Vis Visa: The Great Debate

Gottfried Leibniz argued that vis visa (or “living force” — which was supposed to be some kind of weird fluid transferred between objects) was equal to mv2 and was conserved when objects collided.

Isaac Newton thought that vis visa was a mystical crock, and that only mv was conserved. That way, it required God to keep the Universe from collapsing.

Leibniz and Newton hated each other already since they both claimed to have invented calculus. And because Newton believed in atoms and Newton didn’t. And because Leibniz hated Newton’s concept of invisible gravity. And who knows what else.

Vis Visa: The Great Debate

Johann Bernoulli of Switzerland proved that Leibniz was right. But the French thought that was mumbo jumbo from an effete elitist (a sissy snob).

The famous French author Voltaire even made fun of Bernoulli in his book Candide. (Voltaire was a champion of Newton, though.)

But, Voltaire’s mistress, Emilie Du Chatelet thought Bernoulli was right, especially after reading the experiments of Willem ‘s Gravesande.

Vis Visa: The Great Debate

‘s Gravesande’s experiment showed that the volume of the indentations made by brass balls dropped onto clay was proportional to the vis visa — mv2.

Newton was wrong.

‘s Gravesande’s experiment set the stage for modern theories of energy and energy conservation. The vis visa is now known as “kinetic energy” and is given by the expression:

KE = (1/2) mv2

Vis Visa: The Experiment

• You will repeat Gravesande’s experiment by dropping a steel ball from 7 heights onto a block of clay, using plastic tubes as guides.

• You will only drop once, but will have 3 observers measure the diameter of the indentation (they’re not that easy to see) using a ruler. MEASURE DIAMETERS in MM!

• After each drop, the clay block will be flipped and flattened.

• You will average the measurements, and use a formula to convert the diameters into volumes.

• You will then plot the indentation volume versus the drop height. If the vis visa (kinetic energy) is really (1/2) mv2 then the plot should be a straight line. If Newton was right, and the vis visa is mv, then the plot should curve downward.

Vis Visa: The Experiment

• Sketch the table and graph axes into your notebook:

40 squares high25 squares wide

Vis Visa: The Experiment

LEIBNIZ

NEWTON

Vis Visa: Volume of Indent

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V =π R3 cos3 θ dθθ

π2∫

V =π R3

32 −sinθ cos2 θ +2 ⎛

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⎠ ⎟ ⎡

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θ

Radius = R

Indent Diameter = D

θ = asin(D/2)

D