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 neutralise it. Then we wake up.
Birds sing dawn to dusk, so do they get tired in summer?
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.
Most birds, though not all, sing during the day, too, but this tends to be drowned out by traffic etc.
Street-lighting can confuse birds, causing them to sing in the middle of the night.
Why does fruit cake still taste fine after two years?
It’s
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 that’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 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 it’s impenetrable.
So
unless there is a manufacturing fault or damage to the oven, it’s
probably safe enough for you to stick your nose right up against the
glass.
Why do thunderstorms set off car alarms?
It’s 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.
Shock
waves can do more than set off car alarms — they can kill. Waves from
high explosives can make a skull distort, causing concussion and brain
damage. Many soldiers in World War I who were close to shell impacts
were killed, even though they showed little outward sign of damage.
Why does my nose run in cold weather?
To avoid a runny nose in cold weather, breathe in through your nose and out through your mouth
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 colours from deep red (cool stars, less than
3,000c) to bluish-violet (hot stars, greater than 30,000c).
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 colour. There are two main reasons why stars appear white.
First,
the human eye is poor at detecting colours 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 they’re 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.
How do candles that don’t blow out work?
They have magnesium incorporated into the wick.
For a flame to exist, it needs oxygen, fuel and enough heat to keep combustion going once it starts.
When
you blow out an ordinary candle, you extinguish the flame by removing
heat. You can still see the fuel — the wax smoke — coming from the wick,
but the ember in the wick does not supply enough heat to reignite it,
and so it will eventually go out.
But
magnesium catches fire at relatively low temperatures, so as it is
present in the wick, the heat from the ember is enough to reignite it.
Why do we like food we hated when younger?
As
we age, we progressively lose parts of our senses of taste and smell.
The first to go are those that make us dislike certain foods.
Much
later in life, we begin to lose the parts that allow us to enjoy our
favourite foods. In between is the golden age of the gourmet — enjoy it
while you can . . .
