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# Specific gravity

In this video David explains what specific gravity means. He also shows how to calculate the value for specific gravity and use it to determine the percent of an object that will be submerged while floating. Created by David SantoPietro.

## Want to join the conversation?

• What if the specific gravity of the object is the same as the specific gravity of the liquid?
• This will mean that it will not sink,but fully submerge under the liquid-hovering!
• why does the fraction submerge underwater is the specific gravity ?
• For a particle to be in Translational Equilibrium,
Net force acting on the particle should be 0.
The forces on a particle in a liquid are buoyant force and it's weight mg.
mass=Volume*density
=>M=Vp*Dp (Vp=Volume of the particle, Dp=Density of the particle)
=>mg=Vp*Dp*g

Buoyant force=Vpi*Df*g (Vpi=Volume of the particle immersed, Df=Density of the fluid)
=>Vpi*Df*g=Vp*Dp*g
=>(Vpi/Vp)=(Dp/Df)
U know that Dp/Df is the specific gravity of the particle and Vpi/Vp is the fraction submerged under the fluid.
So, the fraction submerge underwater is the specific gravity.

Hope this helps :)
• In the beginning of the video, what it the large p respresent?
Pascals??
• I think its the lower case greek letter, rho, to describe density.
• What makes wood, and ice float in water?
• All objects have a buoyant force acting on them when they are in a fluid (gas or liquid) within a gravitational field. The gravity causes the fluid pressure to be greater the more downward you go. As a result a buoyant force pushing upwards is created from the larger pressure pushing on the bottom of the object versus the lower pressure pushing on the top. If the object has a larger downward force from gravity than the upward force from buoyancy, the object floats otherwise it will sink. All of this can be simplified to comparing the density of the object to the density of the fluid. If the object has higher density than the fluid, it will sink otherwise it will float.
• This might be a dumb question, but what's the name for the symbol to represent specific gravity? The one that looks like a p. Thanks!
• No dumb questions! The Greek lowercase letter rho ( ρ ) is usually used for density and specific gravity.
• Can an object with a specific gravity of 1 vary in how deep it is submerged or will it always just float directly beneath the surface of the fluid?
• Theoretically, the equilibrium is achieved with it floating just below de surface.
• Does specific gravity determine whether a human body will float? According to google the specific gravity of a human body is 1.01 so technically we should sink in water. What makes (some of us) float?
• Body fat has a specific density less than 1, so a person with more body fat will float. Also, the air in a person's lungs can act to make a person more buoyant.
• what if the liquid was made of a mixture of liquids with different densities
(1 vote)
• the liquid mixture with the specific gravity lesser than one will form a layer on top of the liquid while the liquid mixture with greater specific gravity will form a layer on the bottom of the liquid