Pics And Gifs: sport

Showing posts with label sport. Show all posts

4/05/2016

Why Golf Balls Have Dimples

It turns out, somewhat counter intuitively, those dimples significantly decrease the drag on the golf ball as it flies through the air, compared to a smooth ball. Not only that, but they also increases the lift somewhat. These two things combined can make the golf ball go as much as three times farther than the same ball without dimples.

The dimples on golf balls accomplish both of these things by creating turbulence in the layer of air around the golf ball, called the boundary layer. In simple terms, the dimples more or less scoop the air and direct it inwards towards the back of the golf ball. This effectively increases the net air pressure in the back of the ball, which reduces the drag by reducing the pressure pulling back at the ball from behind. This can reduce drag by as much as 50% over a smooth ball.

More technically, the streamline flow of air on a smooth ball separates fairly quickly from the ball as it passes over the surface of the golf ball, as seen in the image to the right. This ends up maximizing the size of the wake behind the golf ball, which maximizes the area of lower pressure, creating a large drag. With the dimpled golf balls, this streamline flow remains attached to the surface of the ball much longer which creates a smaller low pressure region behind the ball, thereby significantly reducing the drag on the ball.

The dimples also create lift when there is significant backspin on the ball as it flies through the air. This is very similar to how the seams of a baseball create lift when there is backspin. In both cases, the backspin causes the air to move faster backwards on the top of the ball, with the golf ball via the dimples and with the baseball via the seams. This creates lower air pressure above the ball than below, which creates a small amount of lift. A similar effect can also be observed with baseballs and golf balls when a ball has a certain amount of side-spin. Except, in this case, instead of creating lift upwards, it will cause the ball to tail to one side or the other, depending on the direction of spin. This is why balls with this side-spin will tend to travel in a sideways arc through the air.

You might be asking yourself, why don’t they then put dimples on planes, cars, and the like to reduce drag? Primarily because creating turbulence in the boundary layer doesn’t always reduce the net drag. It largely depends on the shape of the object and the speed at which it is traveling and things of this nature. In an object in the shape of a ball, where the primary drag is created by the wake, this ends up decreasing the net drag significantly. In more streamlined objects, such as an airplane wing, they create very little wake relative to the skin friction drag they experience. So the dimples wouldn’t help much and, indeed, creating this turbulence would actually increase the streamline drag, which would drastically increase the skin friction while not helping much with the less significant drag caused by separation in the wake.

Now, as far as cars go, which tend to not be all that aerodynamically shaped, relative to something like an airplane wing, it has been shown that creating a dimpled surface can decrease the overall drag somewhat on certain designs of cars. However, the difference in fuel efficiency is fairly marginal and hasn’t to date been shown to be near significant enough to warrant sacrificing certain cosmetic aspects of the car, namely covering it with dimples.

3/25/2016

Why do Olympians bite their medals?

sport 2:26 AM

According to four time Olympic medalist Summer Sanders, mainly because the photographers incessantly ask them to until they do it, usually at the end of the podium photo shoot sessions. The tradition probably stems from the age old practice of testing whether something was really solid gold or not by biting it.

Gold is a very soft metal, at least softer than tooth enamel, and if it’s fairly pure, you should be able to leave some teeth marks in it by biting it. The practice of biting precious metals also allowed people to see if perhaps the gold object was really just gold plated, with something like lead at the center. If so, the gold plating could be scraped off with your teeth and, given the often bitten gold coins weren’t that thick, the plating tended to be fairly thin, so you didn’t have to bite too hard to discover whether it was relatively pure gold or not.

Obviously Olympic gold medals today are not made of solid gold (not since 1912, though they do have 24k gold plating). Rather, the gold medals are made mostly of sterling silver. But were you to actually bite down on the gold plated silver Olympic medal, you should be able to make a dent as silver is also softer than tooth enamel, but harder than gold.

