1. Lesson 13: Gravitational Force
Objective: define and explain gravity and its relationship to planets, stars, and galaxies

2. Gravity
A natural phenomenon by which all things with mass are brought toward one another, including planets, stars and galaxies.
*Mass is defined as the amount of matter in an
object.
-More mass = more gravitational force

3. Newton’s Law of Universal Gravitation
Describes gravity as a force which causes any two bodies to be attracted to each other, with the force proportional to the product of their masses and inversely proportional to the square of the distance between them.
F = force, m1 and m2 are the masses of the objects interacting, r is the distance between the centers of the masses and G is the gravitational constant

4. General Theory of Relativity
Proposed by Einstein in 1915
Describes gravity not as a force, but as a consequence of the curvature of spacetime caused by uneven distribution of mass/energy.
Most extreme example of this curvature of spacetime is a black hole.

7. Why are astronauts weightless in space?
For the same reasons that riders of a free-falling amusement park ride or a free-falling elevator are weightless. They are weightless because there is no external contact force pushing or pulling upon their body.
They aren’t floating, they are actually falling. They have the same acceleration as the space station or spaceship, they feel weightless.

8. Microgravity
A condition in which people or objects appear to be weightless
Micro - very small
There is gravity in space but it is very small. Gets weaker with distance.
Space is a vacuum which causes all objects to fall at the same rate regardless of their mass.