Science Forum

FabianFnas
Science 17 Aug '09 05:58
1. 17 Aug '09 05:58
Scenario: I take my car out from my parking place, drive a while, uphill and downhill, stopping at red lights, starting at green lights, turning left and turning right, stopping at the supermarket, and go home agian ans put my car at the same parking place.

Question: Have all the energy consumed been converted to heat? Nothing else?

Question two: Does it matter if the engine was electrical or used petrol of some kind?

(These are not trick questions. A friend and I have different answers, and I want a second opinion.)
2. sonhouse
Fast and Curious
17 Aug '09 09:31
Originally posted by FabianFnas
Scenario: I take my car out from my parking place, drive a while, uphill and downhill, stopping at red lights, starting at green lights, turning left and turning right, stopping at the supermarket, and go home agian ans put my car at the same parking place.

Question: Have all the energy consumed been converted to heat? Nothing else?

Question two: Do ...[text shortened]... se are not trick questions. A friend and I have different answers, and I want a second opinion.)
I think there would be missing heat energy because the car will move the planet by some infintisemal amount which springs back in the local but would cause kinetic oscillations which would die down, hmm, maybe just converting to heat. But there would also be conversion of petrol to CO2 which would be a product that would be energy left over from the burning of the fuel. An electric car would presumably not do that so maybe all ITS energy would go into heat eventually. Some of the energy from both kinds of vehicles would end up tearing off bits of rubber from the tires which would be another form of energy not turned to heat. Ultimately it would seem 90 % would end up as heat at least.
3. 17 Aug '09 23:14
Originally posted by FabianFnas
Scenario: I take my car out from my parking place, drive a while, uphill and downhill, stopping at red lights, starting at green lights, turning left and turning right, stopping at the supermarket, and go home agian ans put my car at the same parking place.

Question: Have all the energy consumed been converted to heat? Nothing else?

Question two: Do ...[text shortened]... se are not trick questions. A friend and I have different answers, and I want a second opinion.)
If it was electrical, some of the braking engergy would go back to being electrical potential in the batteries. Besides moving the earth, the rest is converted to heat. There are some designs that use braking energy to spin a flywheel to store that energy and use it for acceleration. In that case, while the flywheel is spining some of the energy is converted to kinetic energy.
4. sonhouse
Fast and Curious
20 Aug '09 02:421 edit
Originally posted by joe beyser
If it was electrical, some of the braking engergy would go back to being electrical potential in the batteries. Besides moving the earth, the rest is converted to heat. There are some designs that use braking energy to spin a flywheel to store that energy and use it for acceleration. In that case, while the flywheel is spining some of the energy is converted to kinetic energy.
There is also the development by engineering students at MIT using shocks converted to generate electricity. It seems it can make 10% of the energy used to drive, so the whole thing gets 10% more efficient. It uses magnetics to generate power, as much as a full kilowatt from each shock, so the alternator can be removed which saves on fuel. It also absorbs shocks better than conventional hydraulic units. Here is one link:

http://engineering.suite101.com/article.cfm/shock_absorbers_that_generate_electricity
5. 20 Aug '09 02:59
Originally posted by sonhouse
There is also the development by engineering students at MIT using shocks converted to generate electricity. It seems it can make 10% of the energy used to drive, so the whole thing gets 10% more efficient. It uses magnetics to generate power, as much as a full kilowatt from each shock, so the alternator can be removed which saves on fuel. It also absorbs ...[text shortened]... e link:

http://engineering.suite101.com/article.cfm/shock_absorbers_that_generate_electricity
That would mean our suspension systems use up over 10 percent of the energy now. I would not have guessed it was even close to that. Interesting!
6. 20 Aug '09 05:451 edit
Originally posted by sonhouse
I think there would be missing heat energy because the car will move the planet by some infintisemal amount which springs back in the local but would cause kinetic oscillations which would die down, hmm, maybe just converting to heat. But there would also be conversion of petrol to CO2 which would be a product that would be energy left over from the burning ...[text shortened]... form of energy not turned to heat. Ultimately it would seem 90 % would end up as heat at least.
Your brought my thought on new lines.

My proposal: (P) "All ( 100% ) of the energy is converted to heat."

(1) We have some of the energy tat goes to wearing rubber and asphalt and break surfaces, molecule for molecule. During this process energy is used even if creates heat in the process. So the 100% in the proposal (P) is not excatly true, even if it's not much below 100%.

(2) When petrol are used forming CO2 and water (and stuff), we get energy as a difference between the chemical energy that is going in and the chemical energy that is going out the tube. This energy is converted into the desired movement, that's what the cars are for, but eventually turned into heat according to my proposal (P).

I say that 100% is not true, but how close to 100%? You said at least 90%, but I say at least 99% or even at least 99.9%, can this be true?
7. 20 Aug '09 10:42
Originally posted by joe beyser
That would mean our suspension systems use up over 10 percent of the energy now. I would not have guessed it was even close to that. Interesting!
Certainly on rough roads I can believe it as a bumpy road does slow a car down considerably. I guess that on a really bumpy road it could be over 50%. I wonder what sort of roads the 10% was calculated on.