Gravity and Light
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20 Terms
It would take over _______, edge to
edge, to reach to the nearest star
3 billion Earths; nearest
Light from the nearest galaxy like ours takes
_______ to reach us
over 2 million years
The oldest stars have ages over _______
times the typical human lifespan
150 million times
The universal law of gravitation
tells us the strengthof the gravitational force between two objects based on their masses and the distance between them.
Every mass attracts
every other mass
If the distance between two masses is doubled, the
gravitational force between the masses
decreases by a factor of 4
Kepler's laws apply to
all orbiting objects, not just
planets.
Ellipses are
not the only orbital paths
Orbits can be
bound (ellipses and circles) or unbound (parabola or hyperbola)
Because of angular
momentum conservation, orbiting objects
orbit around their center of mass.
Center of Mass
m1*d1 = m2*d2
p =
orbital period
a =
average orbital distance (between centers)
(M1 + M2) =
sum of object masses
Newton's laws of gravity and motion showed that the
relationship between the _______ (p) and _______ (a) of a system tells us _______ of the system.
orbital period; average orbital distance; the total mass
In space, an object or gas cloud has _______ when it is _______.
more gravitational energy; spread out than when it contracts
A contracting cloud converts _______ to _______.
gravitational potential energy; thermal energy
Kepler's First Law
each planet's orbit about the Sun is an ellipse. The Sun's center is always located at one focus of the orbital ellipse
Kepler's Second Law
the imaginary line joining a planet and the Sun sweeps equal areas of space during equal time intervals as the planet orbits; planets do not move with constant speed along their orbits
Kepler's Third Law
the squares of the orbital periods of the planets are directly proportional to the cubes of the semi-major axes of their orbits; implies that the period for a planet to orbit the Sun increases rapidly with the radius of its orbit