Exam 2 (Ch 3-6) Flashcards by Courtney W

2 motions Aristotle divided motion into

Terrestrial

Celestial

How well did you know this?

Not at all

Perfectly

Motion that happened on earth

Terrestrial

How well did you know this?

Not at all

Perfectly

Motion that happened in the skies

Celestial

How well did you know this?

Not at all

Perfectly

2 categories of terrestrial motion

Natural

Violent

How well did you know this?

Not at all

Perfectly

Type of motion that a rock has when it is released from a height and falls to the ground or of the motion smoke has when ascending up towards the sky
Except for the celestial motion, all of this is vertical motion (either up or down)
Based on the “four elements” out of which everything on Earth is constituted: earth, water, air, fire
Did not require any outside influence

Natural motion

How well did you know this?

Not at all

Perfectly

Neglecting air resistance, two objects that are
dropped together will fall together, regardless of
their weights, shapes or of the materials of which
they are made; an object falls because of gravity

Galileo’s Law of Falling

How well did you know this?

Not at all

Perfectly

Celestial objects have another “essence”, ether
Only natural motion of objects made out of the ether.
Perfect and circular: the sun and the planets around the earth

Celestial motion

How well did you know this?

Not at all

Perfectly

Require a push or a pull: for example, moving a cart requires something or someone to push or to pull the cart
Always horizontal
If a motion is not “natural motion” it will eventually stop, unless a push or a pull (i.e., a force) acts on it

Violent motion

How well did you know this?

Not at all

Perfectly

If no external influences act on a moving object, then it will move in a straight line (at a constant velocity forever)
A body that is subject to no external forces must maintain an unchanging velocity
If an object is at rest its velocity is 0

The Law of Inertia

How well did you know this?

Not at all

Perfectly

Distance traveled in each unit of time

Speed

How well did you know this?

Not at all

Perfectly

The total distance traveled in an interval divided by the time of that interval

Average speed

How well did you know this?

Not at all

Perfectly

The speed of an object at a specific instant in time (as opposed to the speed measured over a relatively large time interval, which is the average speed)

Instantaneous speed

How well did you know this?

Not at all

Perfectly

You drive 100 miles in 2 hours. What is your average speed?

Average speed = distance traveled / time
s = d/t
= (100 mi)/(2 hr)
= 50 MPH

How well did you know this?

Not at all

Perfectly

A quantity that is specified by only a number

Example: a time interval 12 hours, a distance of 240 miles

Scalar

How well did you know this?

Not at all

Perfectly

A quantity that that needs a number and a direction to be specified
Example: a velocity of 30 miles/hr due south a distance of 240 miles due north

Vector

How well did you know this?

Not at all

Perfectly

The difference between speed and velocity

Scalars vs. vectors

How well did you know this?

Not at all

Perfectly

Change of velocity with time
(change in velocity)/(time interval to make change)
A change in velocity can be a change in the speed of an object, in the direction the object is traveling in, or a change in both the speed and direction of the object

Acceleration

The acceleration of any freely falling object; on earth this is about 10 m/s^2

Acceleration due to gravity

g = 9.8 m/s^2

What does the law of inertia mean for an object at rest?

An object at rest will remain at rest if it is not subject to a net external force

What does the law of inertia mean if an object is moving with a constant speed in a straight line?

An object moving in a straight line at constant speed will continue moving in a straight line at constant speed if it is not subject to a net external force

For all cases of constant acceleration if the object is falling what is the acceleration?

The acceleration due to gravity, g = 9.8 m/s^2

The acceleration is proportional to the net force, but inversely proportional to the mass
a = Fnet/m
Fnet = ma

Newton’s 2nd Law

Fnet if the forces are in opposite directions

F1 - F2

Fnet if the forces are in the same direction

F1 + F2

A measure of the amount of inertia of the object (how difficult it is to get the object going if it is at rest) Same here or on the moon

Mass

The force exerted by the gravitational pull of Earth on the object, mg Different here than on the surface of the Moon; the value of g on the moon is different, it is about 1.6 m/s^2, g on Earth is 10 m/s^2

Weight

Whenever one body exerts a force on a second body, the second body exerts a force on the first one. The force exerted by the second body on the first is equal in magnitude and opposite in direction than the force exerted by the first body on the second (the law of force pairs) Ex: the bat exerts a force on the ball, and the ball exerts a force on the bat that is equal in magnitude and opposite in direction

Newton’s Third Law

If there are no external forces acting on the components of a system, the total momentum of a system remains unchanged) regardless of the forces the parts of the system exert on each other

Conservation of momentum

Stars larger than about 10 masses of the sun go through multiple cycles of core collapse and heating, fusing in turn helium, carbon and all the way up to iron But once they get to iron, the star is in trouble – iron will not fuse, the cycle stops and gravity takes over once again The star implodes and then explodes About 10% to 20% of the star remains after this; the remnant collapses quickly

Supernova

For cases in which the original mass of the star is between 10 and 30 times the mass of our Sun the gravitational force is strong enough that not only are atoms not able to exist, nuclei can no longer exist either: electrons collapse into protons and form neutrons The entire star becomes a solidly packed ball of neutrons

Neutron star

If the original star is more massive than about 30 times the sun’s mass, even a neutron star cannot survive – the star collapses all the way to a single point (a singularity) Nothing, not even light, can escape its gravitational pull if it gets too close

Black hole

Done whenever an object a force (F) acting on an object | moves the object a distance (d) in the direction of the force (F); fd

Work

The capacity to do work Ex: by lifting the block, we gave it the capacity (or potential) to do work When you do work on something, you give it this in some form

Energy

The product of weight times the height above the ground Ex: in doing work on our block by lifting it, we gave the block this

Gravitational potential energy/gravitational energy

Work is a transfer of energy. Work reduces the energy of the system doing the work and increases the energy of the system on which work is done by an amount equal to the work done

The work-energy theorem

The energy of motion related to its velocity and its mass ½mv^2

Kinetic energy (EKIN, KE)

The total energy of all the participants in any process remains unchanged throughout that process. That is, energy cannot be created or destroyed. Energy can be transformed (changed from one form to another), and it can be transferred (moved from one place to another), but the total amount always stays the same There are no known exceptions Experiments have found that energy is always conserved, although it may change its form

Law of conservation of energy

5 other types of energy

``` Electrical Chemical Nuclear Radiant (light) Mass energy (E = mc^2 – Einstein) ```

Equal work done divided the time it takes to do it (work /time), Watt (W)

Power (p)

In what kind of path would the planets move if no force acted on them?

Straight line with no acceleration

The moon's acceleration is directed what direction?

Inward, toward the center of Earth

A white dwarf star is about the size of what?

The earth