Have you heard of the term barometric pressure? what does it mean?

Barometric pressure is just the same as atmospheric pressure. It is called barometric pressure because the instrument used to measure is called barometer. It is the pressure exerted by the air at a certain altitude. Since it is the pressure exerted by the air, it is also known as the weight of the air above the Earth. Depending on the altitude at which the measurement is done, barometric or atmospheric pressure varies, but the barometric pressure at sea level is 1 atm (atmosphere). It is equivalent to 101325 Pa (Pascal), 760 torr, 760 mm Hg and 1.01325 bar.

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

Ais your answer to this