Did You Know?

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Birds sing dawn to dusk, so do they get tired in summer?

Birds do sleep mainly at night, but only in very short snatches. They will also sleep during the day provided they feel secure enough, so the length of daylight makes little difference to them.

The main reason for singing is territorial. We hear them mostly at dawn because it is quiet and therefore the best opportunity to re-establish territories. Why does your own snoring usually not wake you up?

You snore most loudly when deeply asleep and hardest to arouse. Also, we live in bodies so noisy that we are equipped to ignore our own noises (such as breathing).

This sound cancellation enables us to sleep through our own snores. However, sometimes a violent grunt can break the rhythm of our snoring and our cancellation software cannot neutralize it. Then we wake up. Why does fruit cake still tastes fine after two years?

Its the high sugar content. Sugars are hygroscopic meaning that they draw water from their surroundings, including from any bacteria or fungi. This prevents growth of such microbial contaminants. Fruit cakes are also cooked for a long time, ensuring high temperatures through the cake, which means it starts out pretty much free of bacteria. Why does traffic jam up for no visible reason?

In open, free-moving traffic, each car can travel as fast as its driver wants to go. In denser traffic, there is interaction between vehicles, and if one car slows down then the one behind must also slow down. When the traffic reaches a certain critical density, a shock wave can spontaneously travel back through it. This is because when one driver brakes gently, the driver behind will choose to slow down more markedly.

The effect becomes more pronounced as it works its way back.

Meanwhile, new traffic keeps arriving at the same rate. With nowhere for it to go, it comes to a grinding halt.

The front end of the jam gradually clears, and when cars at the back finally get moving again, the road in front is virtually empty, and drivers wonder what the problem was. Why do sausages curl when they cook?

Sausage skin is mostly collagen, which shrinks violently as it is cooked. Most cooking equipment applies heat asymmetrically, causing uneven shrinkage, which creates curl.

Modern hot dogs do not have a collagen skin and so do not curl.

Is it safe to be close to a microwave oven when it's on?

We can see food cooking inside a microwave oven through the metal mesh incorporated into the glass of the door.This is because visible light has a wavelength of around 500 nanometres 5,000 times smaller than the holes in the mesh and so it passes through.

But the microwave radiation in ovens has a wavelength of around 12cm, roughly 60 times the size of the holes in the mesh, so its impenetrable.

So unless there is a manufacturing fault or damage to the oven, its probably safe enough for you to stick your nose right up against the glass.

Why do thunderstorms set off car alarms?

Its down to the speakers for your car stereo. Modern alarm systems use shock and pressure detectors.

The speakers act as pressure detectors. A speaker normally works by vibrating, according to the input of electrical signals, to produce sound. But the opposite can also happen: a loud sound or change in air pressure moves the speaker, producing an electrical signal that can trigger the alarm. Why does my nose run in cold weather?

This is caused by condensation and evaporation. When warm and moist exhaled air passes over the surface of nasal mucus that has been cooled by inhaled cold air, it condenses, just as it does if you breathe out on to a cold mirror.

The nasal mucus cannot absorb all the moisture, so the nose runs to get rid of the excess. The liquid running out of the nose is clear and clean condensed water, and is not a sign of an infection.

To avoid it: breathe in through your nose and out through your mouth. The sun is a star, so why is it yellow, not white?

Stars cover a wide range of colors from deep red (cool stars) to bluish-violet (hot stars).

Young, hot stars will be white, while cooler, older stars will be red. Our sun is a medium-sized star, burning at a medium rate. This is reflected in its yellow color. There are two main reasons why stars appear white.

First, the human eye is poor at detecting colors at low light levels. Second, many of the stars visible to the naked eye are genuinely white or bluish-white, being among the hottest and most luminous ones in our part of the galaxy.

Why do my legs wobble standing on a cliff top?

Standing on a cliff where there is no level ground in front of you to offer visual clues to help you avoid toppling, your legs keep over-correcting.That feels very insecure, which can make your knees shake.Plus, the impulse for legs to tremble when one is frightened seems a primitive one: small children commonly throw themselves to the ground when theyre afraid, in a state of helpless submission. Shaky legs might be part of that response. Why do we have ten fingers and toes?

Humans remote fishy ancestors emerged from the water with several bones from the wrist or ankle.These pioneers had lots of slender toes on all four feet too many and too slender for control and power.

By the time the first amphibians appeared, toes had thickened and been reduced to eight or so on each foot.

Long before the first reptiles evolved, five toes had become pretty much standard issue.

Specialisation tends to reduce the number of toes. Creatures that run, for example, need light feet so their toes reduce in number.Horses have just one toe. Some creatures, such as snakes, have even lost entire limbs.