"Gravity!" Fundamentals Quiz

The word "gravity" is, by itself, utterly ambiguous.  Nonetheless, our students will refer to a wide swatch of constants, principles, and equations by this single word.  While that's not necessarily a problem in the context of a conversation with friends, the lack of specificity can get students confused and blown up when trying to solve test problems.

To the right is part of a recent fundamentals quiz about "gravity."  (You can click on it to read it at full size.) I listed every possible equation or constant that has any tenuous connection to "gravity," and I asked students to identify these items in words.  Here's a summary of correct and (real) incorrect answers:

(a) Correct: Net force on an object in uniform circular motion, or just centripetal force.  

      Incorrect: centrifugal force, net force, centripetal acceleration, gravitational force

(b) Correct: Gravitational force exerted by any massive object on another, or just gravitational force.

      Incorrect: Newton's law, gravitational field, g

(c) Correct:  acceleration of an object in uniform circular motion, or just centripetal acceleration

      Incorrect: centrifugal acceleration, acceleration, centripetal force, net force, gravitational acceleration

(d) Correct: Weight, force of a planet on an object on the planet's surface.

      Incorrect:  free-fall acceleration, mass

(e) Correct:  Gravitational field produced by a planet, free-fall acceleration

      Incorrect:  Force of gravity, force of g, Newton's law, force of a planet, centripetal force

(f) Correct:  Gravitational field, or free-fall acceleration

      Incorrect:  Force of gravity, gravity, weight, free-fall force, gravitational constant

(g) Correct:  Universal gravitation constant

      Incorrect: Newton's law, force of gravity, free-fall acceleration, gravitational field, gravity