Trying to understand Newton/seconds, Impulse

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It's like "The Force".

"There is no try, only do".

Being able to judge things like balance and weight by handling items helps a whole bunch too.
 
The graphs make sense, the numbers on the motors don't.. (If they add the N equivalent to the graphs, that might help correlate the two..) All Aerotech motors come with a thrust curve graph..

Or add a label to the right side of the graph in Newtons...
 
Blackbrandt is absolutely right. All I'm saying is mass and weight are too easily confused when talking about pounds. When's the last time anyone reported reported the mass of his/her rocket in slugs?

In retrospect, maybe the best lesson from this thread is "Don't trust anyone from Maryland." (Though maybe I'll meet some of you MDRA guys next year at LDRS.)

We once had an argument at the office lasting approximately two hours over whether to convert metric tons to pounds force or pounds mass. :)

The secret to calculus is that it's all about areas and slopes. Sure, we dress it up with fancy words like integral and derivative, but that's just code. An integral is the area under a curve. A derivative is the slope of the curve. So if you have two thrust curves, you can tell pretty much at a glance which one has the most area under the curve and will likely send your rocket further. That's not 100% true, since a super short burn (eg F120) will get your rocket going really fast leading to higher drag and a lower flight, but it's close enough.

Unit conversions are always messy. I used to think my co-worker was overdoing it when he laid out every conversion in a line and then crossed out units above and below until he had the units he was looking for. Then I realized he got them right every time. :)
 
We once had an argument at the office lasting approximately two hours over whether to convert metric tons to pounds force or pounds mass. :)

The secret to calculus is that it's all about areas and slopes. Sure, we dress it up with fancy words like integral and derivative, but that's just code. An integral is the area under a curve. A derivative is the slope of the curve. So if you have two thrust curves, you can tell pretty much at a glance which one has the most area under the curve and will likely send your rocket further. That's not 100% true, since a super short burn (eg F120) will get your rocket going really fast leading to higher drag and a lower flight, but it's close enough.

Unit conversions are always messy. I used to think my co-worker was overdoing it when he laid out every conversion in a line and then crossed out units above and below until he had the units he was looking for. Then I realized he got them right every time. :)
That's exactly how i do every single one of my conversions. Easiest way to make sure that you're never going to miss a single piece. :p
 
Unit conversions are always messy. I used to think my co-worker was overdoing it when he laid out every conversion in a line and then crossed out units above and below until he had the units he was looking for. Then I realized he got them right every time. :)

I have done this for 30 years as an engineer. It's the only way to assure yourself you did it correctly.

You quickly learn in your first engineering class that English units suck! SI units are the only way to go. Even my employer (who you may think of as being old school) changed to SI units 35 years ago. It is the global language of science and engineering.
 
https://en.wikipedia.org/wiki/Metrication

So, only three countries seem to use the Imperial system, the US being the biggest user.. All others have converted, or in the process of.. (It's an interesting read!)

In Canada, we're ambidextrous because we deal with the US on every level, daily! So we can (mostly!) convert Km to miles, Gallons to Liters, pounds to Kg, etc.. The various jobs I've had (mech design) have been either metric or imperial measurements (mostly Imperial, due to the US market; selling to, and parts / supplies from).

Although I must admit, I do find it funny that the US is a hold-out for a system not readily used outside N. America..
 
https://en.wikipedia.org/wiki/Metrication

So, only three countries seem to use the Imperial system, the US being the biggest user.. All others have converted, or in the process of.. (It's an interesting read!)

In Canada, we're ambidextrous because we deal with the US on every level, daily! So we can (mostly!) convert Km to miles, Gallons to Liters, pounds to Kg, etc.. The various jobs I've had (mech design) have been either metric or imperial measurements (mostly Imperial, due to the US market; selling to, and parts / supplies from).

Although I must admit, I do find it funny that the US is a hold-out for a system not readily used outside N. America..

Our form of government doesn't allow changes to be forced as in some countries, and schools here teach the metric system but dont use it, nor does the construction industry, transportation industry or a host of other industries here. Until the schools and businesses change metric will not be a standard in the US.
 
Our form of government doesn't allow changes to be forced as in some countries, and schools here teach the metric system but dont use it, nor does the construction industry, transportation industry or a host of other industries here. Until the schools and businesses change metric will not be a standard in the US.

They started teaching metric in the 1970s, with a goal toward conversion. I think they figured that by educating the young 'uns, they could wait till the older generations (who wanted nothing to do with the metric system) died off, and then convert when the kids were grown up. But for unknown reasons, it never happened. Perhaps the infrastructure costs of such a conversion were more astronomical than expected.

Since the 1970s, I have heard no talk of conversion. I guess now they figure that as long as kids are taught it in school, they can make use of it if they want to, and they won't be lost when visiting other countries.

Although, on that last point, I have to say that it didn't work for me. :wink: When I went to Canada, I was wondering what the speed limits would be like. I was so psyched on the other side of the border when I saw that the speed limit was 100! Then I realized it was 100 kph, which was actually slower than the 65 mph I had been driving to get there. :facepalm:

Same thing happened the first time I bought gas. This was back when the price of gas was about $1.25/gal in the USA. I looked at the gas pump and got so excited when I saw the price was $0.35! But then I realized that that was per liter, which made it about $1.40 for a little more than a gallon. Bummer. But then I also realized that that was in Canadian dollars. So the price of gas was a little cheaper after all.

I think about my parents, though, and there is no way they could handle conversion. If I said to my mom, "Please pour me a liter of water," she would not have a clue how much that is. Or if I said, "How many grams of lunch meat do you want me to get?" she would say, "I don't know; how many grams are in a half-pound?"
 
I did some work for a company, and they were using 'metric' prefixes for their imperial measurement accuracies. if was funny to hear them say 'Deci / centi-pounds' for 1/10th or 1/100th of a pound..
 
I was in primary school when the changoever from imperial to metric happened here in Australia. I handle conversions very well. Doing physics or engineering in anything other than SI units I am sure would mess with my mind in not a good way!

Ever gone into a shop and asked for a six inch metric ruler? :)
 
One thing I wanted to mention: The larger the number after the letter does not (always) equate to a higher attitude. Some think the bigger the number (after the letter) the higher it'll go..

Do a simulation, look at the numbers. A longer push at a lower thrust can get higher than a shorter initial push at a higher thrust..

(I recently mentioned I got a pretty good launch on a G64. I got a suggestion to try a G80. I will try, but my sims show I'll loose about 200'..)
 
One thing I wanted to mention: The larger the number after the letter does not (always) equate to a higher attitude. Some think the bigger the number (after the letter) the higher it'll go..

Do a simulation, look at the numbers. A longer push at a lower thrust can get higher than a shorter initial push at a higher thrust..

(I recently mentioned I got a pretty good launch on a G64. I got a suggestion to try a G80. I will try, but my sims show I'll loose about 200'..)

The perfect example of that is a VMax motor. They are awesome, but they don't come close to setting altitude records.
 
Otherwise we would never get our rockets back. :grin:

We'd be okay thanks to gravity.

That reminds me that one of the first programs I ever wrote was, of course, a rocket flight simulator. I don't recall if I used the code in the Handbook of Model Rocketry as a basis for it or not. But, I do remember playing with things like changing the effects of gravity and drag to simulate launching a rocket from the surface of the moon or Mars.

-- Roger
 
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As I phrased in in a thread a year or so back.... the rocket was fine until it hit the ground. :p
 
Great thread.... I prefer to measure speed in 'furlongs per fortnight'....
 
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