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JDK1.0.2 simulations (1996-2001) => Dynamics => Topic started by: swimz on May 02, 2006, 01:14:43 pm



Title: law for levers
Post by: swimz on May 02, 2006, 01:14:43 pm
Hi found this question in a book and can seem to find any answers to it. So hpe u can help!
Archimedes is suppose to have said "give me a lever long enough and a fulcrum on which to place it, and I shall move the world." Explain the physics behind Archimedes thinking.

thanks :)


Title: topic363
Post by: Fu-Kwun Hwang on May 02, 2006, 02:17:56 pm
Hints:

 Torque = r X F

if r getting larger , then ...


Title: topic363
Post by: swimz on May 02, 2006, 04:20:29 pm
is "r" suppose to mean the distance?
torque is directy proportional to the distance and force.
so if r is getting larger, this means that the force will also increase. How does this relate to the question? :?:  lol
thanks


Title: topic363
Post by: Fu-Kwun Hwang on May 02, 2006, 05:22:42 pm
The mass of the earth is very large. You need a strong force to let the movement noticeable.

Torque = r1 X F1 = r2 XF2

If r1 is large enough, You can have very large F2 if r2 is small.  Or r1/r2>>1


Title: topic363
Post by: rhipple on May 02, 2006, 11:30:47 pm
I pondered this question a while ago. It boils down to replacing a large force acting through a short distance with a small force acting through a large distance.


Title: Re: law for levers
Post by: christit76 on February 22, 2007, 03:15:42 am
I have a question. I had an experiment using a meter stick, pencil (round without flat sides), quarter(new state one) and penny (1981 or later one).  I had to balance the meter stick on the pencil to find the center of gravity. It was 45.5. I then placed the quarter on 32 cm. To balance the quarter, I had to place the penny on 81 cm.  So c.g.= 45.5cm   x= 81cm
Equation reads as follows:
L1=c.g.-32=___-32,  L1=___cms
calculate L2= m1/m2 (L1)=____ (    );  L2=____cms
experimental L2=  x-c.g. when stick is balanced
L2=_____-______;  L2= _____ cms
                             (experimental)
Percentage error= larger-smaller/calculated value  x 100
Percentage error= (       )-(        )/(        )   x 100
Percentage error=_________%

I put 13.5 on the first blank and -18.5 on the second. On the m1/m2 blank, I put 32/81 (-18.5) ; L2=      -7.31   On the experimental L2= 81-45.5=35.5.  Please let me know if I am doing this correctly. I don't know even where to begin with the percentage error.  Can you please help????????????


Title: Re: law for levers
Post by: Fu-Kwun Hwang on February 22, 2007, 04:19:50 pm
You should have put 45.5 on the first black , which will give you L1=13.5 on the second. And you can work  out the rest.
For Percentage error: find the (larger and smaller value) from the (calculated L2 and experimental L2).