A magician, in the one that usually comes to mind, uses an unrevealed trick to make something unexpected happen. There's skill on the part of the magician and often a sense of how people perceive things. Not being skilled at the slight of hand, I see another kind of magic - one that doesn't on a skilled trickster with a secret.
Most of you have played with that long, thickly coiled, floppy spring known as a Slinky. They're wonderful. You can make them walk down stairs, watch waves shoot back and fort, construct squirrel-proof bird feeders, lots of things. And you can perform magic - that second kind without skill or a secret.
I stand on a stool and hold one high above my head and let the bottom drop as far as it will go. I ask them to watch paying careful attention to the bottom.
"Three, two, one, drop!"
What they see doesn't make sense. For about a third of a second the spring's top drops like you would expect while the bottom appears to levitate in mid-air as the Slinky collapses down on itself. When the top crashes into the floating bottom the now compessed Slinky falls to the ground like anything else. I usually have to do this a few times and then they demand trying it themselves.
Some years ago I was on a flight to California with a bad case of speaker's block. In less than two days I'd be on stage at an animation company - a physics type talking to artists and computer science people. Sitting there at 35,000 feet I realized what I had prepared was pretty bad.
The sky was crystal clear and over the Southwest the talk I needed came to me. I'd talk about cartoon physics - the license good animators take moving objects around in the worlds they create. Seeing the Grand Canyoun suggested the Road Runner the Wile e Coyote. I scribbled a half dozen obvious things and had my talk before we landed. The next day I ran it by a few senior animators who helped me find some clips. All that was left was finding a Slinky. Someone had one in their office. I was set.
The talk started with the Slinky drop. It was doing exactly the opposite of what Wile e does when he suddenly realizes he standing on nothing but thin air high above the canyon floor. His ears remain fixed while his body falls. A Slinky is the un-coyote. Both break our idea of how Nature should work.. one is right, the other fantasy.
And a little epiphany a few years ago. I took Alan Alda's short course on science communication. He uses improv acting exercises to help people carefully listen to and establish trust with each other. A central idea of improv is "yes and.." - you accept what the other person has said and then expand on it. It's a powerful technique and in the hands of skilled actors can be astonishing.
It struck me the "hard" sciences like physics are different. Advances in physics come with "no and..." constructions. You see something that doesn't seem right - how a Slinky falls for example. It breaks your model of how things work. "No!" something's wrong with your model or your observation. You have to sort things out -- the "and" part. This is where discovery comes. "No and" has been a fundamental driver of scientific knowledge.
So what's up (or down) with the Slinky?
It's a simple pre-tensioned spring. Its natural resting state is where all of the coils are touching. Set it on its side and it's fully compressed. When you hold it up it stretches to where the pull of gravity exactly matches the upward tension of the coils. Release the top and the bottom just sits there as the top accelerates toward it. The upward pull from the tension in the spring keeps balancing out gravity. The bottom of the spring is the only part that wasn't deformed so it has no pull.
Working out the physics is a bit beyond first year mechanics, but if you have that under your belt it's fun. What you learn is the levitation time is depends only on the stiffness and mass of the spring. A standard Slinky has a 0.3 second hang time on Earth, the Moon, Jupiter or whatever.. Of course the center of mass of the Slinky falls exactly as if it were a point object.
For the record I've always liked the coyote more than the roadrunner. Inventiveness and perseverance no matter what.
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