• Support an argument that the gravitational force exerted by Earth on objects is directed down. (5-PS2-1)

• For any pair of interacting objects, the force exerted by the first object on the second object is equal in strength to the force that the second object exerts on the first, but in the opposite direction (Newton's third law). (6-8)

• The gravitational force of Earth acting on an object near Earth's surface pulls that object toward the planet's center. (5)

• 6-8: 4F/M3a. An unbalanced force acting on an object changes its speed or direction of motion, or both.

• 3-5: 4G/E1. The earth's gravity pulls any object on or near the earth toward it without touching it.

Cool classroom demo for illustrating inertia at rest.  A dollar bill is placed between two soda bottles; the top bottle is filled with water.  Upward/downward forces are balanced because the dollar acts as a sealant.  Quickly removing the dollar bill creates a net unbalanced force on the water, which whooshes into the soda bottle below.  Try teaming this teacher-led demo with the Pencil Drop below, which students could perform.

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