You can use specific gravity to calculate pressure exerted by a fluid by multiplying the specific gravity of the liquid by the density of water and the height of the liquid column.
Understanding Specific Gravity and Pressure
Specific gravity is a dimensionless quantity, representing the ratio of a substance's density to the density of a reference substance (usually water at 4°C). It indicates how much denser or less dense a substance is compared to water. Pressure, on the other hand, is the force applied perpendicularly to the surface of an object per unit area. In fluids, pressure increases with depth due to the weight of the fluid above.
Calculating Pressure Using Specific Gravity
The video reference states that pressure is determined using the following formula:
Pressure = Specific Gravity * Density of Water * HeightWhere:
- Pressure: The force exerted per unit area (typically in Pascals or psi).
- Specific Gravity (SG): The ratio of the density of a substance to the density of water (dimensionless).
- Density of Water (ρwater): The density of water, which is approximately 1000 kg/m³ or 62.4 lb/ft³.
- Height (h): The depth of the liquid column, typically in meters or feet.
Practical Application:
- Identify the Fluid: Determine the specific gravity of the fluid you are working with.
- Measure Height: Measure the height or depth of the liquid column.
- Apply the Formula: Input the specific gravity, density of water, and height into the formula.
- Calculate Pressure: Compute the resulting pressure exerted by the liquid.
Example:
Let's say you have a fluid with a specific gravity of 1.2 and a height of 5 meters:
- Specific gravity (SG) = 1.2
- Density of water (ρwater) = 1000 kg/m³
- Height (h) = 5 m
Plugging these values into the formula:
Pressure = 1.2 1000 kg/m³ 5 m
Pressure = 6000 Pascals
Why This Formula Works:
This method directly links specific gravity with pressure calculation. Since specific gravity compares the density of a liquid with water, the formula effectively adjusts the density of water by the specific gravity of the liquid in question and then applies the fluid pressure formula.
Key Points:
- Specific gravity is a ratio and does not have units.
- The density of water is a constant in this formula, but it must be in the correct units to match the other variables.
- The height should be a vertical measurement for the formula to be accurate.
Table: Variables for pressure calculation with specific gravity.
| Variable | Description | Units |
|---|---|---|
| P | Pressure | Pascals (Pa), psi |
| SG | Specific Gravity | None |
| ρwater | Density of Water | kg/m3, lb/ft3 |
| h | Height | m, ft |
