54 | New Scientist | 11 June 2022The back pages Almost the last word
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Full terms and conditions at newscientist.com/lw-termsSliding scale
In children’s playgrounds, I am
always confounded by how the
slipperiness of the same slide can
vary hugely throughout the day,
and on different days. What
factors influence this?Rob Wheway
Children’s Play Advisory
Service, Coventry, UK
Speed differences of children
going down playground slides
is primarily due to the clothes
they are wearing. Synthetics
(nylon/polyester) give a faster
speed than cotton/denim. The
speeds can range between too
fast for safety (very occasionally)
and too slow to be fun.
The seasons, weather and time
of day will determine the clothes
worn rather than having a direct
influence. The size and weight of
a child doesn’t appear to have a
significant effect.
Some slides become too
slow within a year and need to be
polished to bring back their utility.
This is probably due to a build upof rubber scuffing from soles
of shoes, but I can’t be certain.
When consulted on
playgrounds, children and parents
request bigger and faster slides,
which demonstrates that slides
are still popular and that people
today aren’t risk averse, as is
commonly supposed.Stuart Reiss, via Facebook
There is a formula for this.
MICCF × FR (Melted Ice Cream
Cohesion Factor multiplied
by Fabric Resistance).Geoff Convery
Lincolnshire, UK
Most, if not all, of the difference
in slipperiness of children’s slidesMAGDAL
ENA^ BUJAK/ALA
MYwill be due to the amount of water
on their surfaces.
Ambient humidity varies
greatly, both day to day and over
the course of the same day, and
this will affect the amount of water
on the slide. Early in the morning,
humidity tends to be higher and
the temperature lower, so any
given slide will probably be quite
wet. If it is warm and sunny, the
water will evaporate.Chris Szymonski
Waupaca, Wisconsin, US
The tribology, or “slipperiness”, of
playground slides is a function of
temperature, relative humidity of
the air, the material of the slide
and the fabric of children’s clothes.
A very thin layer of water covers
surfaces. This can act as a lubricant
if the clothing worn by the slider issynthetic and water-repellent,
but not if it is hydrophilic and
water loving, such as cotton.
There may be more water
on the slide on a cool, humid
morning than on a sunny
afternoon. In addition, older
slides made of zinc-passivated
steel are more hydrophilic than
newer slides made of plastic.@throwatwitfit, via Twitter
The answer depends on how much
sunscreen little Freddie’s mum
slathered him with today.Katherine Rose, via Facebook
The weather and clothes have a
big impact. One surprisingly fast
slide run occurred on a damp day
when my daughter was wearing
waterproofs. It was so fast that she
shot off the end of the slide. Wethink that the water built up in
a layer between the slide surface
and the waterproofs, making the
combination extra slippery.Mike Follows
Sutton Coldfield, West Midlands, UK
The presence of water can change
the coefficient of friction between
two surfaces. I slipped over on
a steep grassy slope during a
downpour while wearing a
waterproof jacket and trousers.
Much to the amusement of
friends, I ended up sliding
a considerable distance.
The waterproof material
had become separated from the
grass underneath by a thin layer of
water. This is the same mechanism
that causes a vehicle to aquaplane.
It might have been a different
story if I hadn’t bothered putting
on my waterproof overtrousers.
The water would have been
absorbed by the rougher
hydrophilic fabric of my walking
trousers and this might have
ensured contact (and friction)
between the two surfaces.Lesley Clayton
Truro, Cornwall, UK
If you lived in Trowbridge, a town
in the UK, and you were a child in
the late 1940s, the answer to this
question would be that it was
slipperiest around late morning
to lunchtime. This is because the
margarine that my mother and
her sisters applied to the top of the
slide first thing in the morning
would, by then, be coating the
whole length of the slide.Off the boil
Why does taking a near-boiling
saucepan of water off the hob
immediately cause a lot of steam
to be released from the water?Chris Evans
Earby, Lancashire, UK
The questioner is confusing
steam with a mist of waterThis week’s new questions
Peas in a pod Peas are in the dark inside a pod, so can’t use
their chlorophyll for photosynthesis. In which case, why are
they green? Anthony Woodward, Portland, Oregon, USHiccup hiatus Holding your breath while pinching your nose
is supposed to stop hiccups, but does anything actually cure
hiccups? Jill Lucas, Huddersfield, West Yorkshire, UKIf peas grow in a dark pod
without light, why are they
coloured green?“ One surprisingly fast
slide run occurred on
a damp day when my
daughter was wearing
waterproofs. She shot
off the end”