What does inertia measure, and what physical quantity is its measure?

The resistance to a change in motion, measured by mass

A swimmer pushes water backward. What force moves her forward?

The water's push on her (the reaction force)

It is less, because the Moon's gravity is weaker

Backward, opposite to the motion

Yes, because the net force is zero

Both are proportional to the inverse square of the distance

12questions. Pick an answer and you'll see why right away.

According to Newton's first law, an object moving at constant velocity has what net force acting on it?
What does inertia measure, and what physical quantity is its measure?
A net force of $24$ N acts on a $6.0$ kg object. What is its acceleration?
A crate is pushed forward with $50$ N against a friction force of $20$ N. What is the net force?
Why do the two forces of an action-reaction pair not cancel each other?
A swimmer pushes water backward. What force moves her forward?
An object has a mass of $8.0$ kg. Taking $g = 10$ m/s squared, what is its weight?
How does the weight of an object on the Moon compare with its weight on Earth?
In which direction does friction act on a box sliding forward across a floor?
A skydiver falls at constant terminal velocity. Is the skydiver in equilibrium?
What happens to the gravitational force between two masses if the distance between them is doubled?
What do Newton's law of gravitation and Coulomb's law have in common?