we have to do this lab tomorrow. my teacher says that we have to "indirectly measure the radius" of a marble- he will only supply a ruler-plastic and a meter stick-wood

what am i supposed to do?

6 answers

Use the ruler to measure the circumference of the marble as accuratley as you can, then divide the circumference by 3.14159, or pi. That should give you your answer.
the ruler is hard- plastic... how do i do this?
he also said that we would need to use 11 marbles
I'm wondering if the fact that the prof is supplying TWO measuring units means the accuracy can be increased over that suggested by amir. How about this? Place the marble on the floor and against the wall. Place the ruler (or the meter stick) against the marble to hold it in place. Now place the other measuring device against the wall and the index of the first unit (the one holding the marble in place)will act as a marker for the other unit. Read that "mark." Your question suggests that the ruler will be in the every day units while the meter stick will measure in meters. If this is so, you can measure in inches or you can measure in meters, depending upon how the two ruler/stick are placed.
Now you've changed the rules. Doing it my way you only need to use one marble. But I suppose you could line 11 marbles up against the corner and go through the procedure.
I think this is playing with the body centered cubic model.

The body diagonal has a length that is four times the radius of the atom, R.

The relationship between a (the length of the side) and R can be worked out by the Pythagorean theorem:

(4 R)^2 = 3 a^2

Only need to set up the base (4 marbles and one on top and measure the length of the side.