Hybrid Cars/ A Way to Extricate Ourselves from Oil

Chumly wrote:

BTW it is simply not accurate to say "its a fact that heavy objects take more power to accelerate them and stop them than lighter ones."

Why?

- Because wieght is a funtion of gravity, so mass is the more correct term here not weight.

- Because a more masive object only takes more power to accelerate and decelerate than a less massive object if the relative delta V's are taken into account.

Its perfectly correct to say heavier objects. Weight is a function of the acceleration due to gravity and mass. And as gravity can be taken as uniform over the surface of the earth, for all practical purposes, weight and mass are synonymous.

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Nope not synonymous at all, not even on the surface of the earth because a body under the influence of delta V on the surface of the earth means a change in weight while said body's mass remains constant; this is in fact easily and commonly achievable!

Let alone the obvious fact that the entire universe does not reside on the Earth's surface, let alone the fact that Newtonian Physics has predictive limitations when said body approaches C!

Thus in many ways I must disagree, and quite logically too!

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Chumly wrote:

a body under the influence of delta V on the surface of the earth means a change in weight..

Not necessarily. We were talking about cars. An accelerating car weighs more than it does at the traffic lights? I dont think so. Seen any signs saying WEAK BRIDGE NO ACCELERATING? Is a car's traction changed depending on whether its accelerating or braking? I said for practical purposes weight and mass are synonymous. I am well aware of the definition of the two terms.

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You are forgetting about lateral forces as expressed by +/- G's under the influence of delta V! So yes there is a change in the car's weight in the referenced dimension!

You have not argued successfully that "weight and mass are synonymous".

And nope you did not say "for practical purposes, weight and mass are synonymous" you said "for all practical purposes, weight and mass are synonymous". A diving bird would disagree (if a bird could disagree!).

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acceleration is a vector quantity having both magnitude and direction. Not dimension.

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The referenced dimension I referred to is "lateral" and not that acceleration is a dimension. I could take that as humor on your part though!

And actually acceleration (better termed from a forces point of view as delta V because it then encompasses both acceleration and deceleration) is a more than simply a "vector quantity having both magnitude and direction" because it encompasses change in velocity over time. Thus you left out the parameter of change in velocity over time in your vector refernce.

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The rate of change over time of velocity (itself a vector) is acceleration (another vector). Velocity and acceleration can have positive or negative magnitude.

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And your last post supports your claim that "for all practical purposes, weight and mass are synonymous" how precisely Mr. Feet per Second Squared?

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well days ago, God it seems like years, you were going on about cars fuel consumption being related to suspension characteristics rather than weight.

I merely pointed out that weight is a significant factor in determining consumption.

You took exception to this because strictly speaking it is mass not weight that determines the force required to accelerate.

I maintain cars accelerate in a direction normal to the force of gravity, and thus for all practical purposes the weight of a car can be taken as its mass when calculating the affect on fuel consumption.

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Steve 41oo wrote:

well days ago, God it seems like years, you were going on about cars fuel consumption being related to suspension characteristics rather than weight.

Nope I did not claim consumption was related to suspension characteristics. Your imagination is working overtime! Back up your claim by quoting me as such.

Steve 41oo wrote:

I merely pointed out that weight is a significant factor in determining consumption.

I certainly never disagreed with that assertion, and if you claim I did disagree quote me as such. In fact you said a lot more than "merely pointed out that weight is a significant factor in determining consumption" you said "for all practical purposes, weight and mass are synonymous" among other claims.

Steve 41oo wrote:

You took exception to this because strictly speaking it is mass not weight that determines the force required to accelerate.

I did not take exception to the fact that power to weight ratio plays a part in fuel consumption, if you believe I did then quote me as such.

Steve 41oo wrote:

I maintain cars accelerate in a direction normal to the force of gravity, and thus for all practical purposes the weight of a car can be taken as its mass when calculating the affect on fuel consumption.

Be that as it may your claim "for all practical purposes, weight and mass are synonymous" goes far beyond those self limiting parameters and as discussed you have not argued successfully that "for all practical purposes, weight and mass are synonymous".

This thread is getting silly!

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You're both dancing around the same thing. Weight and mass are not synonymous, but on earth they will (for all intents and purposes) be proportional directly.

Mass is mass, irrespective of gravity. Gravity is what gives mass its weight, so while saying that mass and weight are the same is technically untrue, I understand what was being said.

And yes, all things equal, a heavier car will require more fuel to get it up to speed, but not require any more to maintain it.

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Don't spoil our fun!

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curtis73 wrote:

And yes, all things equal, a heavier car will require more fuel to get it up to speed, but not require any more to maintain it.

you show me a "heavier car" having the same frontal area as a lighter car. And even if its long and thin and heavy, drag coefficient is poorer. Lighter cars offer less drag and hence use less fuel at the same speed. Smile

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No... I said all things equal.

Take a Honda Accord with just a driver in it. Accelerate to 60 mph.

Now do the same experiment with two 200-lb passengers in the car. The second test will use more fuel to achieve 60 mph, but once there it will consume the same fuel to maintain it.

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curtis73 wrote:

.........but once there it will consume the same fuel to maintain it.

Nope "once there" it will not "consume the same fuel to maintain it" because the rolling friction of pneumatic tires is to some degree a function of the load, this is also the case with some of the other frictional loads such as wheel bearings.

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agreed, but again I was hoping that was covered by "all things equal" including pneumatic trail, bearing friction, yadda yadda.... I admit the analogy was poorly constructed. Smile

Stop yelling at me Laughing

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"all things equal" is such a messy and hopeful idealism, and in any case it's much harder to be a smart-ass if I abide by that.

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no one spotted my deliberate ( Embarrassed

) error?

magnitude cannot by definition be negative

ok back to the yellin Laughing

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Hybrid Cars/ A Way to Extricate Ourselves from Oil

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