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How do I calculate the exit vectors of colliding projectiles?

The asker posted a question to which I responded with an explanation, an illustration, and a proof of concept. The asker expressed doubts about the answer despite proof. The answer was later down-voted by someone else, with the askers doubtful comment getting an up-vote. This is a question regarding physics and illustration clearly proves my answer as being correct.

The asker revealed further requirements after a discussion, so I posted a new answer taking the new requirements into account. I left my original answer as it correctly addresses the original question.

Another commenter believes the answer is an "over simplification", however almost all physics equations are simplified in programming, or rather, calculated with only as much accuracy as required. I could have included a fully physically correct answer, but my answer addressed exactly what the asker wanted.

I'm fairly new to Stack Overflow so I don't know if this sort of behaviour is tolerated, or accepted, or maybe even encouraged? As a contributor its very demotivating to spend time answering questions only to have the effort go unrecognised, or marked as "wrong" simply because an ignorant person doesn't "believe" the answer. Is this something that can be expected to happen often?

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There is no such thing as "unnecessary downvoting". People can downvote for whatever reasons they choose, whether you think they're wrong or not. There's nothing anyone can do about it, and that's completely by design. If you think another answer is good, upvote it. If you think your own answer is good, well, obviously you do, that's why you posted it. –  Cody Gray Aug 13 '11 at 11:50
    
I don't like this question. I downvoted it. –  Won't Aug 15 '11 at 12:23

3 Answers 3

up vote 5 down vote accepted

Let me preface this by saying that I'm not active on Gamedev, so I don't know anything about its unique culture or norms. What I can say is that people are entitled to express their opinion through votes, and comment votes, etc. Is that other poster's argument true? I have only the faintest idea, but he believes it is, and that's what he is expressing. It looks to me like someone gave you an upvote which far offsets the downvote anyway (+10 vs. -2).

It looks like you spent a lot of time on the answers, which is excellent. For various reasons, you may not always be rewarded for your effort on every question. It's not something to take to heart, just find another question you like and give an excellent answer!

I will say that if you have reason to believe that a user is going beyond criticism to become rude or abusive (which I don't think is the case here), flag your post for a moderator, and let them intervene instead of taking on the person yourself.

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1  
Thanks jonsca! That certainly puts it into perspective. –  Luke Van In Aug 13 '11 at 11:40

I'm fairly new to Stack Overflow so I don't know if this sort of behaviour is tolerated, or accepted, or maybe even encouraged?

There are a certain number of downvotes good, complete, correct answers will get. I like to call this "downvote noise."

It's unpredictable, and fighting against it usually it's worth it - as long as you continue to contribute, and respond to constructive criticism in comments, you will always find that you get more upvotes on average than downvotes.

This is true with any system where there's a human component to evaluation - sometimes some things just attract the wrong response from a random user.

Re-evaluate your answer, re-read the question to make sure you interpreted it correctly, and just move on.

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In this case, the asker was right. Your formula is incorrect, except in some very limited cases. (Those shown in your "proof"). It fails when the masses are different or when the projectiles don't hit each other directly. The downvotes are therefore justified in my opinion.

But don't take this personally. I think the quality of your post was very good. We all get things wrong some times. The best thing to do is learn from your mistake and move on.

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Those limited cases are what the asker specifically mentioned, and the answer is perfectly valid for a simple particle system where each particle is treated as a point. No other requirements were stated in the question. This kind of down voting causes more harm than good, as people reading the answer will automatically assume it's "wrong" and go and implement an over-complicated solution when the simple solution works perfectly well for simple requirements. Game development is specifically about using the simplest solution which works. –  Luke Van In Aug 13 '11 at 12:05
    
@lukevanin: The question states: "All projectiles are spherical". I agree about simplifying where possible, but in this case your formula fails to meet the requirements. –  hammar Aug 13 '11 at 16:10

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