What instrument measures the volume of a plastic block?

Answer 1

Easiest way is to fill a kitchen measuring container to the top with water. Now slowly immerse the plastic block into the water and collect every drop of water that overflows when you do this. Having collected this overflow, measure its quantity by pouring every drop of it into a measuring container. This collected overflow represents precisely the volume of the plastic block.

The number of millilitre (ml) you collected will be the number of Cubic Centimetres of volume of the plastic block. Remember always, that ml = cc . In other words 1 millilitre of fluid occupies exactly 1 cubic centimetre of volume. Now you see why the Metric system is so commonly used , and is so simple to use.
A ruler could be used to measure the dimensions- if the plastic block were a regular straight sided object whose volume was easy to calculate. The calculation would be simple for a cube or rectangular prism, but could be quite complicated for other shapes.

Archimedes came up with the best solution when he invented the Eureka jar. This is a vessel with carefully positioned overflow tube which allows any displaced water from the fully filled vessel to be collected.

If you fill a Eureka jar to the point where it is about to overflow, then place the plastic block in in the jar (if it floats one would need to press it under the water with a piece if thin wire (whose volume is negligible) and collect all the water that overflows in a measuring cylinder - that is assuming the object is small and not the size of a family car. The volume of water collected will equal the volume of the plastic block.