Stupid Physics Question

[devmach-e]

Irregardless of the energy density of gasoline, gasoline's energy has to be burned in an explosion to change the energy into a useful form of propulsion. Gas engines are usually only about 20%-25% efficient in producing useful energy, with 75%-80% of the energy wasted as heat...which causes global warming.

All of this wasted heat energy also requires gas cars to have large complicated cooling systems, to get rid of all this heat. All of this heat requires oil to lubricate parts, which then wears out from the heat, requiring replacement of oil and car parts.

Electric motors don't need to heat something to work, and are 90%-95% efficient. Gasoline is energy-dense, but hugely energy-wasteful. Electric motors don't damage the planet, and in states like California with 70% hydro-solar-wind generated power, generating the electricity is mostly non-polluting as well. Gas is a dead end.

California might have a decent amount of electricity from renewables, but it is nowhere near 70%. According to https://www.energy.ca.gov/data-repo...ty-data/2020-total-system-electric-generation it is closer to 45%. Even if you add nuclear, it only gets to about 55%.

Sponsored

 

[MW1515]

Right. I was going in that direction BUT a friend of mine keeps insisting that gasoline is the most efficient way to store energy (short of leveraging nuclear bonds). He references the energy density per kilogram. So, I’m trying to rationalize the amount of energy required to move a certain distance (I’m going to simplify the problem by saying both vehicles are using the same amount of energy and moving equal distances - yes, I know those are incorrect assumptions, but order of magnitude, they will work for this problem).

Your friend is 100% right that gasoline is more energy dense and can store more energy in a given volume than a battery, but is 100% wrong if he/she is trying to say that that makes it a better energy source for a vehicle, for all the reasons already mentioned plus quite a few more.

 

[AllenXS]

In case it is a serious question, the ICE would weigh a little over 100 pounds less.
With a drained battery, the MME will weigh somewhere between 8,600 and 26,000 pounds more.

It really depends on what kind of tow truck has come to get it. Either way, your ice cream is going to melt in the frunk.

And that’s why they put a drain hole there

 

[dml105]

He references the energy density per kilogram.

I’m assuming he is aware that the gasoline is not reusable?

 

[Maquis]

2.7*17=45.9. Unless you can find a 44.1 mile downhill stretch. I’ll be the ugly red truck blocking traffic along the main business street in either Kona or Hilo with that little gas. I’d be calling the tow truck a lot earlier driving my Tacoma that my Mach-e.

I’ll take the “less efficient storage” and more efficient energy conversion.

I didn’t may attention to the car referenced in the original post. I just figure a decent ICE car in the same class as the MME would be in the 30 MPG range.

 

[OH2AZ2OH]

E=mc^2 is valid in a nuclear reaction - i.e. nuclear fusion or nuclear fission. If any mass was converted to energy, we have a Hiroshima level problem - very, very, very bad. When there is no nuclear reaction, we revert to classical physics - in which matter is neither created or destroyed and energy is neither created nor destroyed (it just becomes less useful - all the chemical energy in the battery gets converted to heat - heat in the motors, the inverters, the tires, the brakes - if you stop really quickly, and most of all - friction with the air.). The battery doesn't gain or lose mass during charging or discharging. The anode and cathode of the battery change chemical composition during those processes - nothing else. Now, if you really want to pick nits, the tires lost some tread and weight slightly less after each trip, you may pick up some dirt as you drive, etc... But the battery does not change mass, and assuming you haven't moved it to the moon in the process and are thereby subject to a different gravitational force, weight doesn't change either.

E=mc^2 is valid in *all* cases. But, for practical purposes, it only matter in nuclear reactions. The amount of mass increase between a charged vs discharged MME is very, very, very difficult to detect, and essentially meaningless. But it is real.

https://www.abc.net.au/science/arti...mmon misconception,old-fashioned kick of ball.

 

[Garbone]

This is why Mr.Fushion in Back to the Future is believable. Our current efforts at converting mass to energy a very wasteful.

 

[Mach1E]

Your friend is 100% right that gasoline is more energy dense and can store more energy in a given volume than a battery, but is 100% wrong if he/she is trying to say that that makes it a better energy source for a vehicle, for all the reasons already mentioned plus quite a few more.

Actually the friend is right on both points……. For vehicles where energy density is important.

Airplanes and boats come to mind.

It would take around 12,000 lbs in batteries to replace the 100 gallons of fuel in my 23’ boat. That’s not going to work in a boat with a dry weight around 3600 lbs.

And flying NY to LA in an electric airplane carrying 300 passengers? Not with battery power.

