Thursday, October 15, 2015

A video worth showing non-scientists

Sometimes I give talks about science to high school students and to community groups, mostly churches. Recently I showed this one.

Besides the "wow factor" I think it is valuable because it demonstrates some very basic but profound and important points about science.

1. Common sense observation and experience can be misleading.

2. Consequently, nature appears sometimes to be counter intuitive.

3. The way to discover the way things really are is by doing experiments.

One can explain the historical significance of this experiment. Aristotle advocated basing science on common sense observations [heavy objects fall faster, objects that start their motion eventually slow down unless a force is applied to them, objects on earth move in a qualitatively different manner to those in the heavens, ....]. In contrast, Galileo went against this and did real experiments, dropping two balls of different mass [probably not from the leaning tower of Pisa].

This can also lead to a discussion of how scientific observations today confront us today with many counter-intuitive realities such as wave-particle duality, Schrodinger's cat, dark matter, ....

For high school or introductory college students who know Newton's laws of motion and gravitation one can explain how this illustrates the equality of inertial and gravitational mass.

Aside. Thanks to insights from my wife, I stop the video before the very end when Brian Cox starts talking about Einstein and the Principle of Equivalence. Non-scientists find this too confusing, get fixated on it since it is the last thing they hear, and then get distracted from the more basic stuff such as the above.

If your game, you could then discuss the problems with string theory....


  1. I've never seen a feather bounce like that. Nice.

  2. They also did this on the Apollo 15 flight (youtube "Apollo 15 feather vs hammer".

    I remember being amused at my instinctive response: the hammer was too slow and the feather too fast!

    I also couldn't help but think of the "cost" of the experiment. They would have needed the hammer anyway and I think the cost of sending a feather to the moon was worth it.

  3. I use this video in first year classical mechanics class. It's really a terrific demonstration.

    What I like the most is the visible joy of Cox and the people in the control room, when they see with their own eyes what they (probably) all know ought to happen.

  4. It might be just the way they were set up for the drop, but it seemed to me that at the very beginning of the drop with air, they were accelerating at the same rate, as we would expect.

    Also, I was surprised to see any disturbance at all of the feather as it began to drop. I guess that was because there was tension in the fibres holding up the weight of each strand, and once there was no effective gravitational field, they went back to a neutral position.