Page 62 - How It Works - Book Of Amazing Answers To Curious Questions, Volume 05-15

What are Why do we

black box change the clocks

flight recorders during the year?

made from? t was originally suggested in Britain by

I William Willett in 1907, to avoid wasting
the daylight during the summer when the

ockpit flight recorders are enclosed in a
C steel or titanium box (which is painted Sun normally rises long before anyone gets
orange to make it easier to find). Inside that out of bed. The idea wasn’t tried until 1916, a

there are some racks of very rugged year after Willett’s death. By that time
electronics, but most of these don’t actually Britain was at war and lighter evenings
need to withstand a plane crash, as long as allowed the government to save fuel and
the tapes or memory chips containing the money on lighting. At various times in the
actual data do. They are stored in an inner 20th century, Britain has experimented with
armoured steel case coated in a fl ame double summer time, and staying one hour
retardant paint and lined with several layers ahead of GMT all year. Lighter evenings in
of insulating materials. Blocks of paraffi n summer result in fewer road accidents
wax are used at various points as thermal overall, but winter mornings would be very
barriers. In a fire, the paraffin melts and dark if we didn’t move the clocks back again.

absorbs some of the heat.
How do noise-

cancelling

headphones

work?

ll sound, whether music or general
A background noise that interferes with
our music, is compression and rarefaction of
the air around us. Noise-cancelling
headphones work thanks to the materials
they are made of, which block out unwanted
Can gas be a noise. Passive noise-cancelling headphones, How exactly
such as circumaural headphones, maximise
conductor of noise-filtering properties by being packed do vacuum

full of sound-absorbing material, such as
electricity? but blocks out interfering noise, such as that flasks work?
high-density foam. This makes them heavy,
of an engine. Active noise-cancelling
ases are generally poor conductors of headphones go a step further and actually eat can be transferred in three ways:
G electricity. Good electric conductors, erase lower-frequency sound waves. They H conduction, convection or radiation.
such as metals, have loosely bound contain a tiny microphone that listens to the Conduction involves atoms physically
electrons that can move freely when ambient noise. Their internal electronics colliding with each other to transfer their
exposed to an electric potential, producing a measure this and create a noise-cancelling kinetic energy. Convection does this too, but
current. Gases have no free electrons and wave that is 180 degrees out of phase with also takes advantage of the fact that hot
therefore do not conduct electricity easily. the intruding waves, or ambient noise. This fluids have lower density and so will rise,

Under a strong enough electric potential or wave cancels out the annoying taking their heat with them. Vacuum fl asks
in extreme heat, gases can, however, ‘surrounding’ sounds without have a double glass wall and the gap in the
become ionised, breaking apart into charged erasing the audio that you middle is a vacuum. This means it contains
ions and electrons to create a different state want to hear through the no atoms that could transfer heat across the
of matter known as plasma. This occurs, for headphones. These gap by conduction or convection. That
instance, during a lightning strike or inside a headphones can reduce leaves radiation, but the sides of the glass
neon light. Unlike gases, plasmas are good noise by a further are also silvered, which helps to refl ect
conductors of electricity. 20 decibels. radiated heat from either side.

62 How It Works