12.1. Pressure in Fluids http://www.ck12.org
FIGURE 12.8
the tank to the average pressure at the bottom of Lake Pontchartrain.
Answer:The pressure at the bottom of the tank is greater. No calculation is necessary since the depth of the water
tank is greater than the depth of Lake Pontchartrain. Remember that pressure gives force per unit area (how much
force a given area experiences). The fact that Lake Pontchartrain has 6.4 billion cubic meters of water compared to
the 1.3 cubic meters of water in the tank is irrelevant. The question to consider is: How much force does each square
meter at the bottom of Lake Pontchartrain experience?
Illustrative Example 3
A campsite has an open water storage tank whose bottom is elevated 3.00 m above a water faucet. The depth of
water in the tank is 1.25 meters.
a. Determine the water pressure at the bottom of the tank. See Figure 12.9.
Answer:
Since the water depth in the tank is 1.25 m
P 2 =ρgh= 1000 kgm 3
(
9. 81 ms 2)
( 1. 25 m) = 12 , 262. 5 → 1. 23 × (^104) mN 2 ,
b. Determine the water pressure at the faucet.
Answer;
The hose that runs between the water tank and the faucet has a vertical displacement of 3.00 m. The pressure at the
faucet is therefore no different than the pressure 4.25 m directly beneath the water level of the tank. (Imagine the
hose extending to the water level of the tank as inFigure12.10.)
The total elevation from the water surface to the faucet is 1. 25 m+ 3. 00 m= 4. 25 m.
The pressure at the faucet is difference in pressureP 2 −P 1. We setP 1 =0 sinceh= 0. 00 mandP 2 =ρgh=
(^1000) mkg 3
(
- (^81) sm 2
)
( 4. 25 m) = 41692. 5 → 4. 17 × (^104) mN 2