Hi Andy - absolutely although the comment of "boring" (wink!) still applies. My
wife taught elementary school and they measured the height of a flagpole by
going to the end of the shadow and finding the angle with a home made astrolabe
and then measuring the shadow and then fiddling with these items to find the
height of the pole. I like the idea of finding length of a wall by comparing
image sizes of a given subject (could be a girl or a boy!) (wink!) but still it
is something that could be done by measuring on the ground. Getting them
enthralled is the hard part. Throwing a refrigerator out a 6th story window
might just do the trick! (another wink!)
I like the idea of the "fractions" though. Many (most?) _seniors_ in college
can't deal with them!
andy the elder
Andy wrote:
I was thinking the exact same thing, but I might add that you could used the same technique to then measure a feature on the building way up in the air like the gable or spire or clock or what ever might be unable to measure from the ground. Just have a child stand close to the building to get the scale factor. HAve the children guess what the size of the object is first; take a pole. The show them mathematically/geometrically what the real answer is. May be you could get the architect to provide a drawing to substantiate your answers...
Or maybe to take andys idea further. Use the girl to walk x distance along a wall parallel to the camera view, then 2x then 3x and use the shrinking size to measure the length of the wall.
Maybe, you could use the opportunity to explain fractions ie. how many children would it take to get to the top of the building or the length.
Have fun!!!
a different Andy
On Mar 10, 2010, at 5:41 PM, Hans Klemmer wrote:
Andy,
You never cease to amaze me!
Hans
On Mar 10, 2010, at 3:27 PM, ADavidhazy wrote:
As objects get farther from the camera their images diminish in size within the camera. Assuming a fixed focal length!
A given object twice as far as when it is near the camera will be 1/2 the size at the far distance as at the near one. This means you can determine the distance to objects as long as you know the distance to one of them (and they are all the same real size).
< op: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">So set up a camera with the library as a background and ask Suzy to stand 15 feet from the camera so you can see her from head to toe in the viewfinder. Make a picture. Then make another picture where she is farther from the camera ... wherever she wants to go. Make another picture. Or more for various positions.
Then measure her height on a print in the photograph made when she was 15 feet away. Let's say her image is 4 inches tall. Now look at the other prints (made at same magnification!) and measure her height in those. If in one of them she measures 2 inches then at that point she was 30 feet away.
If 1 inch she was e relationship is: Unknown Distance = Known distance multiplied by Image size at known distance divided by image size at unknown distance.
So what does this have to do with the library building which was supposed to be part of the project? The library construction serves as a nice background to the scene!
andy
It is good to be without vices, but it is not good to be without temptations.
-Walter Bagehot
