Consider the example of the coin rolling around a coin of the same size. Intuitively we think …’OK. Same circumference, so the coin will rotate once as it rolls around a same-size coin. But this doesn’t happen. It rotates twice.
TWICE!
This observation is SOOOOOOOO counterintuitive we have to know why?…
Why?
The answer is interesting. The relevant point in the ROLLING COIN PARADOX is the centre of the rolling coin. The rolling coin rotates about that point. And that centre (the red dot in the gif below) moves through a circle twice the circumference of the stationary coin. It is much easier to understand when you see it. (Below)
Air resistance is a significant factor used by ski jumpers to increase their jump distance.
Ski jumpers crouch going down the ramp to reduce their X-section area and therefore their air resistence. Once they leave the ramp, ski jumpers try to increase their X-section area to increase their air resistence like Ski Divers to slow their vertical fall. But they have to land safely, so they keep their skis at a minimum angle.
Austrian Stefan Kraft in the Men’s Olympic Ski Jump at Milano Cortina 2026
Abby Hughes, USA, practicing in a wind tunnel.
Abby Hughes, USA, in the air
Here are the X-section areas for Abby Hughes:
Mathspig calculated the X-section area by the old-fashioned method of counting squares and rounding off the final count. Mathspig sized the two pics of Abby Hughes so that her head was the same size in both pictures.
Here is the formula for Air Resistance of Drag:
D = ½CApv2
Where C is the drag coefficient or constant, which depends on the shape and spin of an object. It is found by testing the object in a wind tunnel.
With Valentine’s Day approaching Mathspig has reposted this warning.
Chocolate contains a chemical called Theobromine. This alkaloid ( other alkaloids include cocaine, nicotine, caffeine, and strychnine) can kill humans. More infoWired Magazine.
How much chocolate is too much?
Firstly, the darker the chocolate the more Theobromine it contains.
According toAbout Chemistrybased on the highest possible toxicity:
* Vetmedicine: Cooking chocolate contains 8-10 times the Theobromine in Milk Chocolate.
According toWiredlarge doses of theobromine may cause “nausea and anorexia ….. sweating, trembling and severe headache.”
The Royal Society of Chemistrynotes that chocolate does not contain caffeine, but theobromine induces similar symptoms.
LD50 for the lethal dose for 50% of the population for Theobromine is:
Mathspig Blog 
