier by changing the strength or
direction of a force.
 A simple machine is a machine that makes work easier
when a single force is applied.
 Compound machines are made up of two or more simple
machines.
 Like all machines, they make work easier by changing the
strength or direction of a force.
 A compound machine may involve more than one
movement, and more than one force may act on a
compound machine.
 K12 Ex. The metal clasp of a zipper is made up of three
wedges
Combining Different Simple
Machines
Compound machines can also be a combination of
different types of simple machines.
A can opener combines three different types of simple
machines.
It is made up of a wedge, a wheel and axle, and two levers.
 Wedge: The blade is a wedge that cuts through the metal as the
can opener moves.
 Wheel and Axle: To move the can opener, you turn a wheel. The
wheel turns an axle. The axle turns gears that keep the can opener
gripped to the can and help it move. The gears also turn the wedge
that cuts the can.
 Levers: The arms of a can opener’s handle act as levers. When you
squeeze them over the lid of a can, a blade attaches to the lid’s
edge
Bike Parts are Simple
Machines
A bicycle also combines several different types of simple
machines to do work.
 Wheels and Axles: The wheels of a bicycle are wheels
and axles.
 Levers: The pedals are part of a lever. The gearshifts
and brake controls on the handlebars are levers, too.
 Pulley: The lever with the pedals turns a pulley that
holds the bicycle’s cha
Work, Force, and Distance in
Compound Machines
 Recall that work is represented by the equation W = Fd. In other
words, to complete the same amount of work, you can decrease the
amount of force you need to use by spreading it over a longer
distance. Or, you can decrease the amount of distance you need to
cover by increasing the amount of force you use. Let’s look at how
this relationship applies to compound machines.
 Suppose you use a pair of scissors, like the top photo, with long
blades and a short handle to cut an object. The force of the blades
coming together is spread along the blades’ length. Therefore, you
can make a long cut, but the force of the cut is weak. This tool is
good for cutting paper and fabric.
 Now suppose you use a pair of scissors, like the bottom photo, with
a short blade and a long handle to cut an object. The force of the
blades coming together is spread over a short distance. Therefore,
the cut is short, but the force is strong. This type of scissor is good
for cutting sheet metal and heavy materials
Lesson 11: Thermal
Energy
In this lesson, you will explore a form of energy
called thermal energy.
Review of Particles in Motion
 Everything is made of matter.
 Matter is made of small particles called atoms.
 Although the total mass of the block appears to be
stationary, the individual atoms are not.
 Each atom constantly moves, vibrating back and forth in
vibrational motion.
 The moving atoms have kinetic energy—the energy of
motion.
 As the atoms move, forces act between them that have
the potential to change their motion.
 So, the atoms also have potential energy—the stored
energy of position
Thermal Energy
 All matter has thermal energy-the internal energy.
 Thermal energy is the sum of the kinetic and
potential energy of all the particles in an object.
 The amount of thermal energy can be different in
different objects-objects of made of different
materials.
 Thermal energy depends partly on the size of an
object.
 Since thermal energy represents the total energy
of the particles in an object, at the same
temperature, the larger object will have more
thermal energy.
Thermal Energy and
Temperature
 Thermal energy also depends on the temperature
of an object.
 Suppose you have two objects of the same size at
different temperatures.
 Temperature affects the kinetic energy of particles.
 The particles in the warmer block will have more
kinetic energy and move faster than the particles
in the colder block.
 Thermal energy is the total of all the internal
energy in an object.
Thermal Energy and Heat
Thermal energy is transferred
between objects at different
temperatures.
The transfer of thermal energy is
called heat.
Heat always flows from a hotter
object to a colder one.
Heat and Thermal Equilibrium
 Thermal energy flows as heat from the warmer block to
the colder block.
 Energy transfers between the blocks until they reach the
same temperature and their particles move at the same
rate.
 When particles are at the same temperature and rate,
the blocks are in a state of thermal equilibrium.
 Thermal equilibrium means that the same amount of
thermal energy is transferred in each direction.
 So, at thermal equilibrium both objects will have the
same temperature.
Kinetic Theory of Heat
Theory that states that heat is the result
of the movement of particles in a system
3 ways these particles move:
 Conduction
 Convection
 Radiation
Conduction
 Conduction-the transfer of thermal energy between
two objects that are touching
 Conduction is the movement of thermal energy by
bodies or fluids that are in contact.
 When the two solids are in contact, heat moves
between them
Convection
 Convection is the transfer of energy by the movement of
a fluid, such as air or water.
 Particles in a fluid can move more freely than the
particles in a solid.
 The transfer of energy by convection does not require
direct contact between substances.
 Warmer water rises and cooler water sinks-called
convection currents.
 Winds and ocean currents are also convection currents that
transfer thermal energy from one place to another.
