# effeciency

### RP 3: Turn off daytime running lights, or reduce speed? Which saves more?

Which wastes more fuel? (and thus produces more carbon dioxide). This is a difficult to question to answer for a variety of reasons. The main reason is that a speed change from 71 mph to 70 mph is different than a reduction from 56 to 55 mph. First, let me be clear that the question of how much fuel is wasted using daytime running lights (or DRL as they are called) has already been addressed. The first source I found was howstuffworks.com Assumptions The daytime running lights on a car run at about 100 watts (for the pair) The energy density of gasoline is 1.21 x 108 Joules/gallon. A car is…

### ChevyVoltology 101

What's the deal with the Chevy Volt? Well, obviously, it is a cool car. A plug-in hybrid. The problem is in how to quantify its efficiency. Normal hybrids (the non-plug in type) have only one type of energy input, gasoline. The Volt can take gasoline or electricity input. This makes it difficult to compare the efficiency of other cars. What is efficiency? There are several things you could calculate. Actual MPG This is the distance the car travels (the miles part) divided by how much gasoline it used (the gallons part). Pretty straight forward? Ah ha! Not so straight forward for…

### How much would "free" energy cost you?

This was on my 'to do' list, but Tom at Swans on Tea beat me to it. Basically, this grocery store has these plates that when depressed produce electrical energy. Tom does a good job pointing out that this is not free energy (the original article says this also). Clearly, the energy comes from the cars. How much would this cost the cars? As always, let me start with some assumptions. The original article says that the bumps will generate 30 kW of energy every hour. That is an odd thing to say. I am going to interpret that as 30 kW of power for all hours (every hour). They couldn't have…

### Gas Mileage and Car Accessories (from Car Talk)

First: Car Talk is awesome. I wish I could come up with some class activities that help students become as good at trouble shooting and critical thinking as Tom and Ray are. Anyway, they are quite entertaining. So, my Dad called and told me he heard a discussion on Car Talk about the effect DC to AC converters and accessories plugged in to it and how they would effect gas mileage. I skimmed through the last Car Talk podcast, but couldn't find it. He must have heard a re-run on the radio or something (he doesn't really believe in podcasts). Let me calculate the effect a number of things…

### 90,000 KWhr for half a month

I just can't pass this up. One of the chemistry majors had a complaint with the power company. After an unusually high previous power bill, they checked the electric meter half way through the month. The meter said they had used 90,000 kilowatt-hrs of electricity. That is a lot of energy. It is also a lot of money. If I estimate 10 cents per kilowatt hour (the prices varies in space and time), this would be a \$9,000 bill. So, what is the deal? Is it a broken electric meter? Could be. If it is not, maybe it is a short. Shorts usually blow a fuse, but if it were an older house, could…

### Turn off daytime running lights, or reduce speed? Which saves more?

Which wastes more fuel? (and thus produces more carbon dioxide). This is a difficult to question to answer for a variety of reasons. The main reason is that a speed change from 71 mph to 70 mph is different than a reduction from 56 to 55 mph. First, let me be clear that the question of how much fuel is wasted using daytime running lights (or DRL as they are called) has already been addressed. The first source I found was howstuffworks.com **Assumptions** The daytime running lights on a car run at about 100 watts (for the pair) The energy density of gasoline is 1.21 x 108 Joules/gallon. A car…