Newton’s Gravity
Gravity between two masses is this kind of force: it pulls them together.
Attractive
Free fall is constant acceleration due to this.
Gravity
This model puts Earth at the center of the universe.
Geocentric
Kepler’s first law says each planet’s path is this shape.
An ellipse
Galileo’s law of falling bodies says these objects have uniform acceleration.
All
If either mass increases, the gravitational force does this.
Increases
In Newton’s cannon thought experiment, enough speed lets the shot do this around Earth.
Orbit (fall around Earth)
This model puts the Sun at the center and sends Earth around it.
Heliocentric
Kepler’s second law says a line from the sun to a planet sweeps equal amounts of this in equal times.
Area
This scientist measured the gravitational constant with hanging masses and a twist.
Henry Cavendish
If two masses are moved farther apart, the gravitational force does this.
Decreases
Objects in orbit are doing this the whole time, which is why astronauts float.
Free fall
Copernicus still used circular orbits, so he still needed these extra loops.
Epicycles
A planet moves faster when it is this relative to the Sun.
Closer
G tells you this about gravity.
Its strength
Gravity can act across empty space, so it is this type of force
A field force
A gravitational field vector at each point points toward this.
The massive body
Brahe kept Earth still and had the Sun go around Earth while the planets went around the Sun; that model is called this.
Geo-heliocentric
Kepler’s third law says a farther planet takes longer to do this.
Complete one orbit
Apparent weightlessness happens because this supporting force is missing.
The normal force
G stands for this in Newton’s law: a measure of gravity’s strength.
The gravitational constant
Double the distance between two masses and the gravitational pull between them becomes this.
One-fourth as large
Nearby objects appear to shift against a distant background when you change viewing place; that shift is called this.
Parallax
Newton obtained Kepler’s third-law pattern by setting gravity equal to this kind of force.
Centripetal force
Newton’s laws plus universal gravitation together explained Galileo’s falling bodies and these orbital rules.
Kepler’s laws