Would going downhill make up for the gas used going uphill? (vehicle, fuel)
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This occurred to me today as I was driving home. There was a fairly steep stretch that by the sound of it looked like I am using a lot of gas. Then there was a similarly long stretch downhill. My question is did I make up for the uphill part going downhill? I have my own suspicions.
No the laws of physics regarding the conservation of energy say you can't break even. If you coasted down a 100 foot hill and coasted up a 100 foot hill you would not make it to the top. That is why no hill on a roller coaster is as high as the first drop.
To have a perfect balance in gasoline consumption you would have to go downhill with the engine shut off.
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Originally Posted by HappyRider
I am not sure this can be proven.
Yeah, I don't think the math would give you a perfect equality.
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Originally Posted by HappyRider
Where does the energy dissipated by the brakes come from and how is it accounted for?
If I remember correctly, the energy dissipated by the brakes (through friction, producing heat) comes from potential energy being converted to kinetic energy by the acceleration of gravity. But I was not the very best of physics students.
Bottom line, OP, if the engine is running you're using fuel whether you're coasting downhill or sitting still. Not running the engine on the way *up* the hill, on the other hand, would improve your mileage most of all!
This occurred to me today as I was driving home. There was a fairly steep stretch that by the sound of it looked like I am using a lot of gas. Then there was a similarly long stretch downhill. My question is did I make up for the uphill part going downhill? I have my own suspicions.
No, the short answer is you have friction from the tires on the ground, bearings in the wheels, the air......
Similarly this is why hooking a generator to you car powered by a wheel is pointless other than braking operations.
Last edited by thecoalman; 10-25-2014 at 05:39 AM..
No, the short answer is you have friction from the tires on the ground, bearings in the wheels, the air......
Similarly this is why hooking a generator to you car powered by a wheel is pointless other than braking operations.
Coalman's got it right- There are energy losses even when the vehicle is not moving, due to the friction in the motor and transmission- it takes constant energy input to keep those parts moving. Then, you have to add in the additional energy requirements to work against gravity to get the car to the top of the hill, plus the energy requirements to overcome the friction of the rest of the drive train, the tires, and the wind resistance (which increases in a non-linear fashion as velocity increases).
When you start down the hill, you have a certain amount of potential energy that is converted to kinetic energy, but even so, some of that energy is bled off from losses due to friction in the motor, the drive train, the tires on the road, and the increasing loss due to wind resistance as velocity increases (*very* simply speaking, the energy needed to overcome wind resistance (drag) will vary as the *cube* of velocity).
It obviously takes *less* fuel (energy input) to get down the hill than to get up it, but there will *always* be a net loss and it will never 'even out'.
No the laws of physics regarding the conservation of energy say you can't break even. If you coasted down a 100 foot hill and coasted up a 100 foot hill you would not make it to the top. That is why no hill on a roller coaster is as high as the first drop.
With gas economy Slow and steady wins the race. If you gun it to get up the hill you will use more gas than if you are just maintaining your speed.
I once heard that if you use cruise control you actually use more gas. Does that make sense?
Slow (the speed limit) and steady is the key.
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