So suppose you saw something that looked like this:
This is a ball shot out of a shooter device. Well, it is a vypthon animation of a ball. What would you do if you came to see this video? If I had not made it, I would say it is an unrealistic video. It does not agree with my basic model of how things move after being thrown or shot or whatever. Interestingly (but unrelated) there was a set of physics questions that showed different possible paths of a thrown ball. The path representing the motion above was a common choice.
Like I said, I made that animation. Here is another one. In this second animation, there are two balls. The red ball is exactly the same motion as before. But, in this case there is also a blue ball that is shot with the same initial velocity but accelerates as a normal projectile motion object would.
So, if I see something like the motion of the red ball, here are the possible things that could be going on:
- It is wrong. Either the simulation is wrong or the observation is wrong. Really, this isn’t too uncommon. If I drop two balls of different masses in front of a class from the same height at the same time, quite a few students will say they saw the more massive ball hit the ground first.
- The basic physics is wrong. For this case, the basic physics says that a ball shot from a launcher will have a constant acceleration in the downward direction. This acceleration would make the ball move in a parabolic path. If there is air resistance, the path would not be parabolic but it would also not move in a straight line like that. This is a tough option. If we say the basic physics is wrong, then we have to go look at all the other cases where this worked.
- There is something else going on here. For this case, maybe there are some other forces that are not obvious. With these non-obvious forces (like maybe an electric force or something) the basic physics ideas are still valid.
Now, what about another case? Here we come back to this “Directly Down Wind Faster Than the Wind” business. I originally posted about this quite some time ago (like 3 servers ago). This stuff is the same as the red ball above. To a physicist, it looks like energy would not be conserved. Oh, stop right there. I know what you are going to say because I have heard it before: but you get energy from the wind. I still don’t get it.
Does this kind of machine violate the conservation of energy? Does this machine show that energy is not conserved? Or, maybe something different is going on here. Hopefully you can see why some physicists would say “errr?”
Ok – so I keep getting emails and comments saying this down wind faster than the wind machine works. That would make my claim from earlier that it did not work wrong. So, which of the above options would this situation fall into? I would say that there must be something else going on here. Abandoning conservation of energy would be dangerous (because it works so well).
Note: I will not be discussing the physics of this machine. Why? Is it not interesting? No, there is some interesting stuff going on here. I will not discuss the physics because it doesn’t really match with my agenda for this blog. My main goal is to look at cool stuff and use it to try to explain some physics. I tried that before with this machine and failed. If I were to try again, I do not think it would be too productive. Let me just say that the down wind machine builders are some pretty pumped up people. Being pumped up is a good thing. I am pumped up about VPython. But when they are way more pumped up than I am, some feelings get hurt.
Two more quick comments. Why is there no wikipedia article for down wind faster than the wind? Why are there down winders so anxious for me to say it works? If it works, does it matter what I say?
Comments: This is the kind of post that has the ability to generate pumped uped comments. To be a good comment hoster, I am going to start with the likely comments. If you want to write one of these comments, you can simply type the number corresponding to the comment you would like to make. You know, to save time.
- I, for one, welcome our new down wind faster than the wind powered cars.
- You are in idiot. You don’t understand physics. You should be fired.
- Why can’t we attack you like you attack Sport Science?
- Reply: good point. Maybe I should stop attacking Sport Science. Help me, I can’t stop.
- I see what you are up to. You didn’t ACTUALLY say you were wrong. You are looking for some logical loop hole so you won’t have to actually say you were wrong. Why can’t you just be a man and say you were wrong.
- You say you don’t understand down wind faster than the wind machines. It is relatively simple. You see, there is this wind and you get energy from the wind. How hard is that? Sail boats go faster than the wind.
- I, for one, do not believe in down wind faster than the wind. Will you please look over my calculations that show this can not work?
- I am a true believer. Please support my plans to convert all car and air planes over to down wind faster than the wind machines. It will lead to world peace just like cold fusion.
- When Zerg returns, it will be in a directly down wind power vehicle.
- I have these plans for a machine that will make energy. I want to submit it to a physics journal, but no one will accept it because I am not in an academic position. Would you be the co-author and submit it for me?