Brand new at this please help !

[Jon]

Not many people are following this.

I are.  Wayno

Me to; I'm learning stuff.

FFS Taper I don't tortoise he was trying to find out wether you could tap a few calculator buttons but wether you could grasp the concept.
As far as your question how do you make equal changes in different things?,especially when in the equation in question they have different effects at different speeds.
A little bit of drag at low speed has FA effect but a little bit more hp helps a lot, at high speed a little bit of horsepower does little but a small reduction in drag is significant.

What is more effective 6 apples or 1/2 a dozen pigeons?

I do thank you for antagonizing some intelligent people enough to make for some interesting reading
jon

[taper41]

your simple aglebra shows that drag has more of an effect.

so how can both answers be correct with different outcomes. Help me out here tortoise
If your algabra equation isn't showing whether drag or power is a more significant factor to top speed then what is it showing ?

Remember earlier when I mentioned you had to be very careful about definitions?

The problem here is actually the word problem not the math. You asked what on the surface appeared to be a very simple question.
You basically asked "if you make equal changes to drag and power" is one more effective than the other?
The word problem that taper is holding to is actually a flawed statement with respect to your intent I believe.

A 25% reduction in drag is not equivalent to a 25% increase in power because of the way fractions and percentages work.

It suddenly dawned on me when I recalled tortises comment early in the thread regarding percentages of change and when I used a 50% change it was very obvious logically what was going on.

Lets go to the 50% change because it is a bit more intuitively obvious.

If you cut drag by 50% you are reducing drag to 1/2 of its original value. Increasing power 50% IS NOT an equivalent change, the equivalent change is doubling power. That becomes obvious  when you look at the fractions instead of as percentages. Drag reduction to 1/2 its original value if you invert that fraction it becomes 2/1 --------- that is the correct "equivalent" change in power, not a 50% increase.

1.5 x power is not the reciprocal of 0.5

If you use whole number fractions instead you can easily see that a 50% increase in power is really 3/2 of the original power, where the true reciprocal is 2/1 or 4/2.

Likewise the 25% reduction in drag is really 3/4 of the original so the reciprocal change to power is 4/3 = 1.33333 not 125%.

The word problem as stated does not actually do what you intended which was to determine what equivalent changes in power and drag rate with each other. It is a subtle problem with percentages that bites people all the time!

In very small percentage changes the error is so small it can be pretty much ignored, for example a 2% reduction in one thing vs a 2% increase in another.
The 2% reduction if reduced to a common fraction is 49/50, so its reciprocal is 50/49 which is 1.020408. The error being so small it gets lost in most cases. If however you make big changes however that error quickly grows.

Taper is correct if we stick to the word problem exactly as stated.
If how ever you restate the word problem to match what I believe was your intent, and how I saw your first query is "if you make equivalent changes to drag and power do they produce the same results?".

Restated that way and doing the proper math to find the reciprocal of the drag reduction they are exactly equal. BUT you will notice that your power increase as a percentage will always need to be larger than the equivalent reduction in drag.

In the real world land racing cars are always running at the limits of the technology and the reductions in drag that are possible within the rules and the increases in power available in the rules are usually small. Drag reduction gets very much harder as you drop the drag, where power is a bit more open to increase if your willing to change engine displacement, add a blower or switch to a fuel class etc.

This is why my first calculations where the terminal speed was held constant checked out exactly but when we changed the form of the calculation to vary drag and power by a percentage and see how the terminal speed changed we started to see the error.

Larry

I understand , adding increasing 200 by 50% which would obviously be 300 is not the equivalent change to decreasing .20 by 50% where as you are only adding half of 200 to make 300, you are cutting, .20 to actually make HALF of what it originally was. the equivalent would be increasing 200 to 400.

[taper41]

Basically decreasing something by 50% and increasing something by 50% is not the same thing, that goes for any percentage,and are not equivalent, I is this correct?

[tortoise]

Basically decreasing something by 50% and increasing something by 50% is not the same thing, that goes for any percentage,and are not equivalent, I is this correct?

Once again, your question is unclear. If you had a ton of crap in your yard, decreasing it by 50% and increasing it by 50% would both involve hauling a thousand pounds of crap. On the other hand . . .

[taper41]

I don't know I thought that was a good way to explain what I thought you and hotrod were getting at, that decreasing something by 50% is not the same thing as adding something meaning that its not an equivalent difference

[Geo]

Hey taper41,

Done your homework yet?  I want to check my answers. 

Geo

[tortoise]

My post 257 was not intended as a joke, or as punishment, but as a way for you to get a feel for the problem. There's no point going on if you're not willing to try. Getting things wrong is an essential part of learning.

I could have said . . .

To make a change in the value of a fractional expression, multiplying the numerator by x will have the same effect as multiplying the denominator by 1/x.

This is true, and a direct answer to your question, but I suspect will help you not at all.

[Glen]

Whats interesting is how everything changes when one builds a vehicle with all of this knowledge and design efforts only to find out once it hits the track the conditions don't always work. There will always be unknown issues.

[Geo]

My post 257 was not intended as a joke, or as punishment, but as a way for you to get a feel for the problem. There's no point going on if you're not willing to try. Getting things wrong is an essential part of learning.

Yes, I know why you placed the math to work examples there. I was hoping to nudge taper41 into giving answers, right or wrong. After all the knowledge a bit of a walk through the math would make it all come together. Thank you for both the info and example to work.    Thanks to all that contributed!

Looks like a lot of hot air from the student. I can get that from politics. Lots of restating the info without concrete data or plans.  Perhaps a change to BS in Political Science would be good. 

Geo

[Glen]

 

[taper41]

My post 257 was not intended as a joke, or as punishment, but as a way for you to get a feel for the problem. There's no point going on if you're not willing to try. Getting things wrong is an essential part of learning.

Yes, I know why you placed the math to work examples there. I was hoping to nudge taper41 into giving answers, right or wrong. After all the knowledge a bit of a walk through the math would make it all come together. Thank you for both the info and example to work.    Thanks to all that contributed!

Looks like a lot of hot air from the student. I can get that from politics. Lots of restating the info without concrete data or plans.  Perhaps a change to BS in Political Science would be good. 

Geo

hot air ? How so, I have yet poked fun of anyone nor act like i know anywhere near as much knowledge as what some folks on here have.

[tortoise]

Whats interesting is how everything changes when one builds a vehicle with all of this knowledge and design efforts only to find out once it hits the track the conditions don't always work. There will always be unknown issues.

"All this knowledge" certainly doesn't apply to me. If you use fastman's suggested method of building something that looks like other cars that work well, and just bringing a little more power to the game, you still have to figure what rear end will give you what revs at what speed. This kid can't do that.

[tortoise]

hot air ? How so[?]

I just began my program in auto aero design/ engineering.

[rgn]

I have yet poked fun of anyone

That is debatable.

nor act like i know anywhere near as much knowledge as what some folks on here have.

Speaking of condescension...   

[taper41]

I wish this discussion was held in person, unfortunately its not. So all I can really say is that I am not like that, and apologize if you come off that way .