chapter 9 energy: forms and changes section 1: what is energy?
TRANSCRIPT
Chapter 9Chapter 9
Energy: Forms and ChangesEnergy: Forms and Changes
Section 1: What is Energy?
Essential questions
What is the relationship between energy and work?
What is the difference between kinetic and potential energy?
Identify the different forms of energy and tell about each one.
Nature of Energy
Energy is all around you!You can hear energy as sound.You can see energy as light.And you can feel it as wind.
Nature of Energy
You use energy when you: hit a softball. lift your book
bag. compress a
spring.
Nature of Energy
Living organisms need energy for growth and
movement.
Nature of Energy
Energy is involved when: a bird flies. a bomb explodes. rain falls from the
sky. electricity flows in
a wire.
Nature of Energy
What is energy that it can be involved in so many different activities?Energy can be defined as the
ability to do work.If an object or organism does
work (exerts a force over a distance to move an object) the object or organism uses energy.
Nature of Energy
Because of the direct connection between energy and work, energy is measured in the same unit as work: joules (J).
In addition to using energy to do work, objects gain energy because work is being done on them.
States of Energy: Kinetic and Potential Energy
Kinetic Energy is the energy of motion.
Potential Energy is stored energy.
Mechanical energy is potential energy + kinetic energy.
Kinetic Energy
The energy of motion is called kinetic energy.
The faster an object moves, the more kinetic energy it has.
The greater the mass of a moving object, the more kinetic energy it has.
Kinetic energy depends on both mass and velocity.
Kinetic Energy Kinetic Energy = mass times velocity
squared divided by two
K.E. = mass x velocity 2
What has a greater affect on kinetic energy, mass or velocity? Why?
Potential Energy
Potential Energy is stored energy. Stored chemically in fuel, the nucleus of
atom, and in foods. Or stored because of the work done on
it: Stretching a rubber band. Winding a watch. Pulling back on a bow’s arrow. Lifting a brick high in the air.
Types of Potential Energy
There are 3 types of Potential Energy Gravitational Elastic Chemical
Gravitational Potential Energy
Potential energy that is dependent on height is called gravitational potential energy.
Gravitational Potential Energy
A waterfall, a suspension bridge, and a falling snowflake all have gravitational potential energy.
Gravitational Potential Energy
If you stand on a 3-meter diving board, you have 3 times the G.P.E, than you had on a 1-meter diving board.
Gravitational Potential Energy
“The bigger they are the harder they fall” is not just a saying. It’s true. Objects with more mass have greater G.P.E.
The formula to find G.P.E. isG.P.E. = Weight X Height.
Elastic Potential Energy
Energy that is stored due to being stretched or compressed is called elastic potential energy.
Chemical Energy
Chemical Energy is required to bond atoms together.
And when bonds are broken, energy is released.
Chemical energy is a form of potential energy because it depends on the position and arrangement of atoms.
Chemical Energy
Fuel and food are forms of stored chemical energy.
Mechanical Energy
When work is done to an object, it acquires energy. The energy it acquires is known as mechanical energy.
Mechanical energy = potential energy + kinetic energy
Mechanical Energy
When you kick a football, you give mechanical energy to the football to make it move.
Mechanical Energy
When you throw a bowling ball, you give it energy. When that bowling ball hits the pins, some of the energy is transferred to the pins (transfer of momentum).
Forms of Energy
The other main forms of energy are:Thermal (heat)ElectricalSoundLightNuclear
Thermal Energy
The internal motion of the atoms is called thermal energy, because moving particles produce heat.
Heat energy can be produced by friction. Faster the particles move, the more kinetic energy and the more heat they produce.
Heat energy causes changes in temperature and phase of any form of matter.
Electrical Energy
Power lines carry electromagnetic energy into your home in the form of electricity.
Electrical energy is the energy of moving electrons.
Electrons are negatively charged particles of atoms.
Sound Energy
Sound energy is caused by a vibrating object.
The vibrations are transferred through the air to your ear and your ear deciphers it.
Light Energy
Light is a form of electromagnetic energy.
Light energy is produced by the vibrations of electrically charged particles.
Each color of light (Roy G BIV) represents a different amount of electromagnetic energy.
Electromagnetic Energy is also carried by X-rays, radio waves, and laser light.
Nuclear Energy
The nucleus of an atom is the source of nuclear energy.
Nuclear Energy
When the nucleus splits (fission), nuclear energy is released in the form of heat energy and light energy. Power plants use fission to generate electrical energy.
Nuclear energy is also released when nuclei collide at high speeds and join (fusion).
Nuclear Energy
•The sun’s energy is produced from a nuclear fusion reaction in which hydrogen nuclei fuse to form helium nuclei.
•The sun’s heat and light come from fusion.
Nuclear Energy
Nuclear energy is the most concentrated form of energy.
Chapter 9Chapter 9
Energy: Forms and ChangesEnergy: Forms and Changes
Section 2: Energy
Conversions
Essential Questions
What is an energy conversion? What are some examples of energy
conversion for the different forms of energy?
How can energy conversions make energy useful?
What is the role of machines in energy conversions?
Energy Conversion
Energy can be changed from one form to another. These changes are called energy conversions.
Energy conversions
All forms of energy can be converted into other forms. The sun’s energy through solar cells
can be converted directly into electricity.
Green plants convert the sun’s energy (electromagnetic) into starches and sugars (chemical energy).
States of Energy
Most often, the conversion is between potential and kinetic energy.
All forms of energy can be in either of two states: Potential Kinetic
Kinetic-Potential Energy Conversion
Roller coasters work because of the energy that is built into the system. Initially, the cars are pulled mechanically up the tallest hill, giving them a great deal of potential energy. From that point, the conversion between potential and kinetic energy powers the cars throughout the entire ride.
Kinetic vs. Potential Energy
At the point of maximum potential energy, the car has minimum kinetic energy.
Kinetic-Potential Energy Conversions
As a basketball player throws the ball into the air, various energy conversions take place.
Ball slows down Ball speeds up
Conversions Involving Chemical Energy
Chemical energy comes from the food you eat.
Your body uses chemical energy to function.
Energy Conversions in Living Things
Photosynthesis uses the sun’s light energy to create chemical energy for the plant.
In this way, light energy is changed into chemical energy.
When you eat, that chemical energy is converted into kinetic energy for you to use.
Other energy conversions
In an electric motor, electromagnetic energy is converted to mechanical energy.
In a battery, chemical energy is converted into electromagnetic energy.
The mechanical energy of a waterfall is converted to electrical energy in a generator.
Energy Conversions
In an automobile engine, fuel is burned to convert chemical energy into heat energy. The heat energy is then changed into mechanical energy.
Chemical Heat Mechanical
Who cares?
Energy conversions are needed for everything we do.
Energy and Machines
Machines make work easier by changing the size or direction of force.
Some machines change the energy put into them into other kinds of energy.
Review for fun!
Roller coaster energy
Chapter 9Chapter 9
Energy: Forms and ChangesEnergy: Forms and Changes
Section 3: Conservation of
Energy
Essential Questions
How is energy conserved in a closed system?
What is the law of conservation of energy?
What are some examples of how thermal energy is always a result of energy conversion?
Why is perpetual motion impossible?
The Law of Conservation of Energy
Energy can be neither created nor destroyed by ordinary means. It can only be converted from one form
to another. If energy seems to disappear, then
scientists look for it – leading to many important discoveries.
Where Does the Energy Go?
Energy can not be lost. Roller coaster example: Some of
the potential and kinetic energy is released as thermal energy because of FRICTION
A Closed System
A closed system – a group of objects that transfer energy only to each other
If all types of energy are added up, you can see none is lost, just changed
Law of Conservation of Energy
Energy cannot be created or destroyed.
The total amount of energy in a closed system is always the same.
Any number of conversions could take place, though.
Thermal Energy
Any time an energy conversion takes place, some is converted to thermal energy. This is why there is no such thing as perpetual motion.
This thermal energy is due to FRICTION.
Energy Efficiency
Energy efficiency is a comparison before and after conversion
Energy conversions that waste less energy are efficient
Aerodynamic cars are an example
Chapter 9Chapter 9
Energy: Forms and ChangesEnergy: Forms and Changes
Section 4: Energy
Resources
Essential Questions
What are some energy resources? How is the sun the source of most
energy on Earth? What are the advantages and the
disadvantages of using various energy resources?
Energy resources
Energy resources are natural resources that can be converted into other forms of energy to do work.
Non-renewable resources cannot be replaced or can only be replaced very slowly.
Fossil Fuels
Fossil fuels – energy resources formed from buried plant and animal remains millions of years old.
Nonrenewable resources: petroleum (gasoline, plastics, etc); natural gas; coal
Electrical Energy from Fossil Fuels
Fossil fuels are the main source of electrical energy in the U.S.
Electrical generators convert a fossil fuels’ chemical energy into electrical energy
Fossil fuels are burned, thermal energy turns water to steam, steam converts to kinetic energy by powering a turbine, creating electricity
Nuclear Energy
Like fossil fuel power plants, nuclear power plants use thermal energy, using steam
Nuclear energy is generated from radioactive elements
Nuclear fission occurs when nuclei of atoms are split into smaller nuclei, releasing nuclear energy
Non-renewable resource
Renewable Resources
Renewable resources are replaced faster than they are used. Solar energy (solar cells) Hydroelectric energy (water-produced) Wind energy (wind turbines) Geothermal energy (thermal energy
caused by the heating of the Earth’s crust)
Biomass (organic matter burned to release energy)
Non-renewable vs. renewable
Both have advantages and disadvantages
Copy and study the table on page 262 of the classroom textbook.