Go figure we have a bunch of battery fanboys on a BEV forum. But sometimes it’s ok if your friend wins a single point in an argument.

 

[HuntingPudel]

A battery contains *electrical* energy as the result of a *chemical* reaction. The actual chemicals are not used up. The energy has no mass. The chemicals change state as energy is added or removed. The act of discharging a battery moves electrons one way through the circuit from one battery plate to the other. The a t of charging a battery moves the electrons from the second plate to the first. No mass is used or destroyed. There is no difference in weight.

 

[sotek2345]

Actually the friend is right on both points……. For vehicles where energy density is important.

Airplanes and boats come to mind.

It would take around 12,000 lbs in batteries to replace the 100 gallons of fuel in my 23’ boat. That’s not going to work in a boat with a dry weight around 3600 lbs.

And flying NY to LA in an electric airplane carrying 300 passengers? Not with battery power.

Go figure we have a bunch of battery fanboys on a BEV forum. But sometimes it’s ok if your friend wins a single point in an argument.

For larger boats/ships, nuclear is a great option from an engineering standpoint (maybe very large planes too). You just have to get around the security issue.

 

[drg1012]

E=mc^2 is valid in *all* cases. But, for practical purposes, it only matter in nuclear reactions. The amount of mass increase between a charged vs discharged MME is very, very, very difficult to detect, and essentially meaningless. But it is real.

https://www.abc.net.au/science/articles/2010/09/15/3011641.htm#:~:text=It's a really common misconception,old-fashioned kick of ball.

Did you know the earth was flat? The internet says so: 50 Reasons Why You Should Believe The Earth Is Flat (theodysseyonline.com) Regardless of what people post on-line, reality is reality. There is only a change in mass in a nuclear reaction. Your batteries are a closed system - for every electron that flows out of the anode, an electron flows back into the cathode. Nothing inside the battery transfers in or out. There is no change in mass.

 

[dtbaker61]

Your friend is right, to a point. Gasoline is about 100 times as energy dense as a Li-ion battery. But, a gas engine is only about 15-20% efficient(meaning 80% gets turned into heat and blown out into the atmosphere). An EV is 60-80% efficient, so it starts to balance out pretty quickly.

Most of the time, when someone is arguing in favor of ICE, they are very very selective in the attributes they consider, making it very difficult to have an effective conversation.

The energy 'density' of gasoline is indeed staggering.

It is nonsensical to compare to electrons.... which are neither 'created' or added, or 'destroyed' or depleted. They are just moved around in batteries. So your more accurate comparison is dependent on battery chemistry ( flooded lead-acid, AGM, Lion, LFP) when you talk about energy density.

The more direct comparison of ICE/BEV would probably be to include not only the weight of fuel (or batteries) tank, but the entire drivetrain as there is a significant difference in the total weight of motors, cooling systems, exhaust, etc.....

At the end of the day though, the same weight ICE vehicle will have a longer range than a comparable BEV because of the energy density of gasoline.

The REAL question is 'so what?'
We all know the days of gasoline powered autos for transportation are numbered. We also know that we will likely have to change our expectations to adjust to available technology.

 

[dtbaker61]

For larger boats/ships, nuclear is a great option from an engineering standpoint (maybe very large planes too). You just have to get around the security issue.

my bet is on biodiesel for trains, trucks, boats, planes (kerosene being one step from diesel). Algae-oil is promising, but a good 10 years out since most Algae research dollars are going into food and medicines

 

[AllenXS]

Actually the friend is right on both points……. For vehicles where energy density is important.

Airplanes and boats come to mind.

It would take around 12,000 lbs in batteries to replace the 100 gallons of fuel in my 23’ boat. That’s not going to work in a boat with a dry weight around 3600 lbs.

And flying NY to LA in an electric airplane carrying 300 passengers? Not with battery power.

Go figure we have a bunch of battery fanboys on a BEV forum. But sometimes it’s ok if your friend wins a single point in an argument.

Especially if you’re arguing who’s paying for the beers

 

[OH2AZ2OH]

Did you know the earth was flat? The internet says so: 50 Reasons Why You Should Believe The Earth Is Flat (theodysseyonline.com) Regardless of what people post on-line, reality is reality. There is only a change in mass in a nuclear reaction. Your batteries are a closed system - for every electron that flows out of the anode, an electron flows back into the cathode. Nothing inside the battery transfers in or out. There is no change in mass.

Einstein was occasionally wrong, and quite famously in the case of quantum mechanics. But not here.

https://physics.stackexchange.com/questions/196289/does-a-ticking-watch-have-more-mass

Sponsored