15.1 Energy and Its Forms Cornell notes 10-4 and 15-1 10-4 What is fission? How does fission occur?...

15.1 Energy and Its Forms

Cornell notes 10-4 and 15-110-4•What is fission?•How does fission occur?•What is it used for?•What is fusion?•How does it occur?•Where can it be found

15-1•How is work and energy related?•Explain the following energies and any forms of these energies

– Kinetic– Potential– Mechanical– Thermal– Chemical– Electrical– Electromagnetic– nuclear


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.


I. Energy and its formsA. Energy and Work

1. Work and energy are closely related. 2. Energy- is the ability to do work.

a. Energy is known by the changes it causes. 3. Work- a transfer of energy.

a. Work is done when a force moves an object through a distance. Energy is transferred by a force moving an object through a distance.

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


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


B. Kinetic Energy- The energy of motion1. The kinetic energy of any moving object depends upon its

mass and speed. a. Doubling the mass in the formula doubles the kinetic

energy.b. Doubling the speed quadruples the kinetic energy.c. Formula:


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

?

.10

(8)2

KE=m=v2=

2

2

1mvKE

)/64)(10)(.5(. 22 smkgKE

JsmkgKE 2.3/2.3 22


2) 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.)

2

2

1mvKE

2

1

2

2

1

1

2mvKE

m

mv

m

KE 22

22v

m

KE

2)50(1

2

2

1000,18

1

2vkgJ

2)50(2

1000,18 vkgJ

kg

vkg

kg

J

50

)50(

50

)000,18(2 2

vsm

v

/27

720 2


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

Potential Energy


The musician adds energy to the cello string by plucking it.

• The energy stored in the stretched string is potential energy.

• The stored energy is converted into kinetic energy when the string is released and it vibrates.

Potential Energy


C. Potential Energy- is energy that is stored as a result of position or shape1. Gravitational Potential Energy- Potential energy that

depends upon an object’s height, mass, and the acceleration due to gravity.

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


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


1) The unit for mass is kilograms.

2) The unit for height is meters.

3) Acceleration due to gravity, g, has a value in SI units of 9.8 m/s2 on Earth.

4) The unit for gravitational potential energy is joules.

b. Formula:


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

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


e. 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


2. Elastic Potential Energy- The potential energy of an object that is stretched or compressed

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


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

Potential Energy


D. Forms of Energy1. All energy can be considered to be one of three forms:

a. kinetic energy,b. potential energy, andc. energy in fields such as those produced by

electromagnetic waves. d. Each of these forms of energy can be converted into

other forms of energy.


2. Mechanical Energy- The energy associated with the motion and position of everyday objects

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

3. Thermal Energy- The total potential and kinetic energy of all the microscopic particles in an object.

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


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

Forms of Energy


4. Chemical Energy- the energy stored in chemical bonds.

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


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

Forms of Energy


5. Electrical energy -the energy associated with electric charges.

a. Electric charges can exert forces that do work.

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

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


7. Nuclear Energy- The energy stored in atomic nuclei

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

b. Nuclear fission releases energy by splitting nuclei apart.

1) In nuclear fission, tremendous amounts of energy can be produced from very small amounts of mass.


The fission of uranium-235 yields smaller nuclei, neutrons, and energy.

Fission

Neutron



Fission

Neutron



Fission

Neutron

Energy


The fission of one nucleus can trigger a chain reaction.

Fission


Nuclear Energy from Fission

Nuclear power plants generate about 20 percent of the electricity in the United States.

In a nuclear power plant, controlled fission of uranium-235 occurs in a vessel called a fission reactor.

Nuclear power plants do not emit air pollutants.

Fission


Nuclear power plants do have safety and environmental issues.

• Workers in nuclear power plants need to wear protective clothing to reduce their exposure to nuclear radiation.

• Nuclear power produces radioactive isotopes with half-lives of hundreds or thousands of years.

Fission


Unfortunately, a product of controlled chain reactions is radioactive waste. A crane lowers drums of radioactive waste into a landfill in Hanford, Washington.

Fission


The Tokamak Fusion Test Reactor at the Princeton Plasma Physics Laboratory was one of the very few fusion reactors that have been built.

Fusion


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

1) As in fission, during fusion a small fraction of the reactant mass is converted into energy.

2) The sun and other stars are powered by the fusion of hydrogen into helium.


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

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15.1 Energy and Its Forms Cornell notes 10-4 and 15-1 10-4 What is fission? How does fission occur?...

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