The accidental scientist

  Running in the rain Sometimes I watch people running because it rains, and I wonder why they do it. Simple: if you halve the time you spend in the rain, you must halve the volume of water collected right? Wrong. Things are not that simple. Today I decided to look how wet does a person gets when walking or running 100 metres under the rain. How much rain? Let ’ s say 100mm in the rain gauge for a day. This gives an average of 1.16 millilitres per square meter per second. How long does it take? About 71 seconds if you walk, 20 seconds if you run. Usain Bolt can do it in 10 seconds. I gathered all this in a table. Here is a simplified version of it: Speed Time to do 100m Volume of water collected on top of head and shoulders (about 0.1 sqm) Volume of water collected on face and front of body (about 0.85 sqm) Total collected Walking 71 sec. 8.29 ml 10.96 ml 19.24 ml

    Last week we talked about Pythagoras who discovered that the Earth is round about 500 BC. Well, about 300 years later, another smart guy called Eratosthenes decided to calculate the circumference of the Earth. No computer, no GPS, no map. How did he do that? Eratosthenes is the founder of geography. He lived in Alexandria, Egypt and was among other thing the conservator of the Alexandria library. His method is based on two observations: 1-       There was a place called Syene in the South of Egypt. Nowadays we call it Aswan. At Syene, on June 21 st and at noon, the sun rays reach the bottom of a vertical well. 2-       At the same time at Alexandria, on the North coast of Egypt, the shade of a gnomon (a vertical post stuck in the ground) forms an angle of 1/50 of a circle with the post. Looking at the picture we can see that the earth being round, its circumference is 50 times the distance between Syene and Alexandria. So this had to be measured with some accuracy. This in

Around 500 BC Pythagoras and his Greek mates noticed that during a Moon eclipse, the shadow of the Earth on the Moon was always round. If the Earth was a disk, its shadow would look like an oval most of the time. The only shape whose shadow is always round, no matter where the light comes from, is a sphere. They concluded that the Earth shape was a sphere. Smart! The earth roundness limits how far I can see from the seaside. Walking along the beach near Byron I wondered about that. My eyes are 1.7m from the ground, I call this height h. If R is the Earth radius, the distance between them and the Earth centre is R+h. If I call d the distance to the horizon, I can apply Pythagoras rule to the triangle formed by my eyes, the Earth centre and a point anywhere on the horizon: R 2 + d 2 = (R+h) 2 The Earth radius R is about 6371km. I spare you the maths. With d and h expressed in metres, the solution is: d = 3569 x (square root of h) So if my eyes are at h=1.7 m from the ground,

  In the night between 11 and 12 October 1492, Christopher Columbus luckily ended up in the Bahamas. To his credit, he is the first navigator who followed the Trade Winds across the Atlantic Ocean. Honestly, sailing across the Atlantic in that direction is relatively easy. I bet coming back would have been a lot harder because he had to go a lot further North to find some decent Westerlies (and storms … ) and come back home via the Acores. Why are the winds like that? The Equator is hot so the air rises there, which creates a depression. The hot air goes North (and South) all the way to about 30 degrees of latitude, then comes down and goes back to the Equator. If the Earth was not spinning, the prevailing winds in the intertropical zone would be Northerlies in the North and Southerlies in the South. Simple. But the Earth spins, so the winds are deflected to the right in the Northern hemisphere, and to the left down South. This is called the Coriolis Force. It explains the Trade