nats 1311 - from the cosmos to earth law of conservation of energy energy can be neither created nor...

NATS 1311 - From the Cosmos to Earth

Law of Conservation of Energy

• Energy can be neither created nor destroyed.

• It merely changes it form or is exchanged between objects.

• This principle (or law) is fundamental to science.

• The total energy content of the Universe was determined in the Big Bang and remains the same today.


Conversion of Energy

Throwing a baseball

Nuclear energy (nuclear fusion on sun) - Radiative energy (sunlight) - Chemical energy (photosynthesis) - Chemical energy in pitcher’s body (from eating plants) - Mechanical kinetic energy (motion of arm) - Mechanical kinetic energy (movement of the baseball). Thus, ultimate source of KE in baseball is mass energy stored in hydrogen of Sun - created in Big Bang.

Hydroelectric dam

Gravitational - mechanical - electrical

Nuclear reactor

Nuclear - thermal - mechanical - electrical

CarChemical - thermal - mechanical


Temperature and Thermal Energy

Why does water burn your skin so much quicker than air?Why is falling into a 32º F lake more dangerous than standing outside naked on a 32º F?

Temperature - measure of the average kinetic energy of the particles in a substance - particles in box on right have higher temperature - higher velocity = more KE = higher temperature

Both boxes have same temperature - particles have same average velocity/KE - box on right has more thermal energy - energy contained in a substance - more particles


This diagram compares three common temperature scales. The Fahrenheit scale is used in the United States, but nearly all other countries use the Celsius scale. Scientists prefer the Kelvin scale because O K represents

absolute zero, the coldest possible temperature.


Conversion Between Celsius and Fahrenheit

ºF = ºC x 9/5 + 32º

ºC = (ºF - 32) x 5/9


STATES OF MATTER:

Gas — fixed quantity

Liquid— fixed quantity and size, shape conforms to container

Solid— fixed quantity, size and shape


The state of matter is determined by its temperature.

Consider water:

Below 32º F - ice - relatively low KE - each molecule tightly bound to it neighbors - solid

At 32º F molecules have enough energy to break solid bonds of ice - remain together but move relatively freely - liquid

At 212º F water boils and turns to gas - molecules break free of all bonds with neighbors - move independently of other molecules - gas


Size

Virus Smallest Living Thing 10 millionth of 1 cm

10-5 cm

Molecule 1/100 of a Virus 10-7 cm

Atom1 1/10 of a Molecule 10-8 cm

Nucleus 1/100,000 of an Atom 10-13 cm

Proton

Neutron

1/10 of a Nucleus 10-14 cm

Quark Much smaller than a Proton

???

1size of atom = 1 cm

1 cm 1000 km

1000 km = 600 miles, the distance from Dallas to El Paso

Structure of Matter


Atom

nucleus electrons

e-

protonsneutrons

p+n

Atom - comes from Greek word for “indivisible”. Named by Democritus (c. 470 - 380 B.C.) - believed that if a piece of matter, e.g., a rock, could be broken into pieces small enough that nothing smaller could be possible.


Charge

Electrical charge is a fundamental physical property that is always conserved - like energy.

The proton is positively charged - 1 positive basic unit of charge.

The electron is charged negatively - 1 negative basic unit of charge.

The neutron is neutral.

Like charges repel and unlike charges attract - electromagnetic force.

Electron bound to atom by electromagnetic bonding - positive charge of nucleus - negative charge of electrons. In natural state - equal number of electrons and protons - atom has neutral charge.

Nucleus bound by strong nuclear force - stronger than repellent electromagnetic force of protons that tries to break nucleus apart.

NATS 1311 - From the Cosmos to EarthThe “size” of an Atom• Although it is the smallest part of the atom, most of the atom’s mass

is contained in the nucleus.• The electrons do not “orbit” the nucleus; they are “smeared out” in a

cloud which give the atom its size.

Solids made up of almost completely empty space - solidity comes from electric interactions between charged particles in its atoms and the strange quantum laws governing electron behavior.

