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Richard Hanley
12-31-2006, 04:30 PM
When I was in high school shop class someone had made a 12 inch tool rest pattern. It was of pine and was painted flat black. From a few feet away it looked like it was made of cast iron. When we got some one new in the class room we loved to toss it to him and say “ catch”. With out exception the person had trouble catching it and was surprised that it was so light. In the short time he saw the pattern he identified the material [ incorrectly] - estimated the weight [ he must have estimated the volume in order to estimate the weight] and then caught it using that information.
Over the years I have handed a piece of bass wood or hickory to a child. most of the time he would lift it and say that the bass wood was light or the hickory was heavy. there again he was able to estimate the volume and what the weight should have been for average wood and then find out the true weight by holding it. And then know it was more or less then what the he was used to.
When I hand some one some thing small , most of the time they hold it in their upturned hand and move their hand up and down. When their hand is going up the part is heavier so it is easier to calculate the weight? how many things must he have to estimate in order to do this?
Some times they hold the part in their fist and move it back and forth , like they were shaking a bottle. Again making it seem to weight more to estimate it true weight?
This amazes me. Richard

BigBoy1
12-31-2006, 04:43 PM
I think you have stumblied upon on the many of life's imponderablies! I think it is akin to, "Why do we park in driveways and drive on parkways?"

Bill

Your Old Dog
12-31-2006, 04:50 PM
I think we use inertia like we use paralax in vision to judge distance.

Evan
12-31-2006, 05:17 PM
We do this through what is called our kinesthetic sense. It is something we learn very early and is a part of proprioception, the ability to judge where the parts of our body are without external reference such as vision.

The body keeps track of where it's limbs are via what amounts to an inertial guidance system that accepts feedback from neural sensors in the joints and muscles. This is why you can touch your nose with your eyes closed.

Comparing items by tossing them lightly creates a larger apparent difference in the momentary weight because of the acceleration and our kinestheic system is better able to detect that difference. That system is very sensitive to small accelerations as that is the primary method it uses to determine position, just like an accelerometer. It has very poor resolution in absolute terms. If you try touching your nose with your eyes closed, but do it very slowly, you will have no idea when your finger is about to touch your nose. That is because little information is provided to your brain about absolute position in the absence of detectable acceleration.

IOWOLF
12-31-2006, 07:19 PM
Evan, don't take this wrong but ,Why arent you teaching somewhere?
I swear I could listen to you for hours.
Honestly.Jay

wierdscience
12-31-2006, 07:44 PM
Anyone ever see the page about what is envolved in hitting a fastball?Interesting what must come together to perform what looks to be a simple task.

lane
12-31-2006, 09:30 PM
I`ll never forget When I was 16 I had a job bagging groceries . And came in one Sat. morning after being out Friday night drinking with my buddies still kind of hung over . Bagging a bunch of caned foodgrabed some cans to put in the sack and they went flying accross the store they were real lite some of those fried string potatoes you used to get in a can. Grabbing heavy cans and all of a sudden some lite ones and me still half drunk they went a flying.

dp
12-31-2006, 11:30 PM
Anyone ever see the page about what is envolved in hitting a fastball?Interesting what must come together to perform what looks to be a simple task.

Riding a motorcycle in a series of S turns with frequent braking and acceleration in off-camber turns (think Deal's Gap, Tennessee or the Bear Tooth Pass, Montana) is the same thing but in a third dimension - gyroscopic forces of the wheels and centripetal forces that require the bike to bank. The best example is a reducing radius turn in an uphill or downhill turn as in switchbacks on a mountain road. You really don't have time to think about your track, bank angle, and steering fork alignment. The ability of the human brain to reduce changing speeds over changing time (delta v/delta t) to a precise action on an 800 lb Harley-Davidson loaded and two up is amazing. Andfun !

The brake pedal of our cars would be useless without this ability.

Wirecutter
01-01-2007, 11:09 AM
Evan, don't take this wrong but ,Why arent you teaching somewhere?

Really. That was a good explaination - second only to the one about human memory being holographic. I'm not completely sure exactly what that means, but the characteristics fit - the bit about being able to lose information, yet still retain a coherent thought or memory over time.

...Or have you had long periods of time that allowed you to do nothing but sit and ponder things? Clearly the power of internet research came looking for you...

-Mark

Evan
01-01-2007, 12:15 PM
Or have you had long periods of time that allowed you to do nothing but sit and ponder things?


Well, I haven't spent much time in prison, if that's what you mean. :D

While the internet is certainly a boon for finding information it isn't the only source. I have a circle of friends and acquaintances that are well educated in a wide variety of disciplines and I don't hesitate to pick their brains when the opportunity arises. The reverse is true of course.

I take opportunities to learn that many people skip. Years ago when my son split open his scalp I asked the ER doctor to show me how to tie sutures. He was more than happy to demonstrate and also offered the interesting tidbit that including a bit of hair in the wound helps to promote binding and healing of the tissues.

My daughter's favorite question when she was two years old was "How do's it dad?"

Meaning of course, "how does it work?" Apparently that curiosity is hereditary.

joispoi
01-01-2007, 03:02 PM
I built a 500 sf deck out of Ipe or "iron wood". The Ipe was 5/4 x 6" and the joists were 2x12" PT yellow pine. Normally the pressure treated lumber feels like lead, but after moving the Ipe, the PT lumber felt like balsa wood.

And this has absolutely nothing to do with anything:)

Evan
01-01-2007, 04:51 PM
The first thing that came to mind when I read this was living in a rooming house with a common kitchen. Take out a quart carton of milk for cereal, leave it on the table, leave the kitchen for a few minutes to do something, come back in and pick up the nearly full carton to pour it on your cereal and damn near throw it on the ceiling 'cause it isn't full anymore.

I started punching a hole in the fold up pour spout and putting a small padlock on my milk cartons. :)

HTRN
01-01-2007, 08:22 PM
I built a 500 sf deck out of Ipe or "iron wood". The Ipe was 5/4 x 6" and the joists were 2x12" PT yellow pine. Normally the pressure treated lumber feels like lead, but after moving the Ipe, the PT lumber felt like balsa wood.

You might be interested to know that the Alantic City Boardwalk is made from Ipe'


HTRN