Laboratory work. Measuring the mass of a body with a beam balance
You need: a beam balance with weights, a beaker, water, and cube-, ball- and cylinder-shaped bodies. First the balance is set in equilibrium (if needed, bits of paper are put on the pans). The body to be measured goes on the left pan and the weights on the right pan; weights are chosen close to the mass of the body, because a much too heavy weight can damage the balance. Wet, dirty or hot bodies must not be put on a pan, and liquids or loose substances (salt, sugar) must not be put on without a container; nothing heavier than the rated load in the balance’s passport may be weighed. Small weights are taken only with tweezers, because moisture and grease from the hand change their mass. At equilibrium the sum of the masses of the weights on the pan is the mass of the body. The mass of water is found by the difference method: weigh the empty beaker m₁ and the beaker with water m₂, then m(water) = m₂ − m₁.
Laboratory work (in pairs): (1) bring the balance to equilibrium; (2) measure the mass of the empty beaker; (3) add 100 ml of water and measure again; (4) find the mass of water and check that it is close to 100 g (1 ml of water ≈ 1 g). Safety: do not spill water on the pan; handle glassware carefully; take weights only with tweezers.