The Tarantula Nebula is more than 1,000 light-years in diameter -- a giant star forming region within our neighboring galaxy the Large Magellanic Cloud (LMC). Within the Tarantula, intense radiation, stellar winds and supernova shocks from the central young cluster of massive stars, energize the nebular glow and shape the spidery filaments. Around the Tarantula are other violent star-forming regions with young star clusters, filaments and bubble-shaped clouds.

Homework #2 will be posted shortly

It will be due Wednesday, September 23, noon

A hallmark of science is that

theories are testable

With Galileo’s observations, the revolution begun by Copernicus was nearly complete… The structure of the universe had been totally changed.

The motions of the planets were understood, at least from a geometrical perspective. Earth was no longer a “special” place in the universe.

The crowning achievement was yet to come - discovering the laws of nature and that naturally led to the newly determined structure.

Sir Isaac Newton (1642-1727)

Invented calculus

Invented the reflecting telescope

Connected gravity and planetary forces

Universal Law of Gravitation Between every two objects there is an attractive force,

the magnitude of which is directly proportional to the mass of each object and inversely proportional to the square of the distance between the centers of the objects.

● Extending Kepler’s Law #1, Newton found that ellipses were not the only orbital paths.

● All orbits are “conic sections”– ellipse (bound)– parabola (unbound)– hyperbola (unbound)

● Orbital motion takes place around the center of mass

Orbital Paths from Law of Gravitation

The Center of Mass

In Kepler's Laws, the Sun is fixed at a point in space (a focus of an ellipse) and the planet revolves around it. Why is the Sun privileged?

Kepler had mystical ideas about the Sun, endowing it with almost god-like qualities that justified its special place.

Newton demonstrated that the the Sun does not occupy a privileged postion and in the process he modified Kepler's 3rd Law.

The center of mass is familiar to anyone who has ever played on a see-saw. The fulcrum point at which the see-saw will exactly balance two people sitting on either end is the center of mass for the two persons.

m1d1 = m2d2

Newton realized that in the planet-Sun system the planet does not orbit around a stationary Sun (a planet exerts as much gravitational force on the Sun as the Sun does on a planet).

Instead, Newton proposed that both the planet and the Sun orbited around the common center of mass for the planet-Sun system.

This led Newton to modify Kepler's 3rd Law.

Recall Kepler’s 3rd law: P2 / a3 = constant

Fg = Gm1m2/d2

P2 = 42 a3 / G (m1 + m2)

G is known as the universal gravitational constant.

Newton’s Version of Kepler’s Third Law

If you can measure the orbital period of two objects (P) and the distance between them (a), then you can calculate the sum of the masses of both objects (m1 + m2).

A Universe of Matter and Energy

What is matter?

What is energy?

Matter – material such as rocks, water, air; “stuff” composed of atoms

Energy – makes or has the potential to make matter move!

The history of the universe, including biological organisms, is based upon the interplay between

matter and energy.

Three Basic Types of Energy

• kinetic– energy of motion

• potential– stored energy; e.g., chemical,

gravitational, electrical, etc.• radiative

– energy transported by light (electromagetic radiation)

Conservation of Energy

Fundamental law of nature

Energy can be neither created nor destroyed

It can change form or be exchanged between objects.

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

K.E.

P.E. R.E.

Kinetic Energy (K.E.): energy of motion

K.E. = 1/2 mv2

(m is mass, v is velocity)

On the microscopic level:

temperature

is a measure of the

average kinetic energy

of particles within a substance

Temperature Scales

Temperature vs. Heat● Temperature is the average

kinetic energy.● Heat (thermal energy) is the

total kinetic energy.

lower T higher T

same T

less heat more heat

Sound waves are a form of kinetic energy on a microscopic level

(organized vibration of molecules)

Applying what we’ve learned -

pizza vs. soup

caution in the kitchen

The very first ever Blonde GUY joke..... And well worth the wait!

An Irishman, a Mexican and a Blonde Guy were doing construction work on scaffolding on the 20th floor of a building.

They were eating lunch and the Irishman said, "Corned beef and cabbage! If I get corned beef and cabbage one more time for lunch, I'm going to jump off this building."

The Mexican opened his lunch box and exclaimed, "Burritos again! If I get Burritos one more time I'm going to jump off, too."

The blond opened his lunch and said, " Bologna again! If I get a bologna sandwich one more time, I'm jumping too."

The next day, the Irishman opened his lunch box, saw corned beef and cabbage, and jumped to his death.

The Mexican opened his lunch, saw a Burrito, and jumped, too.

The blonde guy opened his lunch, saw the bologna and jumped to his death as well.

At the funerals, the Irishman's wife was weeping. She said, "If I'd known how really tired he was of corned beef and cabbage, I never would have given it to him again!"

The Mexican's wife also wept and said, "I could have given him tacos or enchiladas ! I didn't realize he hated Burritos so much."

Everyone turned and stared at the blonde's wife. The blonde's wife said …

"Don't look at me. He makes his own lunch"

Potential Energy:

Energy that is “stored” within an object and that has the potential of being released in a different form

Gravitational Potential Energy

● gravitational potential energy is the energy which an object stores due to its ability to fall

● It depends on:– the object’s mass (m)– the strength of gravity (g)– the distance which it can fall (d)

m

d

g

● P.E. = mgd

● gravitational potential energyg● P.E. = mgd

Mass-Energy Potential Energy

● mass-energy: energy is stored in matter itself

● this mass-energy is what would be released if an amount of mass, m, were converted into energy

E = mcE = mc22

[ c = 3 x 108 m/s is the speed of light]

Chemical Potential Energy● Chemical potential energy:

energy stored chemical bounds

There are many additional examples of potential energy. e.g.,

stretched springs, …

Energy, while conserved, can be

transformed from one type of energy to

another

Potential Kinetic

Potential Kinetic

Kinetic Potential

Orbits & Energy

MaximumKinetic Energy

MaximumPotentialEnergy

Downhill

Uphill

From the

perspective of

energy, which

planet is more

difficult to reach

from the Earth?

Mars

Venus

From the

perspective of

energy, which

planet is more

difficult to reach

from the Earth?

Mars

It is “uphill”

ConceptTest

The gravitational potential energy of an interstellar cloud of gas that is slowly shrinking in size …

(yellow) stays the same

(red) slowing changes into other forms of energy

(green) slowly increases

(blue) interstellar clouds do not have gravitational potential energy

ConceptTest

The gravitational potential energy of an interstellar cloud of gas that is slowly shrinking in size …

(yellow) stays the same

(red) slowing changes into other forms of energy

(green) slowly increases

(blue) interstellar clouds do not have gravitational potential energy

ConceptTestIn the not too distant future scientists will develop an engine that produces more energy than it uses. This statement is …

(yellow) likely to be true

(red) false

(green) difficult to determine if this will happen or not.

(blue) this has already happened, but the government is suppressing this discovery.

ConceptTestIn the not too distant future scientists will develop an engine that produces more energy than it uses. This statement is …

(yellow) likely to be true

(red) false

(green) difficult to determine if this will happen or not.

(blue) this has already happened, but the government is suppressing this discovery.