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Newton's realization about gravity.

-gravity extends beyond the Earth and is universal
-the moon is falling around Earth
-all objects are attracted to all other objects in the universe in a way that involves only mass and distance.


constant that tells how much the circumference of a circle will grow when diameter is increased

C = D*pi


gravitational constant

G tells how much Force of gravity (F) will increase when you increase the masses of the objects involved.


Gravity decreases...

as the objects get farther apart


what is responsible for our tides?

combined effect of the sun and the moon on Earth.
-Water is very "moveable" and responds to the gravitational fields more easily than continents or oceanic crusts do.
-Thus the water bulges out, and the Earth spins beneath the bulge.


Why does the moon not hit Earth, according to Newton?

The moon is falling towards Earth, but it has great enough tangential velocity to avoid hitting Earth.


What would happen if tangential velocity of a planet was reduced to zero?

Their motion would be straight towards the sun and would crash into it.


Newton's Law of Universal Gravitation

Every object attracts every other object with a force.


Law of Universal Gravitation Equation

Force ~ (mass(1) * mass(2))/distance^2
F ~ (m(1)m(2))/d^2


Equation of Universal Gravitation

F = G * (m(1)m(2)/d^2)


G =

6.67 * 10^-11 N*m^2/kg^2


Law of Universal Gravitation Equation for G

G = F/(m(1)m(2)/d^2) = 6.67 * 10^-11 N*m^2/kg^2


Inverse-square law

When a quantity varies as the inverse square of its distance from its source.


Gravity decreases according to...

the inverse-square law. The force of gravity weakens as the square of distance.


Gravitational field

The force field that exists in the space around every massive body.


Earth can be thought of as being surrounded...

by a gravitational field that interacts with objects and causes them to experience gravitational forces.


What is the gravitational field of Earth at its center?

Zero. Things weigh nothing.


What is force against earth?

The sensation that is interpreted as weight.



Absence of a support force.


Ocean tides are caused by...

differences in the gravitational pull of the moon on opposite sides of Earth.


Spring Tide

High or low tide that occurs when the sun, Earth, and moon are all lined up


Neap tide

Occurs when the moon is halfway between a new moon and a full moon, in either direction.


When a massive star collapses into a black hole, there is no...

change in the gravitational field at any point beyond the original radius of the star.



The deviation of an orbiting object from its path around a center of force caused by the action of an additional center of force.


Why are there no large objects in the solar system today with very low tangential velocities?

They crashed into the sun long ago.


When a satellite companion to a star that collapses to become a black hole, how will the orbit of the companion satellite be affected by the star's transformation into a black hole?

The orbit will not be affected. The star's mass has not changed and the distance from center of mass to center of mass has not changed, so the gravitational field remains the same.


Why are planets and moons round?

Gravity caused them to attract themselves together before they became solid. Any "corners" were pulled in so that planets and moons are giant spheres.


geostationary/geosynchronous orbits

-exact same spot at all times
-used to give very precise information about a specific location


A geometric fact about the curvature of the Earth is that its surface drops a vertical distance of __?__ meters for every ___?___ meters tangent to its surface.

5 meters; 8000 meters


What would happen if your satellite was launched with a tangential speed of 9 km/s or 10 km/s?

-would get farther away from the Earth before being pulled back down, resulting in an elliptical orbit.