The Senses

Everyone knows the classic five senses: sight, hearing, touch, taste, and smell. But do we not sense more than that? In fact there are quite a few additional senses we could include. Here are a few:

Temperature - We sense temperature, but it's worth noting that we don't sense the temperature of other things, only the temperature of our own bodies. This is why steel will feel colder than paper even if they are the same temperature. The steel is much more effective at cooling our skin, and our skin temperature is what we actually sense.

Motion - More precisely acceleration. Each ear contains two accelerometers. One measures vertical acceleration and the other, horizontal. They work by feeling with a hair when a weighted membrane is stretched by inertial forces. Note that we cannot detect velocity. Cruising at high speed in a car doesn't really feel different from standing still if the ride is smooth enough. For that matter nor does speeding through space on a planet.

Body Position, Proprioception - If you block your other senses and have someone change the position of your arm, you will be able to at least somewhat detect the change and report the new position. This awareness is achieved thorough sensors in your muscles and joints that report when and how much they are being stretched.

Spinning Things

Conservation of momentum (previously discussed) can be extended to spinning things. When something spins in place, the object as a whole is not going anywhere, but the individual bits (each with some small mass) are moving at different speeds around the axis, with bits going faster the farther they are from the center. Conservation of momentum applies to each of those bits, so it also applies to them all together. When we talk about this summation of momentum in a spinning situation we call it angular momentum and give it the symbol, L.

So L = I x Ω, where I is a measure of the thing’s shape. If there’s a lot of the thing far from the spinning axis, I is big. Ω is how fast it’s spinning, like ten turns per second.

The cool thing here is that L is constant, so if the shape of the spinning thing changes and I increases or decreases, Ω has to change in the opposite direction.

This is very useful. Think about an ice skater going into a spin. At the start, they have arms way out, one leg trailing way back (big I), and are turning very slowly (small Ω). When they pull their arms and legs tightly in to the center, I gets much smaller, so Ω has to get much bigger - they spin fast!

Let’s see it an action:
Figure skater
Cats falling 
At the playground 
And this guy at taco bell 

Decimate

Decimate is one of the most egregiously misused words today. The difference between intended and actual meaning is almost as great as with literally/figuratively, the true meaning is right there in the word, and the historical use is pretty amazing and not to be forgotten.

Modern usage is typically that to decimate means to drastically reduce, similar to annihilate. In the historical usage decimate meant to reduce by 1/10th, actually a fairly small reduction.   
Language is a fluid and evolving thing, and words may change meaning over time, but this example seems unfortunate. 

Note that "decim" in decimate? As with decimal, or decibel, it comes from the Latin word decimus, meaning 1/10th. Note decibel actually means 1/10th of a Bel, the actual unit of sound intensity, named for Alexander Graham Bell. Since the original meaning can be guessed just from it’s spelling, it’s a bit confounding that it has managed to drift so drastically. Note that annihilate is more true to it’s construction, with that Latin "nil" inside meaning “nothing.”

The final reason the misuse is a shame is that the original use is a remarkable and more unique idea. About 25 centuries ago, the Roman army came up with a clever and horrible punishment for mass desertion. Typically, desertion would be punished by death, but they did not want to lose their own soldiers en mass. And, these being fighting men, such a punishment may be difficult to enact on a large group. The solution was to randomly sentence one in ten of the offenders to death. The whole mass would feel the real fear of punishment, all would feel the loss of people they knew personally and take it to heart, and those spared could be counted on to not rebel, and even to help enact the sentence under orders. 

That punishment has been applied as late as the first world war. The word was also used to refer to the tithe (typically 1/10th of one’s income) staring probably in the 1600’s, and the latest use as referring to a massive reduction seems to have arisen in just the last 100 years or so.