One drop of water contains 1022 - 1023 atoms - more than stars in the universe


Hydrogen

e-

p+

1 electron1 proton0 neutrons


Helium

e-

p+

n

e-

np+

2 electrons 2 protons2 neutrons


Hydrogen

e-

p+

n

Deuterium

isotope

1 electron1 proton1 neutron

An isotope of an element has the same number of protons but a different number of neutrons.


The particles in the nucleus determine

the element and isotope.

===

===

==

+++

+


Periodic Table of the Elements

118 known elements as of 2008 - 91 occur naturally. Only 111 officially recognized and named. The first man-made element was Technetium in 1937. All man-made elements radioactive with short half-lives so that any that were present at the formation of Earth have long since decayed.


The periodic table groups elements with similar chemical properties together - largely driven by electron structure of elements. Electrons exist on shells - each shell has a maximum allowable number of electrons. Many chemical properties dependent on number of electrons in outer shell.


p+

n

e-

np+

atomic number = 2

atomic mass number = 4

What if an Electron is Missing?

The atom becomes an ion with a positive charge.

He+1


Plasma- 4th State of Matter

Temperature so high that atoms are ionized - negatively charged free electrons move among positively charged ions - motions controlled by electromagnetic forces (repulsion/attraction) instead of collisions.


What if two or more atoms combine to form a particle?

p+ p+

8p+

8n

molecule

H2O (water)


Electron Orbits

• Electrons can gain or lose energy while they orbit the nucleus - this energy is the electric potential energy - as opposed to the other two energies an atom has - mass energy and kinetic energy.

• When electrons have the lowest energy possible, we say the atom is in the ground state.

• When electrons have more energy than this, we say the atom is in an excited state.

• When electrons gain enough energy to escape the nucleus, the atom is ionized.


Electron Energy Levels• Electrons can not have just any energy while orbiting the nucleus.• Only certain energy values are allowed.• Electrons may only gain or lose certain specific amounts of energy.

• Each element (atom and ion) has its own distinctive set or pattern of energy levels - holds the key to studying of distant objects in the universe.

• This diagram depicts the energy levels of Hydrogen.

• 1 eV (electron volt) = 1.6 X 10-19 J

Electron jumps to higher energy levels can only occur with addition of the particular amounts of energy representing differences between possible energy levels. Energy levels are quantized - study of electron energy levels called quantum mechanics. Atom gains this energy either from KE of another atom colliding with it or from absorption of energy carried by light - falls to lower energy level by emitting light or transfer of energy by collision.


Nuclear Fission

Neutron strikes nucleus - breaks it apart into two separate atoms - different elements - releases another two neutrons + energy - if enough material is present (critical mass) - run away reaction leads to explosion - atomic bomb. Controlled reaction - nuclear reactor. In reactor, fuel doesn’t produce as many neutrons - neutron absorber is also used to absorb some of the neutrons - so reaction doesn’t run away. A nuclear reactor cannot explode!


Nuclear Fusion

In nuclear fusion - two atoms collide and combine to form single atom/element - tremendous amount of energy released. Velocity or KE of atoms and/or pressure must be large enough to overcome repulsive electromagnetic force of outer cloud of electrons - such as in center of Sun. Mass of resultant atom slightly less (~ 3%) than two original atoms together - mass converted to energy. Note that the fusion reaction in a hydrogen bomb is started by an atomic bomb.


Light


Four Ways in Which Light can Interact with Matter

1. emission – matter releases energy as light

2. absorption – matter takes energy from light

3. transmission – matter allows light to pass through it

4. reflection – matter repels light in another direction


Mirror reflects light at angle equal to incoming angle -

Most materials reflect light randomly - scattering. Movie screen scatters light into array of beams that reaches every member of the audience


Materials that transmit light are transparent

Materials that absorb light are opaque

In general - some combination of reflection, absorption, and transmissionRed glass transmits red light - absorbs all other colorsGreen grass reflects green light - absorbs all other colors

NATS 1311 - From the Cosmos to EarthLight

What is light? - A vibration in an electromagnetic field through which energy is transported.

Light as a wave

Light as a particle E = hf photon

f = c

The dual nature of light or wave-particle duality:

nats 1311 - from the cosmos to earth law of conservation of energy energy can be neither created nor...

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