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How a Differential Gear Works

Ever wondered how a differential gear on a car works? Well, if you're like me, your first question is just what the heck is a differential? Wikipedia says (emphasis added):

A vehicle's wheels rotate at different speeds, mainly when turning corners. The differential is designed to drive a pair of wheels with equal force, whilst allowing them to rotate at different speeds. In vehicles without a differential, such as karts, both driving wheels are forced to rotate at the same speed, usually on a common axle driven by a simple chain-drive mechanism. When cornering, the inner wheel needs to travel a shorter distance than the outer wheel, so with no differential, the result is the inner wheel spinning and/or the outer wheel dragging, and this results in difficult and unpredictable handling, damage to tires and roads, and strain on (or possible failure of) the entire drivetrain.

This video explains the whole thing (note: the first two minutes or so are a demonstration of synchronized motorcycle riding, which you may or may not find exciting). It's kitschy, but also educational -- through a step-by-step engineering demonstration, this vintage video makes it clear how all this technical car stuff works. Chevrolet Motor Division (General Motors Sales Corporation) Presents: AROUND THE CORNER...

See also: Richard Feynman Explains Trains, in which he explains a similar issue faced by trains turning corners on train tracks.

(Via Kottke.org.)

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Belly Flop Physics 101: The Science Behind the Sting
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Belly flops are the least-dignified—yet most painful—way of making a serious splash at the pool. Rarely do they result in serious physical injury, but if you’re wondering why an elegant swan dive feels better for your body than falling stomach-first into the water, you can learn the laws of physics that turn your soft torso a tender pink by watching the SciShow’s video below.

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What's the Saltiest Water in the World?
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Saltwater is common around the world—indeed, salty oceans cover more than two-thirds of the globe. Typical saltwater found in our oceans is about 3.5% salt by weight. But in some areas, we find naturally occurring saltwater that's far saltier. The saltiest water yet discovered is more than 12 times saltier than typical seawater.

Gaet’ale is a pond in Ethiopia which currently holds the record as the most saline water body on Earth. The water in that pond is 43.3% dissolved solids by weight—most of that being salt. This kind of water is called hypersaline for its extreme salt concentration.

In the video below, Professor Martyn Poliakoff explains this natural phenomenon—why it's so salty, how the temperature of the pond affects its salinity, and even why this particular saltwater has a yellow tint. Enjoy:

For the paper Poliakoff describes, check out this abstract.

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