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double post. Please ignore.

Flavorflav wrote:

quizbowl wrote:The top three run times were 2.07s, 2.25s and 2.37s at WLI regionals - the test was rather easy and didn't really affect the score. Basically, it was the fastest that won.

What was the mass of the sled?

250 grams

quizbowl wrote:

Flavorflav wrote:

quizbowl wrote:The top three run times were 2.07s, 2.25s and 2.37s at WLI regionals - the test was rather easy and didn't really affect the score. Basically, it was the fastest that won.

What was the mass of the sled?

250 grams

do you know those cars' masses?

personasaurus rex wrote:do you know those cars' masses?

My guess would be 201g... there's no point in making them any heavier than necessary, right?

quizbowl wrote:The top three run times were 2.07s, 2.25s and 2.37s at WLI regionals - the test was rather easy and didn't really affect the score. Basically, it was the fastest that won.

10th grade, no Physics yet - what should I study?

Propeller: got a good one by dissecting an old computer

Primate wrote:

personasaurus rex wrote:do you know those cars' masses?

My guess would be 201g... there's no point in making them any heavier than necessary, right?

yeah, but it's hard to get them down to minimum mass without sacrificing a little speed...

Tinkerer wrote:

quizbowl wrote:The top three run times were 2.07s, 2.25s and 2.37s at WLI regionals - the test was rather easy and didn't really affect the score. Basically, it was the fastest that won.

10th grade, no Physics yet - what should I study?

Propeller: got a good one by dissecting an old computer

Try learning some physics anyway; it was a huge component of our test. It's really not all that complicated; just learn the basic equations for relating magnetic fields to electricity. (Here's a great introduction, and SparkNotes to sum it up.)

Are you sure a computer fan is the best option? They're generally designed to circulate air, not for propulsion.

Primate wrote:

Tinkerer wrote:

quizbowl wrote:The top three run times were 2.07s, 2.25s and 2.37s at WLI regionals - the test was rather easy and didn't really affect the score. Basically, it was the fastest that won.

10th grade, no Physics yet - what should I study?

Propeller: got a good one by dissecting an old computer

Try learning some physics anyway; it was a huge component of our test. It's really not all that complicated; just learn the basic equations for relating magnetic fields to electricity. (Here's a great introduction, and SparkNotes to sum it up.)

Are you sure a computer fan is the best option? They're generally designed to circulate air, not for propulsion.

Newton's Third - move air out the back and the car will move forward. The real problem is that computer fans are designed to be quiet, which is likely to reduce their efficiency.

Flavorflav wrote:

Primate wrote:

Tinkerer wrote:10th grade, no Physics yet - what should I study?

Propeller: got a good one by dissecting an old computer

Try learning some physics anyway; it was a huge component of our test. It's really not all that complicated; just learn the basic equations for relating magnetic fields to electricity. (Here's a great introduction, and SparkNotes to sum it up.)

Are you sure a computer fan is the best option? They're generally designed to circulate air, not for propulsion.

Newton's Third - move air out the back and the car will move forward. The real problem is that computer fans are designed to be quiet, which is likely to reduce their efficiency.

Well, sure, but the shape can drastically effect efficiency as well. You want to minimize drag while maximizing thrust, optimizing pitch, etc, etc.

Of course, prop design isn't consequential until you get down to the three-four second range. The difference between a 45 second run and a 5 second run is all balance.

Primate wrote:Well, sure, but the shape can drastically effect efficiency as well. You want to minimize drag while maximizing thrust, optimizing pitch, etc, etc.

Of course, but a shape that is good for moving air is good for moving air, is what I am saying. It shouldn't really matter whether the assembly is on a fixed platform or not. The big problems are that fans are missing some design considerations (like weight) and have others (like quietness) that are likely to make them suboptimal. I have seen at least one really good maglev with a ducted fan, though.