A colorful tail-spot wrasse (Halichoeres melanurus) is about 10 cm long and can float in the ocean with little effort, while a manta ray (Manta birostris) is more than 5 m across and must “flap” its fins continuously to keep from sinking. Which of these best explains the difference? A manta ray has (i) a different shape; (ii) greater mass; (iii) greater volume; (iv) a greater product of mass and volume; (v) a greater ratio of mass to volume.
Fluid Pressure
The term fluid pressure is coined as, the measurement of the force per unit area of a given surface of a closed container. It is a branch of physics that helps to study the properties of fluid under various conditions of force.
Gauge Pressure
Pressure is the physical force acting per unit area on a body; the applied force is perpendicular to the surface of the object per unit area. The air around us at sea level exerts a pressure (atmospheric pressure) of about 14.7 psi but this doesn’t seem to bother anyone as the bodily fluids are constantly pushing outwards with the same force but if one swims down into the ocean a few feet below the surface one can notice the difference, there is increased pressure on the eardrum, this is due to an increase in hydrostatic pressure.
A colorful tail-spot wrasse (Halichoeres
melanurus) is about 10 cm long and can
float in the ocean with little effort, while a
manta ray (Manta birostris) is more than
5 m across and must “flap” its fins continuously
to keep from sinking. Which of these
best explains the difference? A manta ray
has (i) a different shape; (ii) greater mass;
(iii) greater volume; (iv) a greater product of
mass and volume; (v) a greater ratio of mass
to volume.
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