It was Greek mathematician Archimedes (287 – 212 B.C.) who described that a body immersed in water, whether fully or partially submerged, experiences a upward force that is exactly equal to the weight of the water that body displaces. A pair of scales can show us weight in kgs (or lbs), which is more or less a translation of the gravitational force pulling an object downwards. An object in water experiences the same force, but it is also influenced by an opposite force, caused by the water pushing the object upwards. As a result, the weight of the object in water decreases as much as the weight of thedisplaced water. It would be easy to determine the nature of the three test rig materials, knowing their volume measures ’ principle!
Bear in mind that 1 litre (or dm³) of water weighs 1 kg. You should now be able to determine the specific gravity of every material or object including the ones in front of you!
(By the way: Physicists use Newton to define force. The displays therefore shows values in N instead of in kgs (or lbs). Not that it matters in this experiment though.)
1. Turn the hand wheel until the object is just about to touch the water. What’s the value in the display? Please, memorise that.
2. Turn the wheel again to immerse the object in the water. Make sure it’s fully submerged. Again, read and memorise the value displayed.
3. Determine the difference between both measured values
4. Divide the weight of the object (result no. 1) by the weight of the displaced water (result no.3)
5. Do you know now which materials are in the tubes?