Stupid Physics Question

[Mach1E]

I don't think what we are saying is all that far apart, I'm just a bit more optimistic about battery development and a bit more skeptical about hydrogen fuel cells. I would argue that even an incremental improvement in batteries (solid state reducing weight by half like you said), combined with reducing the amount of battery metals and minerals that need to be mined, combined with a transition from fossil fuels to renewables on the grid charging our batteries (already well underway) will lead to an absolutely ENORMOUS improvement in the environmental impact from transportation. I wouldn't call it battery tunnel vision, I'd call it being excited about the current revolution in automotive power generation . Let's meet back here in 10 years to discuss how things have progressed.

How about a PHEV where the generator runs on pure ethanol?

Honestly surprised the Chevy Volt design of hybrids didn’t gain more traction.

Electric car plus a generator for the rare times you need to travel far. Seems like the easiest compromise.

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[ctenidae]

How about a PHEV where the generator runs on pure ethanol?

Honestly surprised the Chevy Volt design of hybrids didn’t gain more traction.

Electric car plus a generator for the rare times you need to travel far. Seems like the easiest compromise.

Me, too- it works pretty well for trains. Of course, when Top Gear tried it they failed, and we know that's definitive.

 

[LTC_HUGH]

If I borrow my friend’s ICE Escape, fill the tank, weigh the vehicle, drive it until the vehicle stops running (I.e., is out of gas), then weigh it again, the vehicle will weigh a bit less. Specifically, it will weigh one tank full of gas less, or whatever about 15 gallons of gas weighs. (Anyone know where I’m going? )
If I fully charge my Mustang Mach E, weigh I, then drive it until it stops (I.e., drain the HVB), then weigh the car again, what will the difference in weight be?
What’s going on here?

no different

 

[DomiinUS]

no different

wrong..........
(but: unbelievable small.... as was discussed here before)

 

[Christina]

If I borrow my friend’s ICE Escape, fill the tank, weigh the vehicle, drive it until the vehicle stops running (I.e., is out of gas), then weigh it again, the vehicle will weigh a bit less. Specifically, it will weigh one tank full of gas less, or whatever about 15 gallons of gas weighs. (Anyone know where I’m going? )
If I fully charge my Mustang Mach E, weigh I, then drive it until it stops (I.e., drain the HVB), then weigh the car again, what will the difference in weight be?
What’s going on here?

I guess I'm not a Sheldon, I have no idea what we are talking about here. But my train was going 70mph and I got to the station five minutes early.

 

[ZuleMME]

wrong..........
(but: unbelievable small.... as was discussed here before)

I think this is a common misconception about potential energy vs matter/energy conversion. Chemical energy is not equivalent to energy that can be converted to matter.

A charged battery gives the illusion that the charge matters in regard to it's total atomic mass and thus it's weight. But it doesn't. When energy flows it's via electrons which all shift happily down the line one atom at a time but no atom is left without. The electrons flowing into the battery are exactly identical to those leaving. Same with electrons from the wall into the charger that are used to "push" lithium back across the barrier to "charge" the battery. But they don't stay, for every one used to push a lithium across another one leaves to go back into the wall. The total atomic mass does not change and thus the weight wouldn't change.

This is exactly what e=±mc² states should happen. If you split the atoms in the car in a fission reaction you'd get the same energy out before or after charging/discharging. Because you have the same atoms (albeit different electrons).

Note, don't stand near the car when you split it's atoms as it might be harmful to your health.

 

[DomiinUS]

I think this is a common misconception about potential energy vs matter/energy conversion. Chemical energy is not equivalent to energy that can be converted to matter.

A charged battery gives the illusion that the charge matters in regard to it's total atomic mass and thus it's weight. But it doesn't. When energy flows it's via electrons which all shift happily down the line one atom at a time but no atom is left without. The electrons flowing into the battery are exactly identical to those leaving. Same with electrons from the wall into the charger that are used to "push" lithium back across the barrier to "charge" the battery. But they don't stay, for every one used to push a lithium across another one leaves to go back into the wall. The total atomic mass does not change and thus the weight wouldn't change.

