Quiz Question

One of a continuing series


This Quiz Question requires understanding of some very basic physics. You have to figure out what this basic understanding is in order to come up with the answer.

Look at the diagram. Here we have the proverbial frictionless machine/assembly. It moves left and right without resistance. On the right side of the platform is an electric battery. On the left side is a flywheel driven by a motor. The motor is connected to the battery by an electric cable. Electric power from the battery will drive the motor.

The flywheel starts off perfectly still—not rotating. Then the electric circuit is completed, and the motor starts to drive the flywheel. Soon the flywheel is rotating at some considerable rate, said not rate not pertinent to the answer.

The question is: does the machine:

  1. move to the right?
  2. move to the left?
  3. neither move left nor right?

Post your answer in the comments section below.


I received no solution to last week’s Quiz Question. Some explanation is in order. People need to realize some of these Quiz Questions are meant to appear difficult when they are not. This is one of them. All that is necessary to answer this is knowledge of basic physics. Here’s the explanation.

Know two things: Newton’s laws of motion and Einstein’s assertion of the equivalence of matter and energy. Here’s how it goes.

From Newton we know that, without an external force, the assembly pictured above will not move. That is to say, the center of gravity of the assembly pictured above will not move. That is critical.

Next, Einstein’s equivalence if mass and energy is exactly that. Matter and energy have the same properties. Energy, to an outside observer, behaves exactly like matter.

When energy is transfered from the battery on the right to the spinning flywheel, it’s the same as moving matter from the right side of the assembly to the left side.

Since the center of mass needs to remain motionless, the assembly will move to the right.


One thought on “Quiz Question

  1. Pingback: Quiz Question | Skeptical Analysis

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