Month: April 2017

I recently asked on Facebook and Twitter for everyone, adults and kids, to send me their science questions. My plan is to collect them as they come in and do a post now and then answering the questions. Don’t wait, send in yours!

My first questions come from Dave Y. and his son, Jack. Dave wrote: “What is the purpose of retractable claws (cats) vs permanent claws (canines, bears, etc)?”

At first I thought that there might be a physiological difference, but that they serve a similar purpose, like antlers vs. horns. Perhaps they got to a similar place from different starting points through convergent evolution, but cats, dogs, and bears aren’t that far apart on the evolutionary tree. Also, while I know a ton about cat claws from 20 years of trimming them, I don’t really know much about bear claws (aside from the pastry).

I discovered that bear, cat, and dog claws are all pretty much the same. The main difference is that cat claws are protractile, which means the claws are normally sheathed, but the animal can flex and make them extend (as opposed to normally being out, or always being out). Protractible claws are found on several predatory animals, but mostly cats.

I couldn’t find a clear answer about why cats have protractible claws, but the most likely reason seems to be that it helps them avoid becoming stuck when climbing trees and allows them to let go of their prey once they’ve killed it. When Harry, my orange tabby, got older, he stopped using his scratching post. Without scratching, his claws got long and sharp. He would sometimes get stuck on the carpet or blankets because the claws would stick out beyond the sheath, which supports the idea. Also, it meant that it was time for a claw trimming (which he hated).

Bottom line: if a cat scratches you, just remember, he had to go to extra effort to pull those claws out. If he merely bats you with claws in, he’s probably just playing. Probably.

Jack’s question was: “How does Iron Man’s cannon shoot?” I’m not as up on my Iron Manology as I should be, so I had to look up his cannons. I assume Jack is talking about the blasts Iron Man shoots out of his hands. It turns out they are “repulsor beams” that are powered by the tiny “Arc Reactor” in his chest. In the Marvel universe, repulsor technology was originally designed as a missile propulsion system, and Tony Stark adapted it to work in the Iron Man suit. The repulsors in his boots allow him to fly.

Repulsors aren’t real, but they behave similar to rocket engines. The difference is that rocket engines need to burn fuel to generate thrust while repulsors appear to convert energy from the reactor directly into thrust. In that way, repulsors are similar to ion engines, which generate thrust using electricity to accelerate ions (charged atoms) and shoot them out of the back of the engine. However, current ion engines can’t produce nearly that amount of thrust. In this case we are squarely in the science fiction world, but grounded in reality.

If you want to keep up to date on the shifting boarder between science fiction and reality, keep your eye on the quantum vacuum plasma thruster, a.k.a. “EmDrive” or “microwave thruster”. According to a NASA study,  it can, apparently, generate thrust without any propellant (fuel), which is ideal for a space ship where weight is a big concern. Again though, the thrust they measured was very small compared to the amount needed to let a person in a metal suit fly.

Bottom line: Iron Man has tiny rocket engine-like devices in his boots and gloves. He can turn them on to fly, or shoot short bursts at his enemies. Imagine getting a second’s worth of rocket engine aimed at you. Not a good idea to get on Iron Man’s bad side!