英語時差：冒失的跌倒

Ya?l: It's time to go again to the A Moment of Science mailbag.

Don: A listener writes:

Dear A Moment of Science, I'm a big baseball fan, and I've always wondered why some players slide feet first and some slide headfirst. Does either way provide an advantage?

Y: Great question! And the answer depends on what sort of advantage you're looking for. If you want to be able to jump up quickly after sliding into a base, then feet first is best. But if speed is what you need, then headfirst might be better.

D: At least according to a thought experiment in basic physics. When a player slides, he's basically rotating around his center of gravity, located somewhere near the hips and waist. Slide feet first and the body rotates clockwise. Slide headfirst and the body rotates counter-clockwise.

Y: But because the arms are typically lighter than the legs, sliding headfirst creates a faster rotation, which should allow a runner to touch the base more quickly. Plus, sliding headfirst allows the runner to push off with his feet, providing an extra bit of momentum.

D: Now, the few studies to actually test this hypothesis have found no significant advantage to headfirst sliding. But the studies were small and don't prove that the headfirst technique isn't faster. It could have a lot to do with technique. Because coaches fear that sliding headfirst can lead to hand and finger injuries, many don't teach young players the art of the headfirst slide. Landing awkwardly before reaching base will slow you down.

Y: But when done properly, a headfirst slide might be faster.