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Chapter 4: Gravitation and the Waltz of the Planets
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Gravity
Terms in this set (59)
acceleration
the rate at which an object's velocity changes due to a change in speed, a change in direction, or both
air drag
A force that opposes the motion of an object through air. A portion of the object's energy is transferred to the air molecules
aphelion
the point in its orbit where a planet is farthest from the Sun
conic selection
the curve of intersection between a circular cone and a plane; this curve can be a circle, ellipse, parabola, or hyperbola
conjunction
the geometric arrangement of a planet in the same part of the sky as the Sun, so that the planet is at an elongation of 0 degrees
conservation of energy
a law of physics stating that energy can change forms and be tranfered from one object to another but cannot be created or destroyed
deferent
a stationary circle in the Ptolemaic system along which another circle (an epicycle) moves, carrying a planet, the Sun, or the Moon
direct motion
the apparent eastward movement of a planet seen against the background stars
eccentricity
a number between 0 and 1 that describes the shape of an ellipse
ellipse
a conic section obtained by cutting completely through a circular cone with a plane
elongation
the angular distance between a planet and the Sun as viewed from Earth
epicycle
a moving circle in the Ptolemaic system about which a planet revolves
escape speed
the speed needed by an object (such as a spaceship) to leave a second object (such as a planet or star) permanently and to escape into interplanetary
focus (of an ellipse)
One of two points inside an ellipse such that the combined distance from the two foci to any point on the ellipse is a constant
force
a push or pull that acts on an object
geocentric model
an Earth-centered theory of the universe
gravitational force
the force with which all matter attracts all other matter
gravitational potential energy
Energy associated with Earth's pull on an object toward Earth's center. This energy increases with an object's distance from Earth.
gravity
the force with which all matter attracts all other matter
greatest eastern elongation
the configuration of an inferior planet at its greatest angular distance east of the Sun
greatest western elongation
the configuration of an inferior planet at its greatest angular distance west of the Sun
heliocentric model
a Sun-centered theory of the universe
hyperbola
a conic section formed by cutting a circular cone with a plane at an angle steeper than the sides of the cone
inferior conjunction
the configuration when an inferior planet is between the Sun and the Earth
inferior planet
a planet that is closer to the Sun than Earth is
Kepler's first law
the statement that each planet moves around the Sun in an elliptical orbit with the Sun at one focus of the ellipse
Kepler's second law
the statement that a planet sweeps out equal areas in equal times as it orbits the Sun; also called the law of equal areas
Kepler's third law
a relationship between the period of an orbiting object and the semimajor axis of its elliptical orbit
kinetic energy
the energy possessed by an object because of its motion
law of equal areas
the statement that a planet sweeps out equal areas in equal times as it orbits the Sun
law of universal gravitation
a formula deduced by Isaac Newton that expresses the strength of the force of gravity that two masses exert on each other
major axis (of an ellipse)
the longest diameter of an ellipse
mass
a measure of the total amount of material in an object
neap tide
an ocean tide that occurs when the Moon is near first-quarter or third-quarter phase
Newtonian mechanics
the branch of physics based on newton's laws of motion
Newton's first law of motion
the statement that a body remains at rest, or moves in a straight line at a constant speed, unless acted upon by a net outside force; the law of inertia
Newton's form of Kepler's third law of motion
a relationship between the period of two objects orbiting each other, the semimajor axis of their orbit, and the masses of the objects
Newton's second law of motion
a relationship between the acceleration of an object, the object's mass, and the net outside force acting on the mass
Newton's third law of motion
the statement that whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first body
Occam's razor
the notion that a straightforward explanation of a phenomena is more likely to be correct than a convoluted one
opposition
the configuration of a planet when it is at an elongation of 180 degrees and thus appears opposite the Sun in the sky
orbital energy
The net energy of an orbiting object due to its kinetic and gravitational potential energy. The farther a planet orbits from the Sun, the greater its orbital energy
parabola
a conic section formed by cutting a circular cone at an angle parallel to one of the sides of the cone
parallax
the apparent displacement of an object due to the motion of the observer
perihelion
the point in its orbit where a planet or comet is nearest the Sun
period (of a planet)
the interval of time between successive geometric arrangements of a planet and an astronomical object, such as the Sun
Ptolemaic system
the definitive version of the geometric cosmogony of ancient Greece
retrograde motion
the apparent westward motion of a planet with respect to background stars
semimajor axis
One-half of the major axis of an ellipse. For an orbiting object, the semimajor axis is also equal to the average orbital distance
sidereal period
the orbital period of one object about another as measured with the respect to the stars
speed
distance travelled divided by the time elapsed to cover that distance
spring tides
an ocean tide that occurs at new moon and full moon
superior conjunction
the configuration of a planet being behind the Sun as viewed from Earth
superior planet
a planet that is more distant from the Sun than is Earth
synodic period
the interval between successive occurrences of the same configuration of a planet
tidal force
a gravitational force whose strength and/or direction varies over a body and thus tends to deform the boidy
universal constant of gravitation
the constant of proportionality in Newton's law of gravitation
velocity
the speed and direction of an object's motion
weight
the force with which gravity acts on a body
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