15.1 energy and its forms today’s special hw check - vocab 15 test results standards video on...

15.1 Energy and Its Forms

Today’s special

• HW check - Vocab 15• Test results• Standards• Video on Energy• Notes 15 Energy• HW I due next time!• Movie• Lab next time…


Energy

PAf.1: Explain how the law of conservation of energy applies to the transformation of various forms of energy (including mechanical energy,

electrical energy, chemical energy, light energy, sound energy, and thermal energy).

PAf.2: Explain the factors that determine potential and kinetic energy and the transformation of one to the other.

PAf.3: Explain work in terms of the relationship among the force applied to an object, the displacement of the object, and the energy

transferred to the object.PAf.4: Use the formula W = Fd to solve problems related to work

done on an object.PAa.1: Generate hypotheses on the basis of credible, accurate, and

relevant sources of scientific information. PAa.2: Use appropriate laboratory apparatuses, technology, and

techniques safely and accurately when conducting a scientific investigation. PAa.9: Use appropriate safety procedures when conducting

investigations.


We must always change, renew,

rejuvenate ourselves; otherwise we harden.

Johan Wolfgang von Goethe

Fact: The average lifespan of a major league baseball: 7 pitches.


In an avalanche, a mass of loose snow, soil, or rock suddenly gives way and slides down the side of a mountain.

The avalanche releases a great amount of energy.


How are energy and work related?

Energy is the ability to do work.

Energy and Work

Work is a transfer of energy.


Work and energy are closely related. • Energy is known by the changes it causes. • Work is done when a force moves an object

through a distance. Energy is transferred by a force moving an object through a distance.

• Both work and energy are typically measured in joules (J).

Energy and Work


Energy has different forms. A. The sun gives off energy in the form of heat and

light.

Energy and Work



light.

B. Plants convert sunlight into food.

Energy and Work



light.

B. Plants convert sunlight into food.

C. People convert food energy into muscle movement.

Energy and Work


What factors does the kinetic energy of an object depend on?

The energy of motion is called kinetic energy.

Kinetic Energy

The kinetic energy of any moving object depends upon its mass and speed.


• Doubling the mass in the formula doubles the kinetic energy.

• Doubling the speed quadruples the kinetic energy.

Kinetic Energy


Calculating Kinetic Energy

A 0.10-kilogram bird is flying at a constant speed of 8.0 m/s. What is the bird’s kinetic energy?

Kinetic Energy


Read and UnderstandWhat information are you given?

What unknown are you trying to calculate?

Kinetic Energy


Plan and Solve

What equation contains the given quantities and the unknown?

Substitute the known values in the formula for KE.

Kinetic Energy


Look Back and CheckIs your answer reasonable?

Kinetic Energy



It seems reasonable, because the bird has a low mass, so it would not have much kinetic energy.

Kinetic Energy


1. A 70.0-kilogram man is walking at a speed of 2.0 m/s. What is his kinetic energy?

Answer:

Kinetic Energy


1. A 70.0-kilogram man is walking at a speed of 2.0 m/s. What is his kinetic energy?

Answer:

KE = (0.50)(70.0 kg)(2.0 m/s)2 = 140 J

Kinetic Energy


2. A 1400-kilogram car is moving at a speed of 25 m/s. How much kinetic energy does the car have?

Answer:

Kinetic Energy


2. A 1400-kilogram car is moving at a speed of 25 m/s. How much kinetic energy does the car have?

Answer:

= (0.50)(1400 kg)(25 m/s)2

= 440,000 J

Kinetic Energy


3. A 50.0-kilogram cheetah has a kinetic energy of 18,000 J. How fast is the cheetah running? (Hint: Rearrange the equation to solve for v.)

Answer:

Kinetic Energy


How is gravitational potential energy determined?

Potential energy is energy that is stored as a result of position or shape.

Potential Energy

An object’s gravitational potential energy depends on its mass, its height, and the acceleration due to gravity.


When this musician pulls the string of her cello to one side, the string is stretched and gains potential energy.

Potential Energy


Gravitational Potential Energy

Potential energy that depends upon an object’s height is called gravitational potential energy.

This type of potential energy increases when an object is raised to a higher level.

Potential Energy


This diver has gravitational potential energy as she stands at the end of a diving board.