Using Mohs mineral hardness scale, we see that tooth enamel is rated at a 5, while gold is rated at around 2.5 and silver at a 2.7-ish. Tooth enamel is also higher on the scale than copper, which the “bronze” Olympic medals are mostly made of, so it’s possible to make teeth marks on those too.

Mohs hardness scale is a relative hardness scale created by German geologist Friedrich Mohs in 1812, rating things based on scratching one material against another, the one that makes a mark on the other is rated as harder. If both scratch each other, they are considered to be the same hardness.

For reference, glass is rated at 5.5 and tooth enamel is actually slightly higher than steel or platinum (at 4-4.5). (Note: just because something is only slightly higher on this particularly scale than something else doesn’t necessarily mean it’s only slightly harder. For instance, diamonds are rated at a 10, while corundum is rated at 9, but diamonds are 4 times as hard as corundum. Further, corundum is twice as hard as topaz, which is rated at an 8.)

Despite the fact that none of the athletes are actually trying to make marks on their medals or checking for authenticity, the tradition with Olympians has endured and photographers simply won’t let it die as it makes a more interesting, “playful” shot over an Olympic medalist simply holding their medal up next to their faces or the like.

Why are the Olympians wearing colored tape on random parts of their bodies?

sport 2:23 AM

The colored tape the Olympians and other athletes wear is called “Kinesio® Tex Tape”, which is essentially just an elastic cotton strip with an acrylic, heat activated adhesive.

The tape was designed in the 1970s by a Japanese chiropractic and acupuncture specialist, Kenzo Kase. To date, there hasn’t been a single study to conclusive show that this tape actually does anything the makers and athletes claim it does, though as Kevin Anderson, director of Kinesio UK, states “There’s a lot more needed on the research side to confirm the positive results we’re seeing so far.” (In fact, there have been numerous studies in the over 30 years it’s been around and so far the results of using the tape have been more or less in-line with the placebo effect. It’s interesting that the company itself can make such claims when they apparently have not done research themselves to back them despite being around for over 30 years; otherwise, I’d assume Mr. Anderson would be citing said research, rather than saying research is needed.)

So to answer your question as to why Olympians and other athletes are wearing colored tape – because they think it helps in some medically significant way. The lack of evidence to support this never stopped athletes from wearing Phiten bracelets/necklaces or Power Balance holographic bracelets, which in their heyday both got amazing reviews from athletes as to the performance benefits, only to go out of fashion when it was conclusively shown that they didn’t do anything (and when the sponsorship dollars to said athletes dried up).

So it’s not surprising that Kinesio tape has become popular; it certainly seems more believably beneficial than an over priced plastic bracelet with a holographic sticker on it. Further, the placebo benefit is potentially better than nothing. Basically, if nothing else, it’s probably good in such athletic competitions to think you have a slight edge… the power of positive thinking and all that. As Amy Powell, associate professor of sports medicine at the University of Utah School of Medicine said in a recent interview, “Anything that [athletes] perceive as an edge, they’ll try, whether it’s scientific or not. And the athletes are convinced that [Kinesio tape] is really helpful. It wouldn’t be the worst placebo in the world; it’s not doing any harm.”

As mentioned, this tape has been around for a while, even seen in the Olympics since 1988, but has only recently become widely popular among athletes after Kinesio very wisely donated 50,000 rolls of their tape to be used by various Olympians from 58 countries during the 2008 Olympic Games. They also switched gears from primarily offering skin colored tape to pushing colored tape. They say on their website, “The colors were developed to be compatible with color therapy…” And, more accurate and surprisingly candid, they go on to state the colors were made to “provide field advertising at athletic events, a conversational opener, and instant product recognition.”

According to sports chiropractor and strength and conditioning specialist, Chad Peters, they also “paid [Olympic volleyball player] Kerri Walsh to wear black tape instead of flesh tones in Beijing. After that, it just exploded. Everybody wanted it.” Specifically, after the Beijing games, sales skyrocketed to 300% of what they were before and Kinesio tape has become “must use” by athletes the world over.