游水一些疑問

甘e句"一般成年人體比重大約是0.95~0.97，在肺部充滿空氣時的比重則約為0.974"點解肺部充滿空氣個密度會大左?

This is apparent. The more air retained in the lung, the mass of the person would increase. Since density = mass/voume, a higher mass indicates a higher density.

""使肺中常充有空氣,有了氣就能使人更容易浮上水面"
甘佢個意思即系話吸氣戈陣個密度會細d?

In fact, the readiness to float may not increase much. As the statement in the above question already says that the increase is from 0.95~0.97 to 0.974, i.e. from 0.4%~2.5% only.

The only explanation is the a lung full with air will shift the centre of gravity of the person a little bit toward the head position. Together with the full-air lung which acts like a buoy, the posture of the persin in water tends to be in an up-right, the person would have the feeling that he floats more easily.

我唔知密度系咪等如比重

Specific gravity (比重) of an object is the ratio of the density of the object to that of water. Hence, specific gravity is a pure number (i.e. a dimensionless quantity).

In the old c.g.s unit, the density of water is 1 g/c.c. Hence, specific gravity of an object is numerically equal to its density in g/c.c.