# Executive desk toys explained

I’ve been collecting unusual toys, gadgets and puzzles for almost two decades. Due to my interest in science, most of them incorporate some sort of scientific principle. Let’s look at two of my favourites.

Most people are familiar with Newton’s Cradle: four or five steel balls suspended by wires from a frame. If one of the balls at either end is raised and released it will swing back to its original position and strike the remaining balls in the row. This causes the first ball to stop, while the ball at the opposite end of the row swings up. This action repeats itself until the apparatus winds down and stops over the course of a minute or two.

The action is hypnotic and elegant. The cradle rocks with a predictable rhythm that is mesmerising to behold.

The executive toy illustrates the principles of conservation of energy and conservation of momentum. Imagine a Newton’s Cradle with only two balls. Raise and release one of the balls. The momentum in the first ball is “lost” when it strikes the second ball. The first ball comes to a near-immediate stop. However, the laws of physics don’t allow that momentum to vanish – it has to go somewhere. So the second ball is knocked into the air and will travel to almost exactly the same height from which the first ball was released. That’s conservation of momentum in action. The reason the second ball doesn’t travel to exactly the same height as the first ball is because some of the energy escapes as friction due to air resistance as well as a tiny amount of heat that is generated on impact. The total energy in the system, as well as the momentum, is conserved and accounted for.

What causes the spinning is the “mystery” of the MOVA globe.

Newton’s Cradle uses principles that have been known for centuries. My second favourite scientific toy is a newcomer. While still based on ancient knowledge, it incorporates technology that didn’t exist when Newton’s Cradles first appeared in the late 1960s.

The MOVA globe is a small plastic model of the Earth approximately 40 centimetres in circumference. A close look reveals there are two globes – an outer sphere of clear plastic and an inner sphere with the printed map of the Earth on it. A thin layer of clear liquid separates the two spheres. If the MOVA globe is placed on a level surface and allowed to sit quietly for a few seconds, the inner globe will begin to rotate slowly. What causes the spinning is the “mystery” of the MOVA globe.

See if you can work it out. I’ll give you some hints:

1  – A “mechanism” is hidden within the toy – the spinning is not the result of vibrations or residual energy left over from handling the globe.

2  – The mechanism operates smoothly and will run continuously for years as long as it has a decent light source – sunlight is best, but an incandescent light bulb will work.

3  – Other than the spinning printed globe, it has no moving parts.

When I first saw a MOVA globe almost 10 years ago, I had no idea what made it spin. Puzzle collector and expert Jerry Slocum explained the secret to me. As you may have surmised from hint number two, the globe is solar powered. Light enters through the printed material of the inner globe and powers some hidden circuitry. Also concealed within the inner globe are two or more bars that cross at the centre and are attached to the inner surface of the printed sphere, like spokes of a wagon wheel attached at points around the globe’s equator.

When a set of these bars or “spokes” is energised, they generate a magnetic field. This magnetic field then tries to align with the Earth’s magnetic field. In essence, the toy has become a compass. It spins in an effort to “point” north. After a few seconds, the inner circuitry shuts off the first set of energised spokes and energises a different pair. This new set of magnetised spokes then tries to point north and the globe spins a bit more. This constant switching from one set of spokes to another is what keeps the internal “compass” spinning.

A careful reading of the MOVA globe patent reveals the inner globe is floating in two different liquids. Both are clear but they have different densities – the heavier fluid sinks to the bottom and the lighter fluid rises. The inner globe is dense enough to stay in between these two fluids and doesn’t sink to the bottom of the outer clear plastic sphere or float to the top – either might cause friction that would interfere with the spinning globe.

Newton’s Cradle may win the prize for simplicity, but the MOVA globe is the champ when it comes to ingenious engineering.

The MOVA Globe in action.

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