# Intro to Astronomy - Chapter 5

## 23 terms · Gravity

### Newton

created 3 laws of motion; studied motion and physics

### Newton's first law

law of inertia; an object continues at rest or in uniform motion in a straight line unless acted upon by some force

### Mass

measure of the amount of matter in an object (stays constant)

### Increases

as mass increases, inertia ______

### Weight

force of gravity on an object; it varies with your location

### Newton's second law

the acceleration of a body is directly proportional to the net force on it and inversely proportional to its mass

### Increases

as force increases, acceleration _____

### Decreases

as mass increases, acceleration _____

### Newton

the most common force unit

### Newton's third law

to every action, there is an equal and opposite reaction (law of action-reaction)

### Newton's law of universal gravitation

every particle in the universe attracts every other particle

### Directly

the gravitational force of attraction between objects is _____ proportional to the product of their masses

### Inversely

the gravitational force of attraction between objects is _____ proportional to the square of the distances between them

### in free-fall

astronauts appear weightless because they are _____

### Barycenter

the center of mass/gravity is known as the _____

### Orbital velocity

the velocity required to remain in circular orbit

### Closed orbit

elliptical or circular orbit

### Geosynchronus orbit

the object rotates with the rotation of Earth and remains above a fixed spot

### Open (escape) orbit

leads away from the central body never to return

### Angular momentum

measure of rotation of a body about some point

### Einstein

he studied the mass/energy relationship

### Curvature

the _____ of space-time (gravity) tells mass how to accelerate, and the mass tells space-time how to curve

### Most massive object

objects orbit each other and revolve around the center of mass, which is located closer towards the _______