Water is a fundamental element in our lives, and understanding its specific weight is crucial in various scientific and engineering applications. Specific weight, denoted as γ (gamma), is defined as the weight per unit volume of a material. In this article, we will delve into the specifics of the specific weight of water, its formula, and its variations under different conditions.
Let’s explore this fundamental concept step by step.
- What is the Specific Weight of Water in m³ kg?
- What is the Specific Density of Water?
- What is the Specific Weight of Water in Ft?
- What is the Formula for the Specific Mass of Water?
- Density vs. Specific Weight and Specific Gravity
- Specific Weight of Water in kg/m³
- Specific Weight of Water Formula
- Specific Weight of Water in lb/ft³
- Specific Weight of Water in g/cm³
- Specific Weight of Water Symbol
- Specific Weight of Water in English Unit
- Specific Weight of Water in N/m³
- Example 1: Calculate Specific Weight of Water
- Example 2: Calculate Weight of Water in a Water Tank
- Conclusion
What is the Specific Weight of Water in m³ kg?
The specific weight of water in SI units is typically expressed in kilonewtons per cubic meter (kN/m³). It is calculated using the following formula:
γ (kN/m³) = ρ (kg/m³) x g (m/s²)
Where:
γ (gamma) is the specific weight in kN/m³.
ρ (rho) is the density of water in kg/m³.
g is the standard gravity, which is approximately 9.81 m/s² on Earth.
What is the Specific Density of Water?
Specific density is another term often used interchangeably with specific weight. Specific density is simply the reciprocal of specific weight and is expressed in units of m³/kg.
What is the Specific Weight of Water in Ft?
For those who prefer English units, the specific weight of water can also be expressed in pounds per cubic foot (lb/ft³). To convert from kN/m³ to lb/ft³, use the following conversion factor:
1 kN/m³ = 6.243 lb/ft³
What is the Formula for the Specific Mass of Water?
The formula for the specific mass of water is the inverse of specific density:
Specific Mass (m³/kg) = 1 / Specific Weight (kN/m³)
Density vs. Specific Weight and Specific Gravity
Before we proceed further, it’s essential to clarify the difference between density, specific weight, and specific gravity. Density (ρ) is the mass per unit volume and is expressed in kg/m³. Specific weight (γ) is the weight per unit volume and is expressed in kN/m³. Specific gravity (SG) is the ratio of the density of a substance to the density of a reference substance (usually water) at a specified temperature. It is a dimensionless quantity.
Specific Weight of Water in kg/m³
As mentioned earlier, the specific weight of water is 9.81 kN/m³ at standard gravity. This corresponds to a density of 1000 kg/m³.
Specific Weight of Water Formula
To reiterate, the formula for the specific weight of water is:
γ (kN/m³) = ρ (kg/m³) x g (m/s²)
Specific Weight of Water in lb/ft³
To calculate the specific weight of water in pounds per cubic foot, use the conversion factor:
1 kN/m³ = 6.243 lb/ft³
Specific Weight of Water in g/cm³
For the metric-minded, the specific weight of water in grams per cubic centimeter is equivalent to 0.00981 g/cm³.
Specific Weight of Water Symbol
In scientific notations, the symbol for specific weight (gamma) is represented as γ.
Specific Weight of Water in English Unit
In English units, the specific weight of water is expressed in pounds per cubic foot (lb/ft³).
Specific Weight of Water in N/m³
In SI units, specific weight is expressed in newtons per cubic meter (N/m³), which is equivalent to kN/m³.
Example 1: Calculate Specific Weight of Water
Suppose we want to calculate the specific weight of water at 4°C. Given that the density of water at this temperature is 1000 kg/m³, we can use the formula:
γ (kN/m³) = 1000 kg/m³ x 9.81 m/s² = 9810 N (9.81 kN)
Example 2: Calculate Weight of Water in a Water Tank
Imagine a water tank with dimensions of 5m x 5m x 3m. To find the weight of water in the tank, we calculate the volume first:
Total Volume = 5m x 5m x 3m = 75 m³
The total weight of the water is then determined by multiplying the volume by the density:
Weight of Water = 75 m³ x 1000 kg/m³ = 75000 kg
To convert this to kilonewtons:
Weight of Water in kN = 75000 N x 9.81 m/s² = 735750 N (735.75 kN)
Here’s the table for Specific weight of water
| Temperature (°F) | Temperature (°C) | Density (grams/cm3) | Density (kg/m3) | Specific Weight of Water (kN/m3) |
| -4°F | -20°C | 0.99355 | 993.55 | 9.747 |
| 14°F | -10°C | 0.99817 | 998.17 | 9.792 |
| 39.2°F | 4.0°C | 1 | 1000 | 9.810 |
| 40°F | 4.4°C | 0.99999 | 999.99 | 9.81 |
| 50°F | 10°C | 0.99975 | 999.75 | 9.808 |
| 60°F | 15.6°C | 0.99907 | 999.07 | 9.801 |
| 70°F | 21°C | 0.99802 | 998.02 | 9.791 |
| 80°F | 26.7°C | 0.99669 | 996.69 | 9.778 |
| 90°F | 32.2°C | 0.9951 | 995.1 | 9.762 |
| 100°F | 37.8°C | 0.99318 | 993.18 | 9.743 |
| 120°F | 48.9°C | 0.9887 | 988.7 | 9.699 |
| 140°F | 60°C | 0.98338 | 983.38 | 9.647 |
| 160°F | 71.1°C | 0.97729 | 977.29 | 9.587 |
| 180°F | 82.2°C | 0.97056 | 970.56 | 9.521 |
| 200°F | 93.3°C | 0.96333 | 963.33 | 9.450 |
| 212°F | 100°C | 0.95865 | 958.65 | 9.404 |
Conclusion
Understanding the specific weight of water is essential in various fields, including engineