rate at which an object is moving
ex: 100 kilometers/hr (60 miles/hr) is speed. Telling us the car will cover a distance of 100 km if driven at this speed for an hour


speed in a certain direction
ex: 100 km/hr going due north


change in velocity (change in either speed of direction)
*increasing or decreasing
If you don't feel yourself being pushed by acceleration, it means ur moving at constant velocity (airplane)

acceleration of gravity

Galileo on leaning tower of Pisa: gravity accelerates all objects by the same amount, regardless of their mass
*objects only fall slower due to air resistance
*on earth accl of gravity=9.8m/s^2


Mass x Velocity
~the only way to change an object's momentum is to apply a force to it


can change an object's momentum, causing it to accelerate

Mass vs weight

mass=amount of matter in your body, an object's mass is the same no matter where it's located. Your weight varies with the strength of gravity or other forces acting on the object

Elevator scale mass vs weight

When elevator is stationary or moving at constant velocity, the scale reads your normal weight.
~when elevator accelerates upward, the floor exerts a greater force than it does when you are at rest. You feel heavier>greater weight
~elevator accelerates do

Weightless object

Object becomes weightless when it's in free fall even though its mass is unchanged
~astronauts are weightless in space bc they are in a CONSTANT STATE OF FREE FALL

Newton's 3 laws of motion

1. object moves at constant velocity if there is not net force acting upon it. OBJECTS AT REST REMAIN AT REST, OBJECTS IN MOTION REMAIN IN MOTION IF NO FORCE
2. force =mass x acceleration (f=ma) amount of acceleration depends on object's mass & net force

Conservation laws in Astronomy

What keeps a planet rotating and orbiting the sun?
-conservation of angular momentum

Conservation of angular momentum

Planet's rotation and orbit cannot change unless it transfers angular momentum to another object. their orbits & rotation rates remain steady ,
~mass x velocity x radius (distance from sun) = constant. As one variable changes, the others change so that th

Where do objects get their energy?

Energy is always conserved-it can be neither created nor destroyed. Objects received energy from: kinetic, radiative, and potential


Catholic church still believed earth was the center of the universe.
1. Discovered 4 moons orbiting Jupiter not earth. He also observed that venus goes through phases in a way that it must orbit the sun and not earth. Supported Copernican view, earth move

Kinetic energy

Energy of motion
-thermal energy (heat energy)

Potential energy

Energy that is stored and held in readiness. (gradational, mass, energy E=mc^2, chemical=electron bonds in food, muscles, wood

Radiative energy

light energy

Thermal energy

heat energy. Sum of KE's of all particles in system being considered. VS temperature :gives measure of average velocity or KE of particles

Why do all objects fall at the same speed?

due to acceleration of gravity (gravity accelerates all objects by the same amount)
& newton's 2nd law: feather is light so accelerates faster, hammer is heavy needs more force to accelerate

Newton's law of interia

1. (momentum p=mv) obj remains at rest or moving at a straight line unless acted upon by external force

Newton's 2nd law

F=ma a force applied to a body with mass will cause it to accelerate (change speed & direction)
-acceleration=change in velocity
-speed=distance/time (no direction)

Newton's 3rd law

Every action/force has an equal and opposite reaction/force
~as mass gets bigger, acceleration gets smaller (heavier things, more air resistance & harder to push)

What keeps a planet rotating and orbiting the sun?

law of conservation of angular momentum
-total angular momentum can never change
-angular momentum=mvr, r=orbital radius (distance from the sun)
1. earth will keep orbiting as long as nothing comes to take angular momentum away
2. ang momentum depends on

Newton's law of gravitation

1. every mass attracts every other mass through force called GRAVITY
2. strength of gravitational force attracting 2 objects is directly proportional to the product of their masses
3. inverse square law. ex: doubling distance between 2 objects weakens for

Newton's version of kepler's laws

He found ellipses aren't the only possible orbital paths. ~Bound orbits: orbits in which an object goes around other object over and over
~unbound orbits: path that brings an object close to another object just once ex: comets that enter inner solar syste

Newton's version of kepler's third law

A generalization of Kepler's third law used to calculate the masses of orbiting objects from measuring the orbital period and distance; usually written as p^2 = (4pie^2) / G(M1 + M2)^a3,
!found out if you change the mass of one, it doesn't really have any

Conservation of energy

Energy cannot be created or destroyed; it may be changed from one form into another, but the total amount of energy never changes


total energy/total velocity of all particles
ex: coffee has a higher temp than your body but lower heat bc it has less mass

Critical velocities for orbits

zero velocity=straight line
circular velocity=fire ball at 8 km/s around earth for perfect circle (anything under 8 is bound orbit)

escape velocity

11.3 km/s, kinetic beats potential. parabola. kinetic=potential unbound orbit
over 11.3 km/s =hyperbola

orbit bound

if PE > KE

Unbound orbit

if KE>PE (hyperbola, or parabola PE=KE)

How does gravity cause tides

tidal force: stretches the earth from center in 2 directions even though the moon is tugging harder in only one side, causes earth to bulge towards and away from moon. Earth's rotation carries us through 2 bulges each day, giving us 2 daily high and low t

free fall

The motion of a falling object when the only force acting on it is gravity.