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 energy-the 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 EnergyElectrical 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 EnergyKinetic Energy of a PendulumKinetic 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 ForcesWhen 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. lever2. inclined plane3. screw4. wedge5. wheel and axle6. 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 Sciencewith

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 ScalesTwo 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.=24OCTo convert Celsius to Fahrenheit: °F = (9/5) (°C) + 32

Kelvin-SI unit for Temp. F.P=27K B.P.=37K