Lithium ion batteries have
two electrodes sandwiching
a layer of flammable organic
solvent electrolyte between
them. Mobile phone batteries
are so slim that the gap
between the wide, flat
electrodes is tiny. In the case
of the Samsung Galaxy Note
7, manufacturing defects
squashed these electrodes
and allowed them to touch.
When that happens, the
battery short circuits
and creates lots of heat.
This speeds up the chemical
reactions, which generate
even more heat, leading to
a thermal runaway condition.
Lithium batteries can also
catch fire if they are
overcharged, or charged
below 0°C. This causes
lithium metal to build up on
the negative electrode, which
will also eventually cause
a short circuit. Protection
circuitry in the battery is
supposed to prevent this, but
this can also fail. LV
Why do phone
batteries
explode?
Although the great white shark has a fearsome reputation, in a straight fight, it is outclassed by the orca.
Not only are orcas much bigger, they are also smarter. Great whites are now known to be warm blooded
but orcas still have much higher metabolic rates because they breathe air. In the wild, orcas have been
seen preying on great white sharks.ORCA
GREAT WHITE
SHARK240,000 DAILY CALORIE INTAKE
vs
9m LENGTH 6m
5,600kg MAXIMUM MASS 2,200kg
48km/h TOP SPEED 40km/h
48 TEETH 40-56*
15,
* Exposed teeth at one time. Great whites have further rows of developing teeth behind the visible ones.- ATMOSPHERIC
COMPRESSION
At high speeds, it isn’t friction with
the air that produces most of the
heat, it’s the compression.
Like a ship moving through water,
you push a bow wave of air in front
of you. The air molecules can’t get
out of the way in time and they
bunch up, banging into each other
and getting hotter. Any parts of your
body facing into the wind will be
heated up. - HYPERSONIC
The best place to run would be
a long beach, like Pendine Sands
in South Wales, the UK. The air is
denser at sea level, which means
there are more molecules to
compress and heat up. Bodies are
typically cremated at around
1,500°C and aircraft research
from NASA reveals that you’d
need to be running at Mach 5
(6,000km/h) to reach that
temperature. - WRAP UP WARM
But that’s the temperature to
completely incinerate your
entire body – your clothes will
catch fire long before you
reach that point. Nylon has an
ignition point of about 500°C
and wool will catch fire at
230°C. Which means that,
with the right attire, you could
trot along at a leisurely
2,500km/h and still burst into
flames.
HOW FAST WOULD I HAVE TO RUN TO CATCH FIRE?
THE THOUGHT EXPERIMENT
HEAD TO HEAD
February 2017 19