She gained the potential energy by doing work—by climbing up the steps to the diving board.

Potential Energy


• The unit for mass is kilograms.• The unit for height is meters.• Acceleration due to gravity, g, has a value in

SI units of 9.8 m/s2 on Earth.• The unit for gravitational potential energy is

joules.

Potential Energy


Height is measured from the ground or floor or some other reference level.

Doubling either the mass of the object or its height doubles its gravitational potential energy.

Potential Energy


What is the potential energy relative to the water surface of a diver at the top of a 10.0-meter-high diving platform. Suppose she has a mass of 50.0 kilograms.

PE = mgh

= (50.0 kg)(9.8 m/s2)(10.0 m)

= 4900 kg•m2/s2 = 4900 J

Potential Energy


Elastic Potential Energy

The potential energy of an object that is stretched or compressed is known as elastic potential energy.

Something that is elastic springs back to its original shape after it is stretched or compressed.

Potential Energy


A compressed bicycle shock absorber and a wound-up toy robot both have elastic potential energy.

Potential Energy


What are the major forms of energy?

Forms of Energy

The major forms of energy are mechanical energy, thermal energy, chemical energy, electrical energy, electromagnetic energy, and nuclear energy.


All energy can be considered to be one of three forms:

• kinetic energy,• potential energy, and• energy in fields such as those produced by

electromagnetic waves.

Each of these forms of energy can be converted into other forms of energy.

Forms of Energy


Mechanical Energy

The energy associated with the motion and position of everyday objects is mechanical energy.

Mechanical energy is the sum of an object’s potential energy and kinetic energy.

Forms of Energy


Thermal Energy

The total potential and kinetic energy of all the microscopic particles in an object make up its thermal energy.

When an object’s atoms move faster, its thermal energy increases, and the object becomes warmer.

Forms of Energy


This molten metal is extremely hot. It contains a great deal of thermal energy.

Forms of Energy


Chemical Energy

Chemical energy is the energy stored in chemical bonds.

When bonds are broken, the released energy can do work. All chemical compounds, including fuels such as coal and gasoline, store energy.

Forms of Energy


This family is using the chemical energy of burning wood to produce thermal energy for heating marshmallows.

Forms of Energy


Electrical Energy

Electrical energy is the energy associated with electric charges.

Electric charges can exert forces that do work.

Forms of Energy


Electromagnetic Energy

Electromagnetic energy is a form of energy that travels through space in the form of waves.

Visible light and X-rays are examples of electromagnetic energy.

Forms of Energy


A. Lightning bolts transfer electric charge.

B. Galaxies are giant structures in space that typically contain billions of stars. The stars give off enormous amounts of electromagnetic energy.

Forms of Energy


Nuclear Energy

The nucleus of an atom is held together by strong and weak nuclear forces, which can store an enormous amount of potential energy.

• The energy stored in atomic nuclei is known as nuclear energy.

• Nuclear fission releases energy by splitting nuclei apart.

• Nuclear fusion releases energy when less massive nuclei combine to form a more massive nucleus.

Forms of Energy


Assessment Questions

1. How are work and energy related? a. Energy is the rate of doing work.

b. Work is a form of energy.

c. Work is the transfer of energy.

d. Energy is created by work.



1. How are work and energy related? a. Energy is the rate of doing work.

b. Work is a form of energy.

c. Work is the transfer of energy.

d. Energy is created by work.

ANS: C



2. A moving object with a mass of 10 kg has 320 J of kinetic energy due to its motion. How fast is the object moving?a. 64 m/sb. 32 m/sc. 8 m/sd. 10 m/s



2. A moving object with a mass of 10 kg has 320 J of kinetic energy due to its motion. How fast is the object moving?a. 64 m/sb. 32 m/sc. 8 m/sd. 10 m/s

ANS: C



3. Which of these is an example of elastic potential energy?a. a bow prepared to release an arrow

b. a rubber ball thrown into the air

c. a book about to fall from a table

d. a truck pulling a trailer



3. Which of these is an example of elastic potential energy?a. a bow prepared to release an arrow

b. a rubber ball thrown into the air

c. a book about to fall from a table

d. a truck pulling a trailer

ANS: A



4. A small airplane and a helicopter have identical masses. If the airplane’s altitude compared to the ground is three times that of the helicopter, how much more gravitational potential energy does the airplane have than the helicopter?

a. 0.333 times as much

b. 3 times as much

c. 6 times as much

d. 9 times as much



4. A small airplane and a helicopter have identical masses. If the airplane’s altitude compared to the ground is three times that of the helicopter, how much more gravitational potential energy does the airplane have than the helicopter?

a. 0.333 times as much

b. 3 times as much

c. 6 times as much

d. 9 times as much

ANS: B



5. The energy stored in the bonds between atoms of a compound is called a. electromagnetic energy.

b. chemical energy.

c. atomic energy.

d. thermal energy.



5. The energy stored in the bonds between atoms of a compound is called a. electromagnetic energy.

b. chemical energy.

c. atomic energy.

d. thermal energy.

ANS: B


Today’s special

• ISS tour 3

• HW I check; Q & A

• Energy Lab: due next!

• E.S.B.


Today’s special

• ISS tour 4

• Momentum Lab & Energy lab due (turn in now on front desk)

• Some notes

• HW II due next

• Energy graphic organizer

• Rubber band cars planning (design & supplies)

15.2 Energy Conversion and Conservation

As a meteor traveled through the atmosphere in October 1992, some of its kinetic energy was converted into light and heat. Upon impact, much of the meteor's remaining kinetic energy went into smashing the rear of this car in Peekskill, New York.


Energy Conversion

Can energy be converted from one form into another?

Energy can be converted from one form to another.


The process of changing energy from one form to another is energy conversion. The striking of a match is a good example.

• Muscles use chemical energy to move the match.

• Friction between the match and the matchbox converts kinetic energy into thermal energy.

• Chemical energy is converted into thermal energy and electromagnetic energy in the flame.

Energy Conversion


Energy is converted from one form to another as this match is lit.

Energy Conversion


Conservation of Energy

What is the law of conservation of energy?

The law of conservation of energy states that energy cannot be created or destroyed.


When energy changes from one form to another, the total energy remains unchanged, even though many energy conversions may occur.

In a closed system, the amount of energy present at the beginning of a process is the same as the amount of energy at the end.



The work done by friction changes kinetic energy into thermal energy.

• Friction within machinery reduces efficiency. Friction is a major cause of energy consumption in cars and factories.

• In many cases, most of a falling object’s potential energy is converted into thermal energy because of air resistance.



Although speed skaters slide quickly over smooth ice, they are still slowed down by friction with the air and the surface of the ice.



Energy Conversions

What energy conversion takes place as an object falls toward Earth?

The gravitational potential energy of an object is converted to the kinetic energy of motion as the object falls.


One of the most common energy conversions is between potential energy and kinetic energy.

• An avalanche brings tons of snow from the top of a mountain to the valley floor.

• The elastic potential energy of a compressed spring is converted into kinetic energy as the spring expands.

• Energy conversions can go from kinetic to potential energy or from potential to kinetic energy.

Energy Conversions


Some gulls use energy conversion to obtain food by dropping oysters onto rocks. Kinetic energy causes the shell to break on collision with the rock.

Energy Conversions


Energy Conversion in Pendulums

A pendulum consists of a weight swinging back and forth from a rope or string.

• At the highest point in its swing, the pendulum has zero kinetic energy and maximum potential energy.

• As the pendulum swings downward, potential energy is converted to kinetic energy.

• At the bottom of the swing, the pendulum has maximum kinetic energy and zero potential energy.

Energy Conversions


Pendulum clocks use pendulums to maintain accurate time.

The time it takes for a pendulum to swing back and forth once is precisely related to its length.

Energy Conversions


Energy Conversion and the Pole Vault

In the pole vault, an athlete uses a flexible pole to propel himself over a high bar.

Energy Conversions


Some of the pole-vaulter’s kinetic energy is converted into elastic potential energy as the pole bends. The pole springs back into shape, propelling the pole-vaulter upward.

• As the pole-vaulter rises, his kinetic energy decreases while he gains gravitational potential energy.

• Once the highest point has been reached, his gravitational potential energy begins to convert back to kinetic energy.

Energy Conversions


Energy Conversion Calculations

When friction is small enough to be ignored, and no mechanical energy is added to a system, then the system’s mechanical energy does not change.

Mechanical energy = KE + PE

Energy Conversions


The law of conservation of energy applies to any mechanical process. If friction can be neglected, the total mechanical energy remains constant.

Energy Conversions


Conservation of Mechanical Energy

At a construction site, a 1.50-kg brick is dropped from rest and hits the ground at a speed of 26.0 m/s. Assuming air resistance can be ignored, calculate the gravitational potential energy of the brick before it was dropped.

Energy Conversions


Read and UnderstandWhat information are you given?

What unknown are you trying to calculate?

Energy Conversions


Plan and Solve

What equations or formulas contain the given quantities and the unknown?

Energy Conversions


Plan and Solve

What equations or formulas contain the given quantities and the unknown?

Because the brick falls without air resistance, the conservation of mechanical energy equation can be used.

Energy Conversions


Plan and SolveYou will also need to use the formula for kinetic energy (KE).

Note that the KE at the beginning is zero because the brick has not yet begun to fall. Also, when the brick hits the ground, its potential energy is zero. Substitute these values into the conservation of energy formula.

Energy Conversions


Plan and Solve

Substitute the formula for KE.

Substitute the known values and calculate the PE.

Energy Conversions



Energy Conversions



Check the answer by finding the initial height of the brick, using PE = 507 J = mgh. Substituting in m and g gives h = 34.5 m. This is a reasonable height for an object in free fall to reach a speed of 26.0 m/s.

Energy Conversions


1. A 10-kg rock is dropped and hits the ground below at a speed of 60 m/s. Calculate the gravitational potential energy of the rock before it was dropped. You can ignore the effects of friction. Answer:

Energy Conversions


1. A 10-kg rock is dropped and hits the ground below at a speed of 60 m/s. Calculate the gravitational potential energy of the rock before it was dropped. You can ignore the effects of friction. Answer: (PE)beginning = (KE)end = ½mv2

=(0.50)(10 kg)(60 m/s)2 = 18,000 J

Energy Conversions


Energy Conversions

2. A diver with a mass of 70.0 kg stands motionless at the top of a 3.0-m-high diving platform. Calculate his potential energy relative to the water surface while standing on the platform, and his speed when he enters the pool. (Hint: Assume the diver’s initial vertical speed after diving is zero.)

Answer:


2. A diver with a mass of 70.0 kg stands motionless at the top of a 3.0-m-high diving platform. Calculate his potential energy relative to the water surface while standing on the platform, and his speed when he enters the pool. (Hint: Assume the diver’s initial vertical speed after diving is zero.)

Answer:

Energy Conversions


3. A pendulum with a 1.0-kg weight is set in motion from a position 0.04 m above the lowest point on the path of the weight. What is the kinetic energy of the pendulum at the lowest point? (Hint: Assume there is no friction.)

Answer:

Energy Conversions


3. A pendulum with a 1.0-kg weight is set in motion from a position 0.04 m above the lowest point on the path of the weight. What is the kinetic energy of the pendulum at the lowest point? (Hint: Assume there is no friction.)

Answer:

(PE)beginning = mgh

= (1.0 kg)(9.8 m/s2)(0.04 m) = 0.4 J;

at the beginning, KE = 0, and at the lowest point, PE = 0;

therefore (PE)beginning = (KE)end = 0.4 J

Energy Conversions


Energy and Mass

How are energy and mass related?

Einstein’s equation, E = mc2, says that energy and mass are equivalent and can be converted into each other.


Albert Einstein developed his special theory of relativity in 1905. This theory included the now-famous equation E = mc2.

• E is energy, m is mass, and c is the speed of light.

• The speed of light is an extremely large number, 3.0 × 108 meters per second.

• A tiny amount of matter can produce an enormous amount of energy.

Energy and Mass


Albert Einstein made important contributions to many areas of physics.

His theory of special relativity showed that energy and mass are equivalent.

Energy and Mass


Suppose 1 gram of matter were entirely converted into energy.

E = mc2 = (10–3 kg) × (3 × 108 m/s) × (3 × 108 m/s)

= 9 × 1013 kg•m2/s2

= 9 × 1013 J

1 gram of TNT produces only 2931 joules of energy.

