acceleration	The rate of change of velocity
amplitude	The height of a wave.
angular acceleration	The rate at which angular velocity is changing.
angular momentum	A vector quantity defined relative to a rotation axis and defined as the product of an object's moment of inertia and its angular velocity.
angular velocity	A vector quantity whose magnitude is its speed of rotation (radians/second) and whose direction is defined by the axis of rotation.
center of mass	A point relative to an object that acts as if all the mass of the object is concentrated there.
centripetal force	A force that causes motion in a circle.
clockwise	In the same rotation direction as the hands of a clock.
contact time	The time a satellite is in communication with a ground station.
Far Ultraviolet Spectroscopic Explorer (FUSE)	A space telescope designed to observe light in the far ultraviolet part of the electromagnetic spectrum.
force	A push or pull.
free fall	The condition of an object moving under the influence of no force other than the force of gravity.
frequency	The number of revolutions per unit time.
gravity	One of the fundamental forces of nature. It was described by Newton in terms of the masses of the objects experiencing the force and the distance of separation of the objects.It was described by Einstein as a distortion of space and time.
incident light	Light that falls on a surface.
moment of inertia	The property of an object associated with its resistance to rotation.It depends on the objects mass and the distribution of mass with respect to the axis of rotation.
monochromatic	Refers to light of only one wavelength.
newton	A unit of force.
normal	Direction perpendicular to a surface.
orbit	The path of a planet around the sun or a satellite around a planet.
period	The period of a satellite is the time it takes to complete one orbit.
polychromatic	Refers to light of more than one wavelength.
reaction wheel	A disk whose rate of spin can be used to turn a spacecraft.
reciprocal	The reciprocal of a number is 1 divided by the number.
satellite	An object that is bound to another object , such as a planet, by the gravitational force.
scientific notation	A usefull way to represent numbers that are very large or very small.Thiis representation Is a number equal to or greater than 1 but less than 10 times 10 to some power.For example 1,451 is 1.451 x 103.
SI units	A system of units used by the international scientific community.For example, in SI units, mass is expressed in kilograms and length is always given in meters.
significant figures	The number of meaningful digits in a number.
spectrometer	An instrument that spreads light into its component wavelengths.
torque	A vector quantity whose magnitude is the product of force and lever arm. Applying a torque to a stationaryobject will make it rotate in the same way applying force to an object will make it move in a straight line.
vector	A quantity defined by both magnitude and direction in space.
wavelength	The distance between corresponding parts of a wave.
weightlessness	The condition experienced by an object in free fall.The object appears to move without experiencing the force of gravity.