Where Grey Matter meets Dark Matter

Cosmic Tidbits

Gauss' addition trick
Momentum of baseball bats

26 January 10, 3:45 pm


There are some really cool critters in the ocean. Seahorses might be the coolest. Averaging about 15cm tall, they are a carnivorous fish and also monogomous.

They have a number of quirks, one being that the male is the bearer of the young. But a less-known fact is that they have no stomach. They suck in plankton with their snout and it passes straight through their digestive system. This means that they can't store the food and get energy out of it slowly over time, so they need to eat constantly.

You may know people like this, but I'll bet they're not as cute as seahorses are.

Source: National Geographic

7 April 09, 3:47 pm

Gauss' addition trick

Legend has a lot of things - and this is one of them: Karl Friedrich Gauss, the greatest of mathematicians, astounded his primary school teacher by correctly adding up the numbers between 1 and 100 in seconds - the answer is 5050. The story goes that precocious little Karl was difficult to teach since he was far ahead of the other kids in his class, and so the teacher gave Karl something to do that should keep him busy for a while. It didn't.

The trick is to notice that 1+100=101, 2+99=101, 3+98=101... So each pair gives 101, and there should be exactly 50 pairs. So 50*101=5050.

In general, you can do the same thing for any even number N using the formula:


There is also an equivalent formula for odd. Feel free to figure it out.

12 March 09, 4:52 pm

Momentum of baseball bats

Imagine two baseball bats, one suspended by a string, the other held rigid in a vice. An identical baseball is fired at each, aimed at the same part of the bat.

The balls will rebound at the same speed. This is because the collision time is smaller than the time it takes for pressure waves to run up and down the bat, so the subsequent movement of the free bat isn't noticed by the ball.

There are exceptions, of course. For more information, see:
Dynamics of the baseball-bat collision
Everything you wanted to know about the science of the bat-ball collision

Thanks to David Barry for this tidbit.

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