If you haven't already, you may want to check this site out.
You'll be coming in late (it started 11/1) but there's still more than enough time. Starting tomorrow will mean 2174 words a day for 23 days to get to the 50000 word threshold.
Saturday, November 7, 2009
Friday, November 6, 2009
Evaluating the "half-tank" suggestion
A recent article here suggested that if a car weighed more, it would have less fuel efficiency. This seems intuitive, but then it also included a suggestion that fueling only half-tank at a time would be beneficial. Now it's time to see whether it is actually worth it for the time.
The article states that 100 pounds of reduced weight increases the mileage by 1-2%.
Assume that:
- the vehicle can hold 20 gallons (a minivan)
- has 25 mpg on average under normal circumstances; so every 500 miles, it requires refueling.
- the vehicle travels 10000 miles per year (i.e. 20 refuelings)
- in the "half-tank" situation, we only fuel 10 gallons at a time. Thus the vehicle will be 10 gallons, or around 70 pounds lighter. We'll say that this increases the mileage by 1%.
- gas costs $3 per gallon
- it takes 5 minutes to get fuel
However, this benefit of lower weight will only be applicable half the time. Right after refueling, the "full-tank" and "half-tank" vans hold 20 and 10 gallons. 10 gallons later, it's 10 and 0 gallons. The half tank van must refuel now, so we actually have 10 and 10 gallons. The benefit is gone!
Because the 1% works half the time, mathematically we can approximate it as .5% better mileage. So the half-tank vehicle will have an average of 25.13 mpg; it will travel 251.3 miles per tank, requiring 39.8 refuelings per year.
Now let's compare the costs:
Full tank:
- 20 times, 20 gallons each time, $3/gal = $1200
Half tank:
- 39.8 times, 10 gallons each time, $3/gal = $1194.
So you save $6 per year. Meanwhile, you needed
- 19.8 extra refuelings, 5 minutes each = 99 minutes = 1.65 hours.
Or, $3.64 per hour. Not exactly productive. Go full tank.
The article states that 100 pounds of reduced weight increases the mileage by 1-2%.
Assume that:
- the vehicle can hold 20 gallons (a minivan)
- has 25 mpg on average under normal circumstances; so every 500 miles, it requires refueling.
- the vehicle travels 10000 miles per year (i.e. 20 refuelings)
- in the "half-tank" situation, we only fuel 10 gallons at a time. Thus the vehicle will be 10 gallons, or around 70 pounds lighter. We'll say that this increases the mileage by 1%.
- gas costs $3 per gallon
- it takes 5 minutes to get fuel
However, this benefit of lower weight will only be applicable half the time. Right after refueling, the "full-tank" and "half-tank" vans hold 20 and 10 gallons. 10 gallons later, it's 10 and 0 gallons. The half tank van must refuel now, so we actually have 10 and 10 gallons. The benefit is gone!
Because the 1% works half the time, mathematically we can approximate it as .5% better mileage. So the half-tank vehicle will have an average of 25.13 mpg; it will travel 251.3 miles per tank, requiring 39.8 refuelings per year.
Now let's compare the costs:
Full tank:
- 20 times, 20 gallons each time, $3/gal = $1200
Half tank:
- 39.8 times, 10 gallons each time, $3/gal = $1194.
So you save $6 per year. Meanwhile, you needed
- 19.8 extra refuelings, 5 minutes each = 99 minutes = 1.65 hours.
Or, $3.64 per hour. Not exactly productive. Go full tank.
Wednesday, November 4, 2009
Americans don't know what investment is
I've always had this feeling that most people don't have the concept of investing: that you sacrifice something in the hope that it will return more in the future. However, after thinking a bit, I have realized that there is evidence of this everywhere.
The most obvious example is in our excessive spending. The average US citizen will spend $95 for every $100 dollars he gets. This works quite well for economy-stimulating tax cuts, but it is shocking how little Americans save. In fact, many people are in debt and instead of getting return on their money, they have to pay interest. The concept of bonds, bank accounts, and stocks seems quite foreign to people with their money.
The country itself isn't setting a good example either with a multi-trillion dollar debt. It seems that the US can borrow indefinitely, but the debt comes at a price: we must pay hundreds of billions of dollars of "debt service" per year, because of the interest associated with the debt! Although the US itself invests very well on its domestic programs, the efforts are partly counterbalanced by the large amount of interest we must pay yearly.
Economics isn't the only place that lacks investment. Think about in our schools, where some students simply don't learn. They are not aware that if they build a strong foundation of skills in high school, it will pay off for the rest of their lives. Indeed, we end up with city school districts with 30% graduation rates. If they had just stayed a year more with school (even with the bare minimum), they would have the potential to earn $10000 more per year for life. Another two years at a community college and the benefits are even better. But teenagers decide that school is too stressful and dropout, without truly realizing what they are doing to their future.
And investment isn't always long-term. Just look at homework completion. Why do people not do homework? I've never really understood the motives of some people. A single miss is forgivable, but consistent refusal to spend even 40 minutes a day on school work is mystifying. Easy points are thrown away, and everything else suffers as well, since students who don't do homework often perform poorly on tests. Every minute that a student spends on homework is an investment to get better grades and gain more knowledge, and it is sad to see that even a short-term reward requiring little work can be overlooked by many people.
The most obvious example is in our excessive spending. The average US citizen will spend $95 for every $100 dollars he gets. This works quite well for economy-stimulating tax cuts, but it is shocking how little Americans save. In fact, many people are in debt and instead of getting return on their money, they have to pay interest. The concept of bonds, bank accounts, and stocks seems quite foreign to people with their money.
The country itself isn't setting a good example either with a multi-trillion dollar debt. It seems that the US can borrow indefinitely, but the debt comes at a price: we must pay hundreds of billions of dollars of "debt service" per year, because of the interest associated with the debt! Although the US itself invests very well on its domestic programs, the efforts are partly counterbalanced by the large amount of interest we must pay yearly.
Economics isn't the only place that lacks investment. Think about in our schools, where some students simply don't learn. They are not aware that if they build a strong foundation of skills in high school, it will pay off for the rest of their lives. Indeed, we end up with city school districts with 30% graduation rates. If they had just stayed a year more with school (even with the bare minimum), they would have the potential to earn $10000 more per year for life. Another two years at a community college and the benefits are even better. But teenagers decide that school is too stressful and dropout, without truly realizing what they are doing to their future.
And investment isn't always long-term. Just look at homework completion. Why do people not do homework? I've never really understood the motives of some people. A single miss is forgivable, but consistent refusal to spend even 40 minutes a day on school work is mystifying. Easy points are thrown away, and everything else suffers as well, since students who don't do homework often perform poorly on tests. Every minute that a student spends on homework is an investment to get better grades and gain more knowledge, and it is sad to see that even a short-term reward requiring little work can be overlooked by many people.
Monday, November 2, 2009
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