Density

 

Units -  kg/m3

 

Fluid: a substance that has definite mass but not definite shape.

Ex: gases and liquids Density: mass/volume

    

ρ Units: ρ water = 1 g / cm3 =

 __________kg/m2 = __________Kg/L

 Weight of a Fluid – force gravity exerts on a fluid = mg

Equation:

Specific Gravity - density of a fluid compared to the density of water.

Specific Gravity - comparison of the density of a substance with the density of water

Specific Gravity =

 

Alcohol or lead, which has a specific gravity of 11?

 

 

Pressure = F/A

 

N/m2 or Pascal

 

Pressure under a Liquid 

P0 – pressure above liquid

(Density in liq. depends only on h)

(Density depends only on h)

 

P0 – pressure above liquid

(usually atmospheric pressure)

 

at sea level

1 atm = 1.013 x 105 N/m2

Pascal’s Principle

If a force is applied on one place in an enclosed liquid the pressure increases everywhere else in the liquid.

 

F2 = A2
F1 A1

 

Giancoli p. 281) 14, 16 - 17

density of water = 1000 kg/m3

 

 

Buoyancy

"Archimedes Principle"

Why do some substances float in a liquid and some sink?

 

Objects that are less dense than the liquid sink.

 

The buoyancy force produced by a liquid is equal to the weight of the volume displaced

 

FB= Weight of fluid displaced= Weight of fluid displaced

FB = mg

Buoyancy force = submerged weight  

(rfluid)(Vsubmerged)g = mg

 

 

(rfluid)(Vsubmerged) = mobject

OR

Displ. Massliq. = Massobject

 

Gauge Pressure - fluid pressure w/o atmospheric pressure

Absolute Pressure - fluid pressure with atmospheric pressure

Fb = Weightair - Weightliq

 

Apparent Mass or Weight

- mass or weight in fluid

 

 

mg - mg = rVg
weight
in air

(apparent mass or weight)
  Mass of liquid displaced

 V of liquid displaced

= V of object submerged

 

 

Density / Part Submerged

 

Density Part Submerged
800 kg/m3



8/10 submerged
250 kg/m3






1/4 submerged
SG = .75








3/5 submerged








125 kg/m3



1/8 submerged
Density?
   

 

Partially Submerged /
Density and SG

 

 

Apparent
Mass or Weight in Liquid
= SG
Mass or Weight in Air

 

©Tony Mangiacapre., St. Mary's H.S., Manhasset, NY
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