# Finding mass using lever

deuterium
i was given a lab to find the mass of a meter stick using only a lever. Here's what the writeup says:

Problem: Find the mass of a meter stick. (No cheaters, no scales!)

Materials: Fulcrum, a 100 g mass, a mass hanger of mass 16.5 g, fulcrum pivot, meter stick.

Procedure: You are completely on your own to come up with on this one. (Hint: Remember that the mass of the meter stick acts like it comes completely from the center of gravity.)

Not exactly sure where to start with this one, though i think that you need to use torque. Any help will be appriciated, Thanks.

## Answers and Replies

Science Advisor
Gold Member
You should be able to balance the meter stick on the fulcrumat the center of the meter stick. Then you should hang the mass on the meter stick and move the meter stick until it balances again. You can then balance the torques to find the mass -->
mass of meter stick = m
mass of hanger plus 100g mass = M
distance between fulcrum and center of meter stick = d
distance between fulcrum and M = D

Set up a torque balance equation and find that:

mgd = MgD

So, with M known, you measure d and D and calculate m. You should repeat the experiment a number of times with the mass at different points to get a good experimental measure of m. For example, you could hang the weight at 5 cm intervals. position it correctly, measure, and calculate.

deuterium
Alright, i think i understand it now, thank you very much for the help.