I hate my Physics text

[Martin]

i can't figure out how to do the last one. i have no idea where i would get the info.

 

I think in that exercise the skill they want you to cultivate is a kind of quantitative visual thinking.

picture the front wall or side wall of a house in your neighborhood

just picture it in your mind and say what percent is glass

 

answering each of these questions should take around two to 5 seconds

if you are accustomed to making rough estimates (and have developed the skills---estimating visually etc.)

 

a long time friend of mind was an applied physicist at Stanford in the 1950s and 1960s and then in the electronics business. helped design and build accelerators including SLAC. He had 4 kids and he used to play exactly this game with them when they were going places in the car.

How many miles of road do you think there are in the US?

 

the idea is in the car you dont have any book, or internet access. you have to think based on just what you know and can see around you----the aim is to get within a factor of 10 or even 100. he was very fast at this himself, so he could tell what was a reasonable answer.

 

that particular guy is no more and his kids have grey hair, and i had lunch with 3 of the 4 last week and they were talking about those days and other stuff.

 

picture the wall of the house in your mind

visually slide all the windows to one side so the area is concentrated and forms some FRACTION of the total area,

recognize that fraction visually as whatever it is (one tenth, one fourth, one twentieth, one third, whatever)

 

convert that visual fraction into a percentage

 

if the whole thing takes more than 10 seconds and you are a typical American highschool student then something may have happened to the US educational system. Something may have died in the american brain, while we were busy getting overweight and watching football.

[MetaFrizzics]

Each question tests unique skills as well as general skills in reasoning.

 

They are designed to let the teacher see how you have creatively gone about solving each problem, which requires quite different techniques and presuppositions.

 

You can't just skip the calculations and fake up 'guesstimates', since if the teacher is any good at all, he'll be marking based upon your steps and calculations. The actual answers are irrelevant to both the purpose of the questions and THE MARKS.

 

For instance, you could approach question 3 very simply:

Take one wall of any standard house and calculate the area with a simple multiplication (width x height). Then count the windows and estimate their sizes (again w x h) and add them to get the total window area (w1 + w2...) for one average wall. Assume all houses regardless of size will have about the same window percentage, based upon the fact that the architectural designs are re-used over and over again, even by different developers when building suburban neighbourhoods. Make a simple fraction with (Window Area/Total Wall Area). Convert to percentage by ( x 100). Repeat for three different houses and then average the fractions. You average by adding the numerators and then dividing by the total number of samples ( (S1 + S2 + S3)/3 for example).

 

Some teachers will want you to take several samples, other may be happy with just one or two. You can 'fake' your results somewhat by taking different walls of the same house and saying they are different houses. You can even do this without leaving the house by simply looking at one wall of the room you're in and the size of window in it, then multiplying by the number of rooms on one wall of the house.

To get full marks, you should write down each basic step and say what your are doing and why briefly.

 

The other questions are also unique but easily solved with a little imagination.

[ydoaPs]

Are there no houses with windows close to where you live?

so a random house represents the average?

[timo]

If you´re smart enough to take a second attempt if the first building you randomly chose is a nuclear bunker, then yes. Most houses I´ve seen which I´d classify as "average house" do indeed have more or less the same number of windows per meter of wall and roughly the same height of the rooms.

As several people already pointed out: These kind of questions are about rough estimates, not about making statistics about the window-density distribution in US buildings.