Wendy Sadler - Why Do Golf Balls Have Dimples?: A Book of Weird and Wonderful Science Facts

Chapter 1: Sport

Can bungee jumping make your eyes fall out?

Bungee jumping is surprisingly safe, with only a handful of deaths reported since the sport began in 1979. But damage to the body is pretty likely because of the huge forces on you when you reach the bottom of the jump. In a bungee jump youre falling at very high speed and then get stopped and pulled back up very suddenly by the elastic reaching the end of its stretch. This change in direction makes some parts of your body want to carry on moving down, whilst others are pulled back up by the bungee rope. Sounds painful already

Now for the good news. Your eyes are fixed into your skull by six muscles that make your eye move up and down and left and right. Your eyeball also fits very tightly into the socket of your skull. So it is pretty difficult to dislodge an eye completely even by sneezing with your eyes open (but that is another story!).

There have been tales of people losing their eyesight after a bungee jump, though so whats happening? Well, when you reach the lowest part of the jump the blood in your body gets pushed down to the bottom end of you all at once. As you are upside down, this means blood rushes to your head and your blood pressure goes up a lot. This can have a few nasty side-effects that you might want to consider before leaping from that bridge.

There is a part of your eye called the retina which we use for seeing colours and light and dark. If the blood pressure in your eye gets very high it can make this retina come loose, and a loose retina can mean that the signals from your eye to your brain get mixed up. You may start to see flashes of light or strange floating shadows in front of your eyes. This can usually be put right if you get to a doctor quickly enough, but if not it can give you permanent damage. So in short, your eyes wont fall out, but, if youre unlucky, they may never be the same again.

Why do golf balls have dimples?

In the beginning, golf balls were smooth. But then golfers began to notice that the older and rougher the balls got, the further they would fly. The old scuffed-up balls were in big demand, though no-one really understood what was going on.

Common sense would suggest that smooth things should cut through the air more easily. Cars and boats that are designed to go as fast as possible usually have smooth surfaces and streamlined shapes. The force that slows things down in air is called drag, so how come a rough ball would give you less drag?

When a smooth ball travels through the air, the air flowing around it doesnt meet up nicely at the back of the ball. The path of air over the top and the path underneath split up and create an area of turbulence behind the ball that slows it down. But if you take a ball with a rough surface, the air flowing around it sticks to the ball longer until the air almost meets up again neatly at the back. The fact that the air doesnt split so early on means there is much less drag at the back of the ball. This in turn means it isnt held back and flies much further.

The shape, pattern and depth of the dimples can make a difference, too. Most golf balls have round dimples, but some now use hexagon shapes which make the drag even less. The dimples are usually arranged in a pattern that is the same all over the ball but in the 1970s one company made golf balls with a special design where the dimples were deeper in some parts of the ball than in others. This helped the ball correct itself in flight. These were banned from use in competitions but can still be bought for private use if you need a bit of help on the golf course! If you ever find yourself with too much time on your hands you could try counting the dimples in your golf ball to see where it was made. American ones have 336 and British ones have 330!

Is it safe to sneeze when you are driving?

You know the dreaded burning feeling up your nose which tells you a sneeze is about to happen? And the more you think about it the less likely it is to go away? Add this to the fact that you are driving down the motorway at top speed. Are you about to put your life (and others) at risk?

Lets work out what might happen. Although any distraction can be dangerous, the biggest problem with sneezing is that your eyes will be closed generally not a good idea when driving! If we guess that a sneeze lasts about one second we can work out how far you will actually travel when going 70mph and its about 31 metres (or 101 feet).

This is about six car-lengths, so certainly enough of a distance to cause problems if you are on a fast-moving road, or something changes unexpectedly. What makes accidents less likely is that you can prepare for a sneeze. You usually get a good few seconds warning and this lets your brain take into account what is happening around you to help you prepare.

So, to prevent any danger, could you train yourself to keep your eyes open when you sneeze? Unlike what you may have heard, your eyeballs will not pop out if you sneeze with your eyes open. Scientists dont fully understand why we close our eyes when we sneeze. It isnt to protect our eyes from the germs coming out of our noses, as they are fired out at high speeds of up to 100mph! A few people can keep their eyes open when sneezing but for most of us the blinking is what is known as a reflex action. We just cant help it. Its the same type of thing that happens when you tap below your knee and your leg kicks up. It just does. However hard you try, it isnt something you can learn.

The other thing you could do is if you feel a sneeze coming on, is to press firmly either just under your eyebrow, or against your top lip. The signals that go from your nose to your brain pass by both these areas of your face. If you do it quickly enough you may be able to prevent the sneeze for a little while, perhaps even long enough to pull over somewhere safe

Why do you spin a rugby ball?

When rugby began as a sport they used to use a pigs bladder wrapped in leather. The bladder had to be inflated by someone blowing into it with their mouth not the most popular job in town! The shape of the ball is a really important part of the sport. Compared to a round ball, it is easier to carry under the arm, easier to pass and because it doesnt roll so far the ball stays in play for longer. But there is another advantage to the shape that, when used correctly, can help make you a better player.

One problem with an oval shape is that when you throw it through the air, any wobble that it has makes a lot of drag, which slows the ball down. If you watch a good rugby player throw a ball, you will see that they twist their hand as they throw. This twist makes the ball spin like a corkscrew as it flies through the air. The idea of the spin-throw is to stop the ball wobbling so that the ball can travel a lot further. But why does the spin make the ball more stable in the air?

If youve ever been on a bike you will have noticed that it is difficult to stay upright when the bike is going slowly but as you go faster it gets easier. This is because of something called the gyroscope effect. The spinning of the bike wheels create a force that makes the bike less likely to fall over. You may have seen small gyroscope toys that can balance on your finger or on a tiny point for as long as they keep spinning, but, as soon as they stop, they fall over.

The spinning of the rugby ball does the same thing. It keeps the ball lined up in the same direction as it flies through the air, and with less wobbling you get less drag, so the ball has more chance of making it over those all-important bars.