Lecture 3 Flashcards
How did Galileo solidify the Copernican revolution?
Galileo overcame major objections to the Copernican view
Three key objections rooted in Aristotelian view were:
- Earth could not be moving because objects in air would be left behind
- Non circular orbits are not “perfect” as heavens should be
- If Earth were really orbiting Sun, we’d detect stellar parallax
Overcoming the First objection (nature of motion)
Galileo’s experiments showed that objects in air would stay with Earth as it moves.
Aristotle thought that all objects naturally come to rest.
Galileo showed that objects will stay in motion unless a force acts to slow them down (nowadays this is called Newton’s first law of motion, but Galileo knew this already)>
Galileo likely also realized that gravity would keep objects bound to Earths Surface
Overcoming the second objection
Brahe’s observations of a comet and a supernova already challenged this idea.
Using his telescope
Galileo Saw:
Sun spots on the sun (imperfections)
Mountains and valleys on the moon (proving it is not a perfect sphere).
He did this in 1609
Overcoming the third objection (Parallax)
Tycho thought he had measured stellar distances, so lack of the parallax seemed to rule out an orbiting Earth
Galileo showed stars must be much farther than. Tycho thought - in part by using his telescope to see the Milky Way contains individual stars.
If stars were much farther away, then lack of detectable parallax was no longer so troubling
What did Galileo saw in 1610
Four moons orbiting Jupiter, proving that not all objects orbit Earth.
Europa, Ganymede, lo, Callisto
Newton 1687: Explanation of Kepler’s Laws
Realized that the same physical laws that operate on Earth also operate in the heavens
One universe
Discovered laws of motion and gravity
Force = mass x acceleration
What determines the strength of gravity?
The universal law of gravitation:
Every mass attracts every other mass.
Attraction is directly proportional to the product of their masses.
Attraction is inversely proportional to the square of the distance between the centers
Consequences of Newton’s law of gravity
Kepler’s first two laws apply to all orbiting objects, not just planets.
Elipses are not the only orbital paths. Orbits can be:
Bound
Unbound
Parabola
hyperbola
Energy
Is the ability to do something (usually denoted as “work”)
Its a form of currency of Nature: Whenever you want to do something, you have to spend energy: Lifting a grocery bag costs energy. thinking costs energy, every heartbeat costs energy
You replenish your body’s energy reservoirs through the consumption of food
Units of energy
Joule (J), electron volt (eV), 1J = 6.2e18 eV
Power
Energy used or produced per time
Unit: Watt = Joule per second: 1W=1J/s
Basal metallic rates in humans
How do we experience light?
The warmth of sunlight tells us that light is a form of energy.
We can measure the flow of energy (i.e. energy delivered per time) in light in units of Watts: 1 Watt = 1W = 1J/S
How do light and matter interact
Emission
Absorption
Transmission
Transparent objects transmit light
Opaque objects block (absorb) light
Reflection/scattering
What is light
Light can act either like a wave or like a particle
Particles of light are called photons
