BACK TO THE FUTURE, AGAIN conservation of angular momentum? They shouldn't have to wait for it to come around in high school physics class." "Do we get flung off this exhibit?" I had to ask. "No, this one demonstrates something a little more subtle. It runs at a constant speed, and it's big — 12 feet in diameter — and has a view screen around the perimeter of the rotating platform that blocks the view of the outside world from inside the carousel. That way you don't get a visual sense that it's rotating. It's also powered, rotating at a speed calculated to demonstrate Coriolis acceleration without making people seasick." When it was our turn, and the device was stopped, Lee opened one of the gates through the view screen and we climbed aboard. "Sit on one of the low cushions so you can't see outside the carousel," Lee advised. Then I pressed the "start" button, and the carousel began to rotate — but with no visual indication that we were in a rotating frame of reference. "It's easy to forget that we're spinning," said Lee. "That's the idea." Lee picked up one of the soccer balls and rolled it over to me from across the carousel floor. The ball veered to the right, as if by magic. "Maybe the floor isn't level," I said, so I rolled the ball back toward Lee. But it still veered to the right, which was now in the opposite direction. Then we tried hitting each other with a thoughtfully-provided Nerf gun. We
The Land Yacht Experiment Table. Perfect for skeptics who need to be convinced that yes, a sailboat really can sail into the wind. Adjusted carefully, these models can point within 30 degrees of the true wind direction.
always missed: The soft projectiles veered to the right just like the soccer balls. "What happened to Newton's First Law of Motion?" I asked. "According to Newton, an object moving in a straight
The Virtual Wind Tunnel. Adjust airfoil parameters, or draw your own sail shape, and check out lift, drag, and the effects on other nearby foils or sails.
line should continue to move in a straight line . . . unless it is compelled to change that state by forces impressed on it," Lee finished Newton's law for me. "In this case, like, no force was applied to the moving objects — yet they followed a curved path!" This was Coriolis acceleration in action, the dynamic effect that pulls moving objects to the right when viewed in a counterclockwise rotating reference frame. The counterclockwise rotation models the Earth's rotation in the Northern Hemisphere. "To resolve the paradox," Lee explained, "we can check out the view from the video camera on the ceiling, fixed in position. It will be easy to see that the balls or the Nerf projectiles are not curving at all. They are still going straight, viewed in a non-rotating frame of reference, and Newton was like, right after all. But the rotation of the frame of reference inside the carousel produces the illusion of a pull to one side. This is the same force that causes high-pressure weather systems, with air flowing away from a high-pressure center, to rotate clockwise, and low-pressure storm systems, with air flowing toward a central low, to rotate counterclockwise as January, 2020 •
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