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# geometric similarity

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1. in this question , Lm / Lp = 1/ 6 ? or Lp / Lm = 1/6 ? Lp = length of prototype , Lm = Length of model

i really have no idea... can someone help please?
2. (Original post by wilson dang)
in this question , Lm / Lp = 1/ 6 ? or Lp / Lm = 1/6 ? Lp = length of prototype , Lm = Length of model

i really have no idea... can someone help please?
Lm/Lp = 1/6
3. (Original post by natninja)
Lm/Lp = 1/6
can you explain why are you so sure that Lm/Lp = 1/6 ????
4. (Original post by wilson dang)
can you explain why are you so sure that Lm/Lp = 1/6 ????
because the model is obviously going to be smaller
5. (Original post by natninja)
because the model is obviously going to be smaller
Do you mean the model can be only smaller, and can't be larger than prototype??

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6. (Original post by wilson dang)
Do you mean the model can be only smaller, and can't be larger than prototype??

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Yes. The idea is to have a smaller model because it's cheaper, easier to make and fits in a smaller wind tunnel. There is no reason why the model would be larger - if you could build a larger model, you'd just build one the correct size.
7. (Original post by natninja)
Yes. The idea is to have a smaller model because it's cheaper, easier to make and fits in a smaller wind tunnel. There is no reason why the model would be larger - if you could build a larger model, you'd just build one the correct size.
I also encounter the same question which the ratio is in terms of a:b , where a is larger than b ,
Let's say a is 5, b is 1 , does it also mean Lp/Lm is 5???? Since you said that the model must be smaller than prototype?

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8. (Original post by natninja)
Yes. The idea is to have a smaller model because it's cheaper, easier to make and fits in a smaller wind tunnel. There is no reason why the model would be larger - if you could build a larger model, you'd just build one the correct size.
I also encounter the same question which the ratio is in terms of a:b , where a is larger than b ,Let's say a is 5, b is 1 , does it also mean Lp/Lm is 5???? Since you said that the model must be smaller than prototype?
9. (Original post by wilson dang)
I also encounter the same question which the ratio is in terms of a:b , where a is larger than b ,
Let's say a is 5, b is 1 , does it also mean Lp/Lm is 5???? Since you said that the model must be smaller than prototype?

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Can you think of a sensible reason for building a model bigger than the prototype?
10. (Original post by natninja)
Can you think of a sensible reason for building a model bigger than the prototype?
No, but, I saw the question like this, I doubt that is that similar to the previous case, which the model is smaller??

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11. (Original post by natninja)
Can you think of a sensible reason for building a model bigger than the prototype?
when the scale ration is 6: 1 , does it mean the Lm / Lp = 6 , which model is 6 times larger than P , or Lp/ Lm = 6 , which means prototype is 6 times bigger than model ????
12. (Original post by wilson dang)
when the scale ration is 6: 1 , does it mean the Lm / Lp = 6 , which model is 6 times larger than P , or Lp/ Lm = 6 , which means prototype is 6 times bigger than model ????
It requires you to apply a small amount of common sense. I don't see any reasonable reasons to make a model bigger than the thing so the model is clearly the smaller of the two.

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