Flashcards in Lecture 2 Deck (46):
Is Andromeda our closest galaxy?
No, it is millions of ly away, outside the Milky Way
What kind of object is Andromeda Galaxy?
An Extragalactic object
How do we know Andromeda Galaxy will collide with us?
It has a radial velocity coming towards us, and no significant tangential velocity. All the stars we see are blue-shifted, which means they are coming towards us.
Will the collision between us and Andromeda include any other galaxies?
Yes, the Triangulum Spiral
What will happen to other stars once we collide with Andromeda?
They will not hit each other, but will change their orbits
What is the definition of speed?
Rate at which object moves (SCALAR)
What is the definition of velocity?
Rate at which object moves in a specific direction (VECTOR)
What is the definition of acceleration?
Any change in velocity over time
What did Galileo postulate about gravity?
All objects fall at the same rate (ignoring air resistance)
What is the definition of Inertia?
A measure of an object's resistance to change in motion
What is an inertial frame?
An environment which allows us to estimate motion by observation, e.g. not a moving car, but the Princeton Campus
What is Newton's first law of motion?
object in motion will remain in motion unless acted on my a net unbalanced force
What is Newton's first law of motion re: momentum?
An object will maintain a constant momentum unless acted upon by an outside force.
What is Newton's Second Law of Motion?
F=ma; The acceleration of a body is parallel and directly proportional to the force acting on that body
What is Newton's third law of motion?
For every action force, there is an equal opposite reaction force
What is the quantity used to represent inertial mass in rotational dynamics?
Moment of inertia
What is angular momentum?
rotational velocity x rotational inertia; the measure of how hard it is to stop the rotating body
What two factors effect angular momentum?
The distance from the axis and the mass of the rotating body
Why do objects move at a constant speed if no force acts on them?
Because momentum is conserved
How can the total momentum change?
By an external force acting on the objects
How do individual objects change momentum?
Through equal and opposite force (Collisions)
What is the parallel of force in rotational dynamics?
Why does the earth not fall into the sun?
Gravitational force is not a torque, so it does not affect the orbit; it only stops the acceleration from allowing Earth to exit the orbit
What is a Syzygy?
When three bodies align in a near-straight line
What is appulse?
The closest apparent approach of two bodies
What is conjunction?
When two bodies are in the same ecliptic plane
What is the Greatest Elongation?
WHen one object is furthest from the sun or another object
What is Opposition?
The greatest elongation when two bodies are opposite the sun
What is a quadrature?
When two bodies make a right angle
What is a transit?
When a smaller body passes in front of a larger body
What is occultation?
When a larger body passes in front of a smaller body
What is an eclipse?
When a body completely/partially disappears from view
Which planet has the most angular momentum?
What are the two different definitions of weight?
1. gravity pulling down (Pushing up) 2. person's gravity pulls up on the earth (pushing down)
How does free-fall occur?
When you have gravity pulling down (Weight 1) and no person's gravity pushing down (weight 2) you are in free-fall
What are the two conditions required for an eclipse?
1. a new moon (solar) or full moon (lunar) 2. the moon must be at one of the nodes of its orbit
What are the nodes of the moon's orbit?
points where the moon's slightly tilted orbit crosses the earth's ecliptic orbit; happens not quite every six months
What are the three main types of energy?
Kinetic, Radiative, Potential
What is radiative energy?
Energy that is emitted in the form of light / heat
What is the umbra?
The point in an eclipse where the sunlight is completely blocked
What is the penumbra?
The point in the eclipse where the sunlight is partially blocked
What is the totality?
WHen the sunlight is completely blocked during an eclipse
When does a total solar eclipse occur?
When the moon is especially close to the earth, and creates a large shadow
When does an annuler eclipse occur?
When the moon is especially close to the earth, and the umbra does not even reach the earth
When does a partial solar eclipse occur?
When only part of the sun is blocked