Grass Tennis Courts Are Faster? Why?

Factual Questions
1

Just finished watching the great Wimbledon Men’s Singles final, where Goran Ivanisovic won with 20+ aces. The commentator mentions that “grass courts favor hard servers like Ivanisovic, because they’re so fast.”

I’ve heard this before, but it still puzzles me. By “fast” I presume they mean the ball bounces off the court with the least depreciation in velocity, which I figure would come from bouncing off a harder surface than a “slow” court. Same as how a superball bounces harder off concrete than a wood floor.

So why would grass, which is packed dirt with a cusion of tiny leafy blades, be “harder” and “faster” than clay or asphalt? Am I looking at the physics all wrong? Does grass have some sort of “bounce” effect from its softness? Does the precise squishiness or texture of the ball have something to do with it?

Any insight or good guesses apprciated.

2

The ball skids

3

But here’s a little more detail. :slight_smile: A tennis pro’s serve has a lot of topsin, much more than any ordinary shot. On a hard court, when the ball strikes the surface, it ‘catches’ a bit, slowing the spin as well as the ball, and causing it to rise faster. This slows the ball a bit as it gives up kinetic for potential energy, and also makes it an easier return target as it’s higher when it reaches the returner. On grass, the ball stays low and fast, which makes it very hard for even the best player to get a solid return. Ultimately, this is why so few players have ever won a Grand Slam-the grass courts at Wimbledon favor the serve-and-volley style players, while those same players get eaten alive on the clay courts at the French if they can’t adjust their style to fit the conditions.

OK?

4

I’d like to nitpick the physics a bit if I may :wink:

Grass being faster is a combination of a couple of things.

The first is friction. “The ball skids” is correct, but to explain in more detail…on a “slow” surface like concrete or clay, when the ball contacts the surface the friction induces spin on the ball, robbing it of some of its speed. To explain it in pure physics, the linear kinetic energy is translated into rotational kinetic energy. So the ball comes off of the concrete surface with a significantly lower velocity than it had before hitting the surface, but with a higher spin. On grass, this effect is lessened, so the ball holds more of its velocity as it comes off the grass.

Another effect is the elasticity of the surface that the ball is hitting. When a ball hits grass, some of its vertical momentum is lost as energy is absorbed by the grass as it compresses, and the dirt underneath as it yields slightly. Concrete or clay on the other hand, is more unyielding and the ball loses less energy as it bounces off the surface. The collision is more elastic. So to a tennis player, a ball coming off the grass also has a much lower bounce, making for less time to react to return the shot (a low angle path has a higher horizontal velocity than a high angle path, even when the balls are travelling at the same speed. Trigonometry angles/vectors).

So, both of these factors combine to make grass a significantly “faster” court to play on. So much so that after playing a long time on concrete, if I play on a grass court the ball seems to “shoot” off the ground.