What investigations never involve hypotheses?

The investigation that never involves a hypothesis is: a descriptive investigation. these investigations are used when little is known about a topic so you can't form a hypothesis. i hope this helps!

Exothermic,  physical change after it is already baked

The density of water is 1 g/cm cubed and in order for the pebble to sink its density has to be greater than the density of water and in order for the twig to float its density has to be less than the density of water