Weightlessness on Earth?

One day, while Einstein was daydreaming at work, he imagined that a housepainter would experience weightlessness if he fell off a roof.

"If a person falls freely, he won't feel his own weight. This simple thought made a deep impression on me." - Albert Einstein

Objective:

This activity is a physical demonstration of Einstein's idea known as the "equivalence principle." This means that in a freely falling reference frame (that of the falling cup or person), gravitational effects will not be observed. Students will watch a demonstration of a falling cup of water with a hole in it. They will see that as the cup falls, the water stops running out of it.

Materials:

  • Basin
  • plastic cup with hole punched on its side, near the bottom
  • water

How:

  1. Using a pencil or pen, punch a hole into the side of the plastic cup, about a third of the way from the bottom.
  2. Place your finger over the hole and fill the cup with water.
  3. Holding the cup and water about chest-high over the basin, take your finger off the hole and allow about a third of the water to drain out. Point out to the students that gravity is pulling down the stream of water.
  4. Ask students to closely observe the cup and water for this next step. Drop the cup after a third of the water has drained. As the cup falls, the water stops flowing from the hole. Ask students why they think this happens. Explain that gravity is pulling on both the cup and the water, which means that they both fall together with the same acceleration.

A Little Deeper:

One on level, this is a simple demonstration of the concept of weightlessness in a freely falling reference frame. On another level, it illustrates the concept behind Einstein's Equivalence Principle, which states that, locally, gravity is equivalent to being in a accelerated reference frame; or, gravity and acceleration by an outside force produce the same effect on a local object (in this case, the cup).

Copyright © 2002 American Museum of Natural History. All rights reserved.

  • More About This Resource...

    • This activity, which introduces kids to Einstein's equivalence principle, uses a plastic cup with a hole in the bottom to demonstrate how the water stops flowing from the hole while the cup is in free fall.

      • The activity begins with a brief and engaging overview that introduces students to the science they are about to see.
      • Then, the procedure is laid out in simple step-by-step directions.
      • The activity ends with an explanation that gives students a deeper understanding of weightlessness and the equivalence principle.

    • Completion Time

      Approximately 1 period

    • Origin

      Educators Guide

    • Topic

      Astronomy

    • Subtopic

      Concepts

    • Subtopic

      National Science Education Standards
      Grades 5-8:
      Science as Inquiry CONTENT STANDARD A: 

      • abilities necessary to do scientific inquiry• understanding about scientific inquiry

      Physical Science CONTENT STANDARD B: 

      • properties and changes of properties in matter• motions and forces• transfer of energy

      History and Nature of Science CONTENT STANDARD G: 

      • science as a human endeavor• nature of science• history of science

      Grades 9-12:
      Science as Inquiry CONTENT STANDARD A: 

      • abilities necessary to do scientific inquiry• understanding about scientific inquiry

      Physical Science CONTENT STANDARD B: 

      • motions and forces

      History and Nature of Science CONTENT STANDARD G: 

      • science as a human endeavor• nature of scientific knowledge• historical perspectives

    • Learning Standard

      National Science Education Standards
      Grades 5-8:
      Science as Inquiry CONTENT STANDARD A: 

      • abilities necessary to do scientific inquiry• understanding about scientific inquiry

      Physical Science CONTENT STANDARD B: 

      • properties and changes of properties in matter• motions and forces• transfer of energy

      History and Nature of Science CONTENT STANDARD G: 

      • science as a human endeavor• nature of science• history of science

      Grades 9-12:
      Science as Inquiry CONTENT STANDARD A: 

      • abilities necessary to do scientific inquiry• understanding about scientific inquiry

      Physical Science CONTENT STANDARD B: 

      • motions and forces

      History and Nature of Science CONTENT STANDARD G: 

      • science as a human endeavor• nature of scientific knowledge• historical perspectives