How do you make a simple microbalance?

Answer 1

a Fix the wooden strip to the wood block as illustrated using the elastic bands twisted twice round the block.

b Insert the small metal screw in one end of the drinking straw.

c Cut away the other end of the straw with scissors so that it acts both as a pointer and as a little scoop into which items to be weighed can be placed.

d Find the approximate centre of gravity by balancing the straw on the needle. Then push the needle through the straw to act as the rolling axle. It should be put through just above the long axis of the straw.

e Use standard masses (paper squares) to calibrate the microbalance. Mark the zero position of the pointer high up on the vertical scale. Put the 1 mm2 weight into the scoop and mark the pointer position. Continue adding weights until a uniform scale is constructed.

f Other things that might be weighed include a flake of mica, a small piece of thread, a small piece of iron wire before and after rusting, a drop of olive oil, and the loss in mass as a drop of ether evaporates.

g Order of magnitude calculations can be fun. Once the mass of a grain of sand is known estimate and then measure the mass of a beaker of sand.