Answer:
a) measure the change in volume when the object is immersed; compute from range data
b) find the ratio of mass to volume for a measured mass and volume
Explanation:
a) The volume of a small enough irregular body can be found by measuring the difference in volume of the (semi-)fluid in which it is immersed, before and after immersion.
For irregular bodies for which that approach does not work, various 3D scanners are available for measuring volume and surface area. They may rely on optical (laser or camera), sonic, or radar measurements, and generally involve computation from distances to various points.
__
b) Density is the ratio of mass to volume. So, measurements of mass and volume of a liquid sample are sufficient to provide the basis for determining density.
Other methods include measuring buoyancy forces, and/or the depth of submersion of something that floats in the liquid. For specific liquids, hydrometers are available for measuring their density relative to that of water.
