what is energy? what is the relationship between energy and work? compare kinetic and potential...

What is Energy?

What is the relationship between energy and work?

Compare kinetic and potential energy

What are the different types of energy?

What is energy?

Energy is the ability to do work.

Great, but what is work?

Work is done when a force (caused by energy) causes an object to move.

Work = Force x distance

Energy / Work

Energy is needed to push a box across the floor. The box moving across the floor is an example of work.

Energy is needed to hit a home run. The ball flying over the fence is an example of work.

Two Basic Types of Energy

Potential Energy = the energy of an object due to its position, shape, or condition

Kinetic Energy = the energy of an object due to the object’s motion

Potential Energy Not all energy has to do with motion.

Potential Energy is the energy an object has because of its position, shape, or condition.

Objects with potential energy have the potential, or ability, to do work.

Potential Energy Preview

We will learn about three kinds of Potential Energy

1. Elastic Potential Energy

2. Chemical Potential Energy

3. Gravitational Potential Energy

Elastic Potential Energy The bow has energy because work

has been done to change its shape.

The energy of that work is turned into potential energy.

When the arrow is released the potential energy of the bow and string will be transferred to the arrow, sending it flying through the air.

Elastic Potential Energy

Compressed, or squished, springs also have potential energy.

A spring has energy because work has been done to change its shape.

Just like the bow, the energy of that work is turned into potential energy.

Elastic Potential Energy

What about rubber bands and other things that stretch?

Elastic Potential Energy

How do we “release” the potential energy stored in springs?

Chemical Energy

Chemical Energy is the potential energy stored in substances.

Calories = the chemical energy of food Batteries also have chemical energy It all depends upon the position and

arrangement of the atoms in a compound.

Chemical Potential Energy A battery has potential energy

due to its condition.

Potential Energy is stored in the chemicals within the battery.

A fully charged battery has the potential to do work.

Chemical Potential Energy

Chemical Potential Energy can be found in food.

Calories!

Chemical Energy (cont’d)

Which type of food has the highest chemical potential energy (calories)?

Gravitational Potential Energy When someone pushes you on a

swing, you and the swing gain potential energy because work has been done to change your position.

You will have the most potential energy at the top, right before you begin your arc downward.

Think about swinging. When will you have the most kinetic energy?

Gravitational Potential Energy

When you lift an object, you do work on it. You use a force that is against the force of

gravity. When you do this you transfer energy to the

object and give the object Gravitational Potential Energy.

The amount of Gravitational Potential Energy an object has depends on the objects weight and height above the ground.

Gravitational Potential Energy

Books on a shelf have Gravitational Potential Energy.

Which books have the most Gravitational Potential Energy? Why?

Gravitational Potential Energy

A man and his cell phone are on a ledge outside a very tall building.

Which object (the man or his cell phone) has the most Gravitational Potential Energy? Why?

How do we calculate Gravitational Potential Energy?

GPE = Weight x Height

Measure Weight in Newtons (N)

Measure Height in meters (m)

The unit for Gravitational Potential Energy = Newton meters (Nm) or Joules (J)

Calculate the Gravitational Potential Energy

GPE = Weight x Height

Book #1 weighs 25 N on a shelf that is 2 meters off of the ground.

Book #2 weighs 25 N and is on a shelf only 1 meter off of the ground.

Which book has the most GPE?

Calculate the Gravitational Potential Energy GPE = Weight x Height

Man weighs 300 N on a ledge that is 200 meters off of the ground.

Cell Phone weighs 15 N and is on the same ledge.

Which object has the most GPE?

Practice Calculating GPE

GPE = Weight x Height

Tools: Metric tape measure, spring scale (be sure to use the Newton scale), calculator

Units! Units! Units! ~ The units for GPE are Newton meters (Nm) or Joules (J)

Potential Energy Review

We learned about three kinds of Potential Energy

1. Elastic Potential Energy

2. Chemical Potential Energy

3. Gravitational Potential Energy

Kinetic Energy Preview

Kinetic Energy is the energy of motion or energy in use

Any matter in motion has Kinetic Energy There are many forms of Kinetic Energy Some forms include: light (radiant),

thermal (heat), sound (acoustic), electrical, and mechanical

Thermal Energy

All matter is made up of atoms Atoms are in constant motion Thermal energy (heat) is all of the kinetic

energy due to the random motion of atoms Thermal energy also depends upon the

amount of atoms that are moving

Solids The atoms in an

ice cube vibrate in fixed positions and do not have a lot of kinetic energy.

