1. ## Fuel efficiency

Is my car really fuel efficient??
While taking a curve going up a hill with the cruise control disengaged and my foot off the accelerator pedal, The vehicle still accelerates.

<span style="background-color: #FFFF00; color: #FFFF00; font-weight: bold">If not traveling in a straight line an object is accelerating towards the centre of the circle described by its path.</span hide>

2. ## Re: Fuel efficiency

If you like weird motion phenomena, try stopping your car then letting it roll on Electric Brae in Scotland. Most unnerving!

Alan

3. ## Re: Fuel efficiency

Although not as long, this is closer to my home

And this to yours.

4. ## Re: Fuel efficiency

If your foot is off the pedal, and the cruise control is disengaged, then the car is certain to be slowing down.

Slowing down is also acceleration, using the technical definition needed to include centripetal acceleration as acceleration.

Good point.

6. ## Re: Fuel efficiency

This is an interesting problem I'd never looked at in detail. For a car slowing as described, on an uphill incline with radius of curvature r, I calculate the acceleration a relates to the centripetal and tangential accelerations as follows:

7. ## Re: Fuel efficiency

> I calculate the acceleration a relates to the centripetal and tangential accelerations as follows

[devil's advocate smiley]...... and just because "you lot" have caught me out before[/devil's advocate smiley]

Relative to what Mssrs. Miller, Wells and Hutchinson? <img src=/S/evilgrin.gif border=0 alt=evilgrin width=15 height=15>

It will get very complicated when we bring in further tangents and centripetal forces, shall I begin:

1) Earth Orbit around Sol
2) Sol Orbit around centre of the Milky Way
3) The orbit of the Milky Way around the centre of the universe

<img src=/S/flee.gif border=0 alt=flee width=25 height=25>

8. ## Re: Fuel efficiency

Not Mr. Wells, since he's driving and in an accelerated frame of reference. But approximating the Earth as an inertial reference frame, the accelerations will remain the same in any of the other (approximately inertial) frames of reference you mention. Acceleration is not "relative". <img src=/S/evilgrin.gif border=0 alt=evilgrin width=15 height=15> I guess you could account for the factors you mention and would end up with a different answer at the fifth decimal place... which wouldn't be that significant since we'd be lucky to be able to measure accurately to three places.

OTOH, if Mr. Wells took up firing long range artillery shells as a new hobby, then we'd probably have to account for Coriolis forces, lest they land in the wrong neighbour's backyard. <img src=/S/bouncenburn.gif border=0 alt=bouncenburn width=31 height=31>

Alan

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