Energy and Mass


In nuclear fission and fusion reactions, however, large amounts of energy are released by the destruction of very small amounts of matter.

The law of conservation of energy has been modified to say that mass and energy together are always conserved.

Energy and Mass



1. What energy conversion occurs as a result of friction? a. chemical energy to thermal energy

b. kinetic energy to potential energy

c. kinetic energy to thermal energy

d. potential energy to thermal energy



1. What energy conversion occurs as a result of friction? a. chemical energy to thermal energy

b. kinetic energy to potential energy

c. kinetic energy to thermal energy

d. potential energy to thermal energy

ANS: C



2. At what point in a pendulum’s swing does it have maximum kinetic energy?a. the highest point of the swingb. the lowest point of the swingc. halfway between the lowest and highest pointd. same at all positions of the swing



2. At what point in a pendulum’s swing does it have maximum kinetic energy?a. the highest point of the swingb. the lowest point of the swingc. halfway between the lowest and highest pointd. same at all positions of the swing

ANS: C



3. Based on Einstein’s equation for the equivalence of energy and mass, how much energy is produced by the conversion of 1 kilogram of mass to energy? a. 3x103 J

b. 3x105 J

c. 9x105 J

d. 9x1013 J



3. Based on Einstein’s equation for the equivalence of energy and mass, how much energy is produced by the conversion of 1 kilogram of mass to energy? a. 3x103 J

b. 3x105 J

c. 9x105 J

d. 9x1013 J

ANS: D



1. According to the law of conservation of mass, energy can be converted from one from to another but not created or destroyed.

TrueFalse



1. According to the law of conservation of mass, energy can be converted from one from to another but not created or destroyed.

TrueFalse

ANS: F, law of conservation of energy

15.3 Energy Resources

Crude oil is pumped out of the ground, refined, and turned into gasoline, fuel oil, and other oil products.


What are the major nonrenewable sources of energy?

Nonrenewable energy resources exist in limited quantities and, once used, cannot be replaced except over the course of millions of years.

Nonrenewable Energy Resources

Nonrenewable energy resources include oil, natural gas, coal, and uranium.


Oil, natural gas, and coal are known as fossil fuels.

• They were formed underground from the remains of once-living organisms.

• Fossil fuels account for the great majority of the world’s energy use.

• These fuels are not distributed evenly throughout the world.

Nonrenewable Energy Resources


What are the major renewable sources of energy?

Renewable energy resources are resources that can be replaced in a relatively short period of time.

Renewable Energy Resources

Renewable energy resources include hydroelectric, solar, geothermal, wind, biomass, and, possibly in the future, nuclear fusion.


Most renewable energy resources originate either directly or indirectly from the sun.

• The sun and Earth are constantly releasing large amounts of energy.

• This energy could be used for generating electric power, heating buildings, or other purposes.



Hydroelectric Energy

Energy obtained from flowing water is known as hydroelectric energy.

• As water flows downhill, its gravitational potential energy is converted into kinetic energy.

• This kinetic energy turns turbines connected to electric generators.



Most modern hydroelectric plants rely on dams built across rivers. The major advantages of hydroelectric energy include its low cost to produce and lack of pollution.

Dams, however, cause a variety of environmental problems.



Hoover Dam was built across the Colorado River on the Arizona-Nevada border.

This 221-meter-tall structure can generate over 2 million kilowatts of power.



Solar Energy• Sunlight converted into usable energy is called

solar energy. • In passive solar designs, sunlight heats a

building without using machinery.• In active solar energy systems, sunlight heats

flat collection plates through which water flows.



• Sunlight can also be converted directly into electrical energy by means of solar cells, also known as photovoltaic cells.

• A few large solar electric plants use mirrors that concentrate sunlight to produce electricity.

• The benefits of solar energy depend on the climate.



Geothermal Energy• Geothermal energy is thermal energy beneath

Earth’s surface. • In some regions, especially near volcanoes,

geothermal energy is used to generate electricity.

• Geothermal energy is nonpolluting but is not widely available.



A. A solar electric plant uses solar cells to convert sunlight into electricity.

B. A geothermal plant in California uses Earth’s thermal energy to generate electricity.



Other Renewable Resources

The chemical energy stored in living things is called biomass energy. Biomass can be converted directly into thermal energy or converted into a high-energy alcohol fuel.

