Throw a pebble into a still pond, and the shockwaves from the disturbance will ripple out in all directions in nearly perfect concentric circles. But disturb the fine mesh of a window screen that’s soaked with rain or morning dew, and the shockwave will ripple out with a unique, four-pointed star pattern.
Backyard Scientist’s Kevin Kohler and BeyondSlowMotion’s Darren Dyk pointed a Phantom v1611 high-speed camera at a window screen that was freshly soaked with a garden hose, and then threw a block at it.
When recorded at 18,000 frames per second, which allows you to slow down the action, you can clearly see how the resulting shockwave is able to radiate outwards horizontally and vertically faster than it can diagonally. That’s because the shockwave’s energy can more easily travel in straight lines along the horizontal and vertical wires that make up the screen’s fine mesh. When moving diagonally, that energy has to zig-zag left and right, making repeated 90-degree turns as it navigates the screen’s fine grid pattern. The result is a unique star pattern that you’ll never see when tossing rocks into a lake.