If I accelerate up to 100km/h really quickly in my massive V8, and nobody pats me on the back or passes me a beer in recognition of my achievement, does it still count!
richardmayes,
Nov 22, 10:40am
And re the original question -
Is your engine [more efficient], when it's making 200 horsepower, than it is when it's making 40 horsepower!
Or [less efficient]!
Or [just as efficient]!
Or [we don't know]!
sr2,
Nov 22, 10:45am
crzyhrse wrote: Not quite. The area under a time v speed chart is indeed distance. But that is not work because F = m x a and E = f x d (I know I said E = F x d / t above but I was away with the fairies - that's POWER which is the rate of work being done not work done). So E = m x a x x d. The masses are identical so we can drop that. That makes work proportional to the acceleration x distance. If you're accelerating at twice the rate you'll achieve the same speed in half the distance. So the work done is therefore the same. [quote]The area under the graph is the distance travelled, as we are not talking about a mass moving at a constant velocity with no resistance it equates to the input of energy i.e. energy consumed.
crzyhrse,
Nov 22, 11:40am
Energy is the (distance travelled x force). In this case one vehicle has twice the force over half the distance of the other - the energy used is the same.
crzyhrse,
Nov 22, 11:40am
Or understood it.
the-lada-dude,
Nov 22, 11:41am
sounds too good to be true CRZY i thought that the slower vehicle would be seeing wind resis 2x as long at every instant in time also to double your speed takes 4x the power P= M.V sqthis may affect the outcome !
crzyhrse,
Nov 22, 11:43am
Exactly. There's too many missing variables.
sr2,
Nov 22, 11:46am
Energy is distance travelled x force! Back to school young man!
crzyhrse,
Nov 22, 11:54am
Don't confuse Ek = ½mv² with acceleration which is F = m x a. They're not the same.
However, you've inadvertantly added further proof to my argument. The 'v' is the same value for either vehicle once they've achieved the same target speed or using the average speed, the 'm' is the same value for either vehicle. That makes the Ek the same value.
In what way is it not relevant! Work IS force x distance. There's no context where that is untrue.
The introduction of time is irrelevant until you're concerned with power which is the rate at which work is done. Power has no context here beyond determining acceleration.
the-lada-dude,
Nov 22, 1:53pm
there are no missing variables CRZYany variables are in the differences of time to reach60 mph and these variables that you can hang an efficiency on, adding all the efficiency'stogether + or - will give an overall rating that will point to a winner, that i suspect will cover 99% of vehicle matches
socram,
Nov 22, 1:58pm
My brain hurts.
smac,
Nov 22, 2:03pm
Y'what!
puslek,
Nov 22, 2:32pm
The fuel meter thinghy (km/l) in my car says if I accelerate easily I'd get higher km/l than if I accelerate quickly. Sure, the needle shows worse number more briefly as I get to the speed quicker than slowly accelerate to that same speed but, the average fuel consumption indicator would definately show worse number. It's ain't a precise instrument, but it can tell you the difference.
smac,
Nov 22, 2:40pm
Yes but that is as at a point in time - have you factored in the time you are using that amount of gas in each case!
the-lada-dude,
Nov 22, 3:39pm
and there it is ! PUSLEKyouv'e ruined the whole thread. yes a super accurate fuel flow meter on the identical vehicles and all other things being = would confirm the best fuel economyand that would allow test results using diff rpm, shift points, etc as long as they get to 60 mph in there allotted time .mmmmm. I see what you mean CRZYthere are lotsa variables,
sr2,
Nov 22, 3:41pm
LOL, I??
chrisdean007,
Nov 22, 4:33pm
a larger flywheel that takes longer to crank up might store more kinetic energy
smac,
Nov 22, 6:01pm
You think that flywheel gets spun up with some kinda free pixie dust!
crzyhrse,
Nov 22, 8:14pm
It's really very simple: we're discussing the energy used as in fuel burned. Time is not relevant to that discussion.
crzyhrse,
Nov 22, 8:15pm
The missing variables are the energy efficiency of that engine in the two different uses. Without knowing that the original question cannot be answered.
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