New Scientist - USA (2021-11-06)

6 November 2021 | New Scientist | 55

Answers

Quick quiz #126

Answers

1 Nix, which is a moon of Pluto

2 It has evolved from a non-crab-

like form to a crab-like form

3 Electroencephalography (EEG)

4 William Whewell

5 Group 15

Cryptic crossword

#69 Answers

ACROSS 7 Bolete, 8 Icarus,

10/15 Hen of the woods,

11 Girolle, 13 Nylon,

17 Embalms, 20 Penny bun,

21 Apps, 23 Cilium, 24 Twitch

DOWN 1 Coca, 2 Teredo,

3 Keyhole, 4/9 Lions mane,

5 Mayfly, 6 Mushroom,

12 Isomeric, 14 Amanita,

16 Dunlin, 18 Agaric,

19 H-bomb, 22 Pact

#137 Tricky treaty

Solution

James gained one piece of candy

in the deal. There are two ways

in which the four children’s piles

of sweets could have differences

in size of one through to six:

(X, X, _, _, X, _, X), or the mirror

image (X, _, X, _, _ , X, X).

For example, if the child

with fewest got three pieces,

the two ways would be

(3, 4, 7 and 9 pieces)

or (3, 5, 8 and 9 pieces).

When taking them into one pile

and dividing that into four, the first

way will result in a remainder of

three sweets, the second in a

remainder of one. Since I took

three pieces and divided evenly,

we can deduce that it was the first

way. We know that James had

one more than another child,

so he had the second smallest

amount, and when the pieces are

averaged out, he gains one piece.

Tom Gauld

for New Scientist

Tied up

What is the best way to tie
shoelaces? Mine never stay
tied for very long. (continued)

Peter Martin
Belvèze, France
A simple method to keep
shoelaces from untying is to
wax them. Beeswax works best.
Just make a wad of it and rub it
into the laces, either round or flat.
It also keeps the laces waterproof
and helps them last longer.

Jon Hinwood
Melbourne, Australia
The trick of tying shoelaces
securely by wrapping an extra
turn around the other lace before
completing the loop is well known
to fishers. With a slippery nylon
line, four or five turns are used
to attach the hook. The technique
goes back to antiquity, with one
of the oldest extant examples
probably being the rope wrapped
around the horizontal spindle of
the winches used to raise a bucket
of water in a well.

This knot works by increasing

the contact surface between

one lace and the other, on

which friction acts. The friction

force also depends on the force

perpendicular to the contact

surface, which in turn depends

on the tension in the laces.

In the reef knot, the laces

are parallel, whereas in the

granny knot, the second loop

is perpendicular to the first, so

the laces cross instead of lying

alongside each other. This reduces

the contact area and the friction

forces. To pull a tight reef knot

undone, you can try pulling the

ends cross-wise as if it were a

granny knot, reducing the force

and allowing it to slip. This

weakness of the reef knot led to

the Scouts being taught not to use

a reef knot for critical applications.

Andy Bebington

Croydon, UK

Previous correspondence on

the topic of the best way to tie

shoelaces (2 October) discussed

two sorts of double knot, but

overlooked the thief knot. This

is like a reef knot, but the layout

differs in that the two “loose ends”

are on opposite sides; on a pure

reef, they are on the same side.

A thief knot was used for tying

up parcels when it was suspected

that the parcel might be broken

into. It was assumed that the thief,

when tying the parcel up again,

would automatically use a reef

knot, showing that the parcel

had been opened.

John Davenport

London, UK

The previous answers considered

only knots and the downstream

loose ends. But what is most

important is the tightness of the

upstream lace grid between the

holes. If the laces are tight here,

whatever form the grid takes, then

you only need a half knot and a

simple, easily undone bow.  ❚

“ A thief knot was used

for tying parcels when

it was suspected they

might be broken into.

It showed if the parcel

had been opened”