Spin

What is it about spin that is so fascinating? Why do we love to spin things and what is spin? Evolution designed our hands with fingers and an opposing thumb to make spinning an easy action. Flicking the thumb against the middle finger can summon immediate attention. It can also twirl a dart, which travels more accurately towards its intended target. A gyroscope is stable until it stops turning.

It was a crucial moment in the England vs Ukraine football match. Kyle Walker had the football in his hands, pondering where to place the throw-in. He whirled the ball in his hands. He spun it again as if to settle his mind with the distraction of the ball’s rotation. And again, he spun the ball in the air. He had made up his mind. He threw it in and the game resumed.

Spinning.

In other sports, we see Roger Federer spin his racquet as he prepares to make or receive a serve. It must help him concentrate and he is not alone. So many tennis players of all abilities do it.

In cricket, leg-spinner Shane Warne’s first test ball in England in 1993 bamboozled Mike Gatting at Lords – the centre of the cricket universe. Hailed as the ball of the century, it changed direction on hitting the pitch and hit Gatting’s of stump. Ominously spinners spin the ball from hand to hand before starting their run up to bowl. Bowling at a slower speed, they deceive batsman by the very act of flicking the ball with their wrist or fingers as they release it, which will make it change direction on pitching.

Back with football, Kyle Walker can curl the ball, crossing it into the penalty area or even into the net by spinning it with the action of his boot sliding across the football to make it spin.

Spinning.

Kids do it with coloured tops which became white when they spin them. We all do it at various times. The spin of a ball has been quantified by mathematicians using the concept of angular momentum (L). Every A-level mathematics or physics student must remember it as being proportional to moment of inertia (I) and angular speed (ω) measured in radians per second.

L = I ω

But angular momentum has psychological as well as mathematical attributes. The act of spinning something calms, settles the mind, and distracts us from everyday cares.

Spinning

Spinning an electric current creates a magnetic field used practically in the electromagnet which can open doors or lift scraps cars. Conversely spinning a wire in a magnetic field creates electricity – the electric motor – which will power all sorts of devices including electric cars. So spin has bizarre properties.

Spinning

At the atomic level, electrons fill orbitals around the atomic nucleus but these electrons have a function labelled as spin and they can have similar or opposite spins. In 1945, Wolfgang Ernst Pauli received the Nobel Prize for his discovery of a new law of Nature which involved the idea of the spin of an electron (defined as up ↑ or down ↓) being a basic aspect of the structure of matter. So spin is pretty important.

Spinning

At the other extreme spin affects moons, planets, galaxies even the universe itself.

Astronomers have for centuries speculated about the dark side of the Moon, the second brightest object in our sky might. For billions of years it has been impossible to see the dark side from Earth because both the Earth and Moon spin and this causes a spinning phenomenon known as tidal locking. As the Moon orbits around the Earth, the gravitational interactions between the two bodies have subtly alter their orbits and the speed at which they rotate.

As the Earth is much larger than the Moon, the Moon’s rotation is slowed down until it reaches a balance point. This balance point is where the time for the Moon to have a full rotation around its axis, is the same as the time for the Moon to fully orbit around the Earth, becoming ‘tidally locked’. This means that the same portion of the Moon always faces towards the Earth, and we can never see the dark side.

A neat NASA animation shows this.

Spinning

But spin exists on an even greater scale. Our Milky Way galaxy of millions of stars is seen as a spiral and consequently spinning mass. More recently scientists have detected the collision of a neutron star and a black hole. (Simulation here). Like a moth to a flame the neutron star spirals to the destruction attracted by the irresistible gravity of the black hole.

Spinning.

An everyday action which permeates our lives in so many subtle ways.

By the way, Kyle Walker’s spinning of the football must have helped, England beat Ukraine 4-0 and Roger Federer won his match at Wimbledon.

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