Question

why doex an object float or sink when placed on the surface of water

Answer 1

this is due to buoyancy which is directly proportional to mass.You can also state archimedes principle fro extra marks

Answer 2

HI HERE IS THE ANSWER
WHEN THE DENSITY OF A SUBSTANCE IS LESS THAN WATER IT FLOWS ON THE SURFACE OF WATER .
WHEN THE DENSITY OF A SUBSTANCE IS HIGH THAN WATER IT SINKS INTO WATER .