54 | New Scientist | 5 October 2019
Freewheeling
I rapidly lose my balance if I try to
ride my bike with no hands, but I
can easily ride it when the tip of
just one finger is lightly touching
the handlebars. Is that finger
providing significant support or
do I just believe that I can’t ride
a bike no-handed?Matt Chamings
Barnstaple, Devon, UK
When a bike is in motion it doesn’t
just fall over because the spinning
wheels act as gyroscopes, which
maintain their orientation. The
front wheel only turns, and
potentially unbalances the bike,
if the rider leans to one side.
So riding a bike with no hands is
easy as long as the rider stays fairly
still. Pedalling shifts weight from
side to side, so freewheeling is
easier. Keeping one finger on the
handlebar is comforting but not
absolutely necessary. Possibly
the rider becomes anxious when
removing the finger and shifts
weight by tensing up. So yes,
unbalancing could be down to
lack of belief or confidence.Peter Peters
Sherborne, Dorset, UK
More active than the gyroscopic
effect in keeping a bike upright is
the so-called trail effect, in which
the line of the steering axis – from
the handlebars down the front
forks to the ground – intersects
the road ahead of the point where
the tyre makes contact. But both
effects are small and usually
augmented by the rider applying
a light torque to the handlebars.
The third effect is shifting the
position of the rider’s centre of
mass. This is very effective when
riding no-handed and has to be
learned. Unless our rider has a
physical difficulty, he can teach
himself to ride no-handed in spite
of any inhibition resulting from
earlier failures.Peter McPherson
Merriott, Somerset, UK
I have often wondered why with
some bikes I can ride no-handedwhereas on others, I have to
quickly re-grasp the handlebars.
I came to the conclusion that
it is due to the front wheel not
being able to function properly as
a gyroscope if the bearings in the
front fork are a bit tight. When
riding with no hands and with
well-fitted bearings, any slight
tendency to lean from a vertical
posture causes the front wheel to
turn slightly in the direction of
lean, thereby replicating what
happens when you corner. But
stiff bearings slightly resist that
turn of the wheel and balance is
lost. The questioner, with his
single finger on the bars, is simply
overcoming the reluctance of the
stiff bearings to turn.Philip Taylor
Buckland Dinham, Somerset, UK
When a bicycle is travelling
slowly, it needs greater steering
correction to maintain balance,
hence it tends to wobble at
slow speed. The trick to riding
no-handed is to have sufficientgrip on the saddle and pedals to be
able to steer the bike, and so cause
the front wheel to turn one way
or the other. If not, one finger
on the handlebar will enable you
to microsteer and stay upright.
Unicycles are balanced in
the same way, by turning the
single wheel via the saddle.
Imagine trying to ride a bike
with a non-steerable fixed front
wheel. You would quickly crash
down on one side or the other,
it being impossible to balance
such a machine.Hilary Johnson
Malvern, Worcestershire, UK
As well as physical or
psychological support, the
finger on the handlebars may
be providing feedback to help
the cyclist adjust their balance.Time and tide
What is the smallest body of water
that is influenced by the moon’s
gravitational pull?Chris Hughes
Professor of sea level science,
University of Liverpool, UK
Every body of water is influenced,
but the effect is much harder to
see in smaller ones.
The smallest body of water
in which lunar tides have been
measured is Loch Ness in the UK,
which is 37 kilometres long. Here,
the tides have an amplitude of
about 1.5 millimetres.
Tides result from the small
differences in the moon’s
gravitational attraction from place
to place on Earth. In water, this
results in differences in surface
height up to about 0.8 mm for
points 10 km apart. Ocean tides
are much larger than this suggests
because the pull oscillates about
twice a day, close to the time it
takes water to slosh naturally
around ocean basins, producing
a resonance effect that amplifies
the rising of the water. In smaller
basins such as the Mediterranean,
or lakes, this effect is weaker.
Another factor is that land is
also pulled up by the moon, and
these combined effects would give
a tide of 0.45mm in Loch Ness. But
the tide there is bigger than this
because the weight of water in
the surrounding seas plays a role.
High tides push down on the UK
coast and cause Loch Ness to tilt
from end to end. Most of what is
measured as a tide is the result of
this tilt – the land moves more
than the water. Disentangling
these effects is very tricky, so it
is hard to tell whether the moon
affects a small body of water. ❚This week’s new questions
Hourglass figure Why do wasps have such a narrow waist?
What could be the advantage of having such a narrow join
between thorax and abdomen, which seems like a very weak
point? Rosalind Coles, Clyro, Powys, UKNeeding focus I wear spectacles to correct for myopia and
astigmatism. Is it possible to create a program to adjust
the image of a TV, mobile or PC monitor using my optical
prescription such that I could view it without spectacles?
Mike Daw, Cheltenham, Gloucestershire, UKWant to send us a question or answer?
Email us at [email protected]
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GAIN/GETTY^ I
M^ AGESWhy do wasps have such
a narrow join between the
thorax and abdomen?