Radiation
 Radiation is the transfer of thermal energy by
electromagnetic waves.
 It can be transferred between objects or across empty
space.
 All objects emit electromagnetic radiation.
 Warmer objects emit more radiation than cooler ones.
 The sun transfers heat to the earth by radiation.
 A camp fire also transfers heat from the fire to warm your
body by radiation.
Lesson 12: Temperature
In this lesson, you will explore how scientists define
and measure temperature.
Temperature
 The temperature of an object is directly related to the
average kinetic energy of its atoms.
 The higher the average kinetic energy of an object, the
higher its temperature.
 When thermal energy flows into a substance as heat, it
causes particles to move faster-so, heat increases the
average kinetic energy of a substance.
 When average kinetic energy increases, temperature
increases.
How are Temperature and
Thermal Energy Different?
 Remember, thermal energy is the total kinetic and
potential energy of the particles in a substance.
 Temperature for any substance will increase when the
average kinetic energy of the particles in a substance
increases.
 A larger block has more mass and more atoms than the
smaller block, it also has more particles, it also has
greater total energy than the smaller block.
 So, the larger block has more thermal energy than the
smaller block.
 The temperature of the blocks is the same, but the
amount of thermal energy in each one is different.
Temperature and Expansion
 We have already established that when the temperature
of a substance increases, the kinetic energy of its
particles also increases. When kinetic energy increases,
the particles move faster. They also move farther apart
throughout a substance. When particles move farther
away from each other, their potential energy increases.
And, as a result of the particles spreading out, the
substance expands in size.
Temperature and Contraction
 An increase in temperature causes most objects to
expand or get larger. What do you think happens with a
decrease in temperature? A lower temperature will cause
most objects to contract. When the temperature of a
substance decreases, the kinetic energy of its particles
decreases. The particles move more slowly and move
closer together. As the particles move closer to each
other, the potential energy decreases.
In other words:
 Temperature vs. Thermal Energy
 thermal energy
 the total kinetic and potential energy of the particles in
a substance
 the more thermal energy in a substance, the more work
it can
 temperature
 any substance will increase when the average kinetic
energy of the particles in a substance increases
 when the temperature of a substance increases, the
kinetic energy of its particles also increases
 increase in temperature causes most objects to expand
or get larger
Thermometers
 The motion and position of particles in a substance will
change along with changes in temperature.
 Temperature changes can cause objects to expand or
contract.
 The first thermometer created to measure temperature
was based on this principle.
 One type of thermometer consists of a small volume of
alcohol encased in a thin glass tube. When the thermometer
is exposed to a hot substance, the alcohol in the
thermometer expands and rises up inside the tube. When
the thermometer comes into contact with a cold substance,
the alcohol contracts and sinks lower inside the tube. A
scale on the thermometer corresponds with the alcohol level
of the glass tube to indicate the temperature of the
substance.
Fahrenheit and Celsius Scales
Two common temperature scales are Fahrenheit and
Celsius.
 Most countries use the Celsius scale to measure
temperature.
 With this scale, the freezing point of water is set at 0°, and
the boiling point is set at 100°. A comfortable room
temperature in Celsius is about 24°.
 In some countries, including the United States, the
Fahrenheit scale is used to indicate temperature.
 With this scale, the freezing point of water is set at 32°, and
the boiling point is set at 212°. A comfortable room
temperature in Fahrenheit is about 75°.
Converting Fahrenheit and
Celsius
You can use the following equations to convert
Fahrenheit and Celsius:
 To convert Fahrenheit to Celsius: °C = (5/9)
(°F – 32)
 To convert Celsius to Fahrenheit: °F = (9/5) (°C)
+ 32
Kelvin Scale
 Remember, temperature relates to the average kinetic
energy of the particles in a substance.
 After studying the motion of molecules in gases, scientists
developed the Kelvin scale to express temperature in
relation to kinetic energy.
 One unit on the Kelvin scale, called a kelvin (K), is the SI
unit of temperature.
 The Kelvin system is based on the temperature at which the
motion of particles is at its lowest possible level.
 At this temperature, the kinetic energy of the particles is as
small as it can be.
 The lowest temperature that a molecule could possibly be is
called absolute zero.
 The value of absolute zero is 0 K or –273°C
Temperature Scales
Temperature Scales:
(Boiling Point-B.P., Freezing Point-F.P., Room Temperature-R.T.)
 Fahrenheit-used in the U.S. F.P.=32OF B.P.=212OF R.T.=75OF
 To convert Fahrenheit to Celsius: °C = (5/9) (°F – 32)
 Celsius-most common in the world.
F.P.=0OC B.P.=100OC R.T.=24OC
To convert Celsius to Fahrenheit: °F = (9/5) (°C) + 32
 Kelvin-SI unit for Temp. F.P=27K B.P.=37K