A hydrogen fuel cell generates electricity by reacting hydrogen with oxygen. Hydrogen fuel cells can be used to convert energy from renewable resources.



A form of hydrogen is also the most likely raw material for another future source of energy, nuclear fusion.

The process of fusion will probably produce little pollution or radioactive waste. Scientists have been working on sustained fusion for years, but many challenges remain.



Which energy resources are most commonly used around the world? How is energy use changing over time? The table shows total world energy use in 1991 and 2000. Energy use is measured in British thermal units, or Btu (1 Btu = 1055 J). Note that petroleum includes oil and related fuels.

World Energy Use


1. Using Tables What was the world’s largest source of energy in 1991? In 2000?

Answer:

World Energy Use


1. Using Tables What was the world’s largest source of energy in 1991? In 2000?

Answer: Petroleum in both years.

World Energy Use


2. Analyzing Data In general, how did usage change from 1991 to 2000?

Answer:

World Energy Use


2. Analyzing Data In general, how did usage change from 1991 to 2000?

Answer: Each type of energy use increased between 1991 and 2000.

World Energy Use


3. Graphing Make a circle graph of world energy use by source for the year 2000.

World Energy Use


3. Graphing Make a circle graph of world energy use by source for the year 2000.

Answer:

World Energy Use

Other 1%

Nuclear fission 6%

Hydroelectric power 7%

Natural gas 23%

Coal 24%

Petroleum 39% Petroleum

Coal Natural gas Hydroelectric power Nuclear fissionOther


4. Analyzing Data What percentage of world energy use in 2000 was accounted for by fossil fuels?

Answer:

World Energy Use


4. Analyzing Data What percentage of world energy use in 2000 was accounted for by fossil fuels?

Answer: Approximately 86%.

World Energy Use


5. Predicting How might total world energy use be different in 2020? Explain.

Answer:

World Energy Use


5. Predicting How might total world energy use be different in 2020? Explain.

Answer: Based on the trend between 1991 and 2000, the total world energy use will likely be significantly higher in 2020 than it was in 2000. The percentage of energy resources in the “other” category will increase by 2020.

World Energy Use


How can energy resources be conserved?

Conserving Energy Resources

Energy resources can be conserved by reducing energy needs and by increasing the efficiency of energy use.


Finding ways to use less energy or to use energy more efficiently is known as energy conservation.

• Making appliances, cars, and even light bulbs more energy efficient is a way of reducing energy use.

• Energy-efficient purchases often cost more initially, but can save money in fuel costs over time.



Mass transportation systems include buses, trains, and streetcars.

Using mass transit can reduce energy use.




1. Which of the following is a nonrenewable energy resource? a. geothermal energy

b. hydroelectric energy

c. hydrogen fuel cells

d. natural gas



1. Which of the following is a nonrenewable energy resource? a. geothermal energy

b. hydroelectric energy

c. hydrogen fuel cells

d. natural gas

ANS: D



2. What is one of the advantages of hydroelectric power?a. can be used everywhereb. does not cause any environmental problemsc. uses energy produced by Earthd. inexpensive compared to other energy sources



2. What is one of the advantages of hydroelectric power?a. can be used everywhereb. does not cause any environmental problemsc. uses energy produced by Earthd. inexpensive compared to other energy sources

ANS: D



3. Which of these actions is not a way to conserve energy resources? a. turn off lights when they are not needed

b. increase usage of mass transit

c. reduce the cost of energy production

d. increase efficiency of appliances



3. Which of these actions is not a way to conserve energy resources? a. turn off lights when they are not needed

b. increase usage of mass transit

c. reduce the cost of energy production

d. increase efficiency of appliances

ANS: C


Today’s special

• HW II check

• Practice test

• Rubber band car work time/supply check

• Test & car race next time!


Today’s special

• Turn in Practice test on front desk

• Test 6 Work and Energy

• Enter answers in Smartresponse, turn in paper test with sentences & essay/math problem

• Work silently reading & doing vocabulary (without talking) until ALL have finished testing

• Race day!

• Vocab 7 due next class!

15.1 energy and its forms today’s special hw check - vocab 15 test results standards video on...

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