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?They can be very close, or very far apart.
It depends on the particular mass distribution.
-----Original Message-----
From: chuck britton
Sent: Tuesday, February 01, 2011 4:38 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] real-world problem
hmm, how far apart are these two points??
At 4:23 PM -0500 2/1/11, Bob Sciamanda wrote:
?WRONG!
The center of mass point is NOT the same as the point which divides the
mass
in two.
-----Original Message-----
From: brian whatcott
Sent: Tuesday, February 01, 2011 3:24 PM
To: phys-l@carnot.physics.buffalo.edu
Subject: Re: [Phys-l] real-world problem
On 2/1/2011 1:08 PM, Paul Lulai wrote:
A source for interesting / fun problems that aren't necessarily physicsThe answer to a puzzle they asked two weeks ago would be helpful to
problems.
Car Talk Puzzlers. I haven't found a great way to implement them into
my
class, but they are fun. I am starting to post these questions and the
TPT Physics Question of the month for my students as extra credit
options.
I don't yet feel comfortable requiring a certain number of these
problems
to be solved in the course of a quarter. I might move in that direction
once I have a better feeling for how my students do with them.
< http://www.cartalk.com/content/puzzler/>
Paul Lulai
pre-calculus students.
The question:
How can I find the quarter full mark using a dipstick in a [horizontal
axis] cylindrical fuel tank as fitted to a truck?
The answer:
Cut a circle from card.
Draw a diameter, and a perpendicular radius.
[scroll down for spoiler.....]
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
Cut a semicircle out on the diameter line.
Balance the semicircle on the radius line with a pencil tip for the pivot.
This is the centroid of the shape, and represents the center of mass of
a similar cylinder - this is about 40% of the radial distance from the
center.
A stick marked with three lines scaled to the diameter of the fuel tank
in question
therefore fits the purpose. A mark at 70% of the diametrical length,
one at 50% of the diameter, and one at 30% of the diameter.
Brian W
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