Everyday Einstein Answers Your Emails
What’s conservation got to do with momentum? Do humans really have blue blood? Everyday Einstein answers some listener emails.
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Everyday Einstein Answers Your Emails
As a follow-up to last week’s podcast, in which I answered some comments submitted via iTunes, today I’m going to take on some of the emails sent to the Everyday Einstein address.
Conserving Conservation
Robert writes in to ask: “Could you explain what the ‘conservation’ in the conservation of angular momentum and the conservation of energy means? I seem to think it’s about saving or preserving something.”
Great question, Robert. The “conservation” part of “conservation of momentum” or “conservation of energy” means that after a certain event occurs, you end up with the same amount you started with.Â
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For example, let’s say you decide to take your date ice skating. While moving around on the ice, your date’s momentum is defined as her mass multiplied by her velocity. Likewise, your momentum is your mass multiplied by your velocity. If by some poor stroke of luck, you crash into her, both of your velocities will change (as might the nature of your relationship.)
However, if you recalculate the sum of your momentum and your date’s momentum after the crash, and compare it to the sum of your momentums before the crash, the conservation of momentum says that the total combined momentum of you and your date will not have changed. In other words, if you are really heavy and moving quickly, and crash into her, she will likely start moving much more quickly after the crash. The momentum is, therefore, conserved.
Of course, in real life you have to take into account things like friction, which can make the calculations more difficult.
Conservation of energy works the same way, by stating that energy is never really lost, just changed. So if you put energy into your car in the form of fuel, when that fuel is burned, the energy isn’t lost–it is converted into potential energy (the movement of the car), heat, and sound. If you could somehow quantify all of that energy and add it up, you would find that the total is the same as how much energy you started with. The energy is conserved.
Blue Blooded
Like many other myths of science, this one is particularly difficult to debunk because it is repeated so often.
Robin asks in exasperation: “I went to high school in southwest Georgia (I now live in Florida), and I was taught in biology class that blood in the veins is blue, and that it doesn’t turn red until it hits oxygen. We used to argue with the teacher that it’s red when a nurse is taking blood, and our teacher would say that’s because there was a little bit of oxygen in the vial. She would also say that the reason bruises are blue is because the blood beneath them is blue. Please debunk this myth.”
Like many other myths of science, this one is particularly difficult to debunk because it is repeated so often. As with the myth of how airplanes fly, I’ve even seem some otherwise reputable science websites repeating this myth.Â
However, rest assured that no human has blue blood. It doesn’t matter how much or how little oxygen your blood contains, it is always red. (Though the exact shade of red does differ based on oxygen content.) The reason blood is red is because of hemoglobin, which contains iron, giving it a red color.Â
The reason veins looks blue isn’t because they are that color, but because the way light travels through your skin makes them look blue. (In fact they don’t really even look blue; experiments have shown that the wavelength they give off is more of a reddish brown, but human brains for some reason perceive them as blue.)
If you were, for example, to stick your finger in a cup of vegetable oil and prick it with a needle (which I don’t necessarily advise), you would see your blood emerging as a red fluid, despite the fact that it is not in contact with any oxygen.Â
Nick Anthis over on Science Blogs has a great article explaining more technical details on why veins look blue, even though they aren’t.Â
But note that there are some animals and insects that do have blue blood, and blood in other colors, too. Spiders have blue blood for example, thanks to the relatively large amount of copper it contains.
So yes, Robin, you can rest assured that even the most blue-blooded of teachers actually have red blood.
Conclusion
That’s all of the Q&A we have time for today. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.comcreate new email
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