This is exactly what e=±mc² states should happen. If you split the atoms in the car in a fission reaction you'd get the same energy out before or after charging/discharging. Because you have the same atoms (albeit different electrons).

Note, don't stand near the car when you split it's atoms as it might be harmful to your health.

well - if you look at nuclear power, also there no electrons, protons or neutrons get lost, and you will still agree about the mass difference

Also in the battery, no electrons get lost anywhere. The weight difference is not caused by a loss of electrons (or gain of electrons), but due to the different state of energy the atoms and electrons are at depending on the state of charge.

(and yes, I know, for engineers this doesn't matter at all, it is no difference in real life - but for physicists it is there)

 

[ZuleMME]

well - if you look at nuclear power, also there no electrons, protons or neutrons get lost, and you will still agree about the mass difference

Also in the battery, no electrons get lost anywhere. The weight difference is not caused by a loss of electrons (or gain of electrons), but due to the different state of energy the atoms and electrons are at depending on the state of charge.

(and yes, I know, for engineers this doesn't matter at all, it is no difference in real life - but for physicists it is there)

Yet that is chemical differences but atomic mass is the same. Essentially imagine a wind-up toy. Does it weigh more wound up? No, same parts, different orientation. Same thing.

 

[timbop]

The OP wasn't talking about M=E/c^2.

He didn't consider that all the gasoline leaves the tank, bonds with atmospheric oxygen, and goes out of the tailpipe into the atmosphere - whereas all of the material in the EV battery stays in the battery.

 

[DomiinUS]

atomic mass is the same

not always.... that is exactly E=m*c^2

 

[AndrewY]

If I borrow my friend’s ICE Escape, fill the tank, weigh the vehicle, drive it until the vehicle stops running (I.e., is out of gas), then weigh it again, the vehicle will weigh a bit less. Specifically, it will weigh one tank full of gas less, or whatever about 15 gallons of gas weighs. (Anyone know where I’m going? )
If I fully charge my Mustang Mach E, weigh I, then drive it until it stops (I.e., drain the HVB), then weigh the car again, what will the difference in weight be?
What’s going on here?

Gasoline weighs approximately 6 lbs per gallon, though this varies by temperature.
Per https://energyeducation.ca/encyclopedia/Energy_density, gasoline stores 46 MJ/kg.
Per https://energyeducation.ca/encyclopedia/Energy_density_of_storage_devices, batteries store 30-200 Wh/kg, depending on battery type and other factors.
Per https://www.google.com/search?q=convert+MJ+to+Wh, there are 277.8 Watt-Hours (Wh) per 1 Megajoule (MJ).

So 1 kg of gas has 12777.8 Wh of energy, while 1 kg of batteries has 200 Wh, making gas about 64 times more energy dense by weight.

When you drive an ICE vehicle, the gas is burned, producing a variety of gasses, mostly CO2 and H2O, and energy, in the form of heat, noise and motion. The physical mass of the gasoline is converted to the physical mass of the gasses, which mostly go out the tail pipe. The total mass of the vehicle + fuel decreases by the mass of the fuel burned. For a 15 gallon tank, that's about 90 lbs.

When you drive an EV, there is a chemical reaction within the battery which produces energy, in the form of heat, noise and motion, but the physical mass does not change. Basically the electrons go out one side of the battery, through the circuit, and back into the other side of the battery. The total mass of the vehicle does not change.

The MME has a 91 kwh battery. At a mid-range energy density of 100 Wh/kg, that's 91,000/100*2.2 = 2002 lbs.

"Efficiency" is tricky, because it depends on exactly what you're measuring. In this case, the ICE vehicle and the EV each travel about the same distance, but the ICEV uses 90 lbs of "fuel" while the EV uses 2000 lbs of "fuel". (Aside: This is why I expect it'll be a long time before we see electric airplanes, but is less of a problem for land vehicles.)

None of this, however, accounts for the energy consumed to produce the gasoline, or the electric used to charge the battery.

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