Liquids Atoms of water

in a lake can move more freely and have more kinetic energy than atoms in ice do.

Gas The atoms of

water in steam move rapidly, so they have more energy than the particles in liquid water or ice do.

Thermal Energy (cont’d)

Thermal energy depends upon the amount of atoms that are moving.

Consider, a cup of tea and the water in a bath tub.

Both are the same temperature.

Which has more thermal energy?

? ? ? ? ? ? ?

The water in the bathtub has more thermal energy.

Why?Simply because it has more water

molecules.

Conduction

Conduction is the transfer of energy through matter from particle to particle.

It is the transfer and distribution of heat energy from atom to atom within a substance. Conduction is most effective in solids-but it can happen in fluids.

Conduction (cont’d)

For example, a spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon.

Conduction (cont’d)

Have you ever noticed that metals tend to feel cold? Believe it or not, they are not colder! They only feel colder because they

conduct heat away from your hand. You perceive the heat that is leaving your

hand as cold.

Conduction (cont’d)

Some items are conductors, they conduct heat well. Example: metal

Some items are insulators, they DO NOT conduct heat well. Examples: fabric, wood, wool, and some plastic

Think about it . . .

What do we use a “cooler” for?

What do we use a coffee mug for?

Differences / Similarities?

Convection

Convection is the transfer of heat by the actual movement of the warmed matter.

Heat leaves the coffee cup as the currents of steam and air rise.

Convection is the transfer of heat energy in a gas or liquid by movement of currents.

Convection (cont’d)

Convection is responsible for making

macaroni rise and fall in a pot of heated water.

The warmer portions of the water are less dense and therefore, they rise.

Meanwhile, the cooler portions of the water fall because they are denser.

Mechanical Kinetic Energy

Kinetic Energy = the energy of an object due to the object’s motion

All moving objects have kinetic energy

Kinetic Energy depends on Mass and Speed

Mechanical Kinetic Energy (cont’d)

KE = mass x speed x speed divided by 2

The greater the mass of a moving object, the more Kinetic Energy it has.

The faster something is moving, the more Kinetic Energy it has, also.

Mechanical Kinetic Energy Which animal has the

bigger mass?

Which animal is able to move faster?

Which animal has the greatest KE?

KE = mass x speed2

2

Calculate the Mechanical Kinetic Energy (KE)

KE = mass x speed2

2

Mass = 0.2 kg Speed = 2 meters/sec

KE = 0.4 J

Mechanical Kinetic Energy KE = mass x speed2

2

Mass = 4000 kg Speed = 2 meters/sec(Note that the elephant is

going the same speed as the mouse.)

KE = 8000 J

What effect does an increase of speed have on Mechanical Kinetic Energy?

The green and yellow cars have the same mass (1,200 kg)

The green car is traveling at a speed of 20 m/sec

The yellow car is traveling at a speed of 30 m/sec

Calculate their Kinetic Energies

KE = mass x speed2

2

Which car has the most KE? Green car’s KE = 240,000 J Yellow car’s KE = 540,000 J

Speed has a greater effect on KE than mass because in the equation speed is squared.

In other words, the faster an object is going . . . the more KE is has.

Practice Calculating KE

Use Joules (J) as the unit for Kinetic Energy

Tools: meter tape, stop watch, scale, calculator

KE = mass x speed2

2

Electrical Energy Electrical Energy is

the energy of moving electrons.

Electricity is the flow of electrical power or charge.

Electrical Energy (cont’d)

It is a secondary energy source which means that we get it from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources.

Electrical Energy (cont’d) The energy

sources we use to make electricity can be renewable or non-renewable, but electricity itself is neither renewable or non-renewable.

Two types of electricity: Static and Current

Static electricity is usually caused when certain materials are rubbed against each other, like wool on plastic or the soles of your shoes on the carpet.

It is the attraction of two objects because one has a positive charge and the other has a negative charge.

Two types of electricity: Static and Current

The flow of The flow of electrons is electrons is called an electric called an electric currentcurrent

Look familiar?

Some items are conductors, they conduct electricity well. Example: metal

Some items are insulators, they DO NOT conduct electricity well. Examples: fabric, wool, wool, and some plastic

Semiconductors Some items are

semiconductors.

The ability of a semiconductor to conduct electrictiy is between the ability of a conductor and an insulator.

A dimmer switch is a semiconductor.

Resistors

Resistors resist the flow of electrons. They are really good at transforming

electrical energy into other forms of kinetic energy (sound, light, heat).

We find resistors in radios,

light bulbs, and ovens.

Sound or Acoustic Energy

Sound Energy is caused by an object’s vibration.

Sound is a type of energy made by vibrations. When any object vibrates, it causes movement

in the air particles. These particles bump into the particles close to

them, which makes them vibrate too causing them to bump into more air particles.

This movement, called sound waves, keeps going until they run out of energy.

If your ear is within range of the vibrations, you hear the sound.

Sound Energy (cont’d)

Picture a stone thrown into a still body of water.

The rings of waves expand indefinitely.

The same is true with sound.

Sound Energy (cont’d)

Irregular repeating sound waves create noise

While regular repeating waves produce musical notes

Sound Energy (cont’d)

When the vibrations are fast, you hear a high note.

When the vibrations are slow, it creates a low note.

Playing the Guitar

Stretching a guitar string, stores potential energy in the string

Letting it go causes the potential energy to be transformed into kinetic energy

This makes the string vibrate

Playing the Guitar (cont’d)

The vibrating string transfers some of this energy to the surrounding air

The vibrating air travels to your ear

When this energy reaches your ear, you hear the guitar

Radiation

Electromagnetic waves that directly

transport ENERGY through space. Sunlight is a form of radiation that is radiated

through space to our planet. The sun transfers heat through 93 million miles

of space. The energy travels through nothingness! No

matter required!

Radiant Energy

Radiant energy is energy in the form of electromagnetic waves.

Radiant energy can travel through a vacuum.

Examples of radiant energy = visible light, infrared light, microwaves, radio waves, ultra violet light, X-rays, and gamma rays.

Light Energy

Light energy is produced by the vibrations of electrically charged particles.

Unlike sound energy, the vibrations that transmit light energy do not need to be carried through matter.

Light Energy (cont’d)

In fact, light energy can move through a vacuum (an area with no matter).

Also known as visible light energy.

Nuclear Energy

Nuclear Energy is the energy that comes from changes in the nucleus of an atom.

A lot of potential energy is stored in the nucleus of atoms

When two nuclei join together, or when a nucleus splits apart, a lot of energy is released. This is nuclear energy.

Nuclear Energy (cont’d) Fusion = The joining of two

nuclei. This happens on the sun.

Fission = The splitting of a nuclei. Fission is used in nuclear power plants to generate electrical energy.

How are Kinetic and Potential Energy

Related?

Law of Conservation of Energy

Energy can not be created or destroyed It can be transformed, or changed, from one

form to another Kinetic Energy can be transformed into Potential

Energy or other types of Kinetic Energy, and vise versa. This can and does happen many times.

The total amount of energy doesn’t change.

Dynamic Mechanical Energy Imagine a juggler Sometime the objects

have a lot of kinetic energy

Sometimes the objects have a lot of potential energy

A book on a shelf ledge has potential energy.

It has stored the energy that it took to lift it to the shelf.

If the book is bumped and it falls, the potential energy changes to the kinetic energy of motion.

When does the book have the most potential energy?

When does the book have the most kinetic energy?

Forms of Kinetic Energy

Mechanical

Thermal Energy or Heat Energy

Electric Energy

Sound or Acoustic Energy

Light or Radiant Energy

Nuclear Energy

ReviewEnergy is the ability to do work

Work is the transfer of energy

Energy cannot be created or destroyed, but it can change form

Potential Energy Review

We learned about three kinds of Potential Energy

1. Elastic Potential Energy

2. Chemical Potential Energy

3. Gravitational Potential Energy

Review (cont’d) Potential Energy is energy of position,

shape, or condition

Gravitational Potential Energy depends on weight and height

GPE = Weight (N) x Height (m)

Review (cont’d)

Kinetic Energy is energy of motion

It depends on speed and mass

Review (cont’d) Energy exists in many forms

Each form has its own characteristics

Some of the forms of kinetic energy we learned about were: mechanical, thermal, electrical, sound or acoustic, light or radiant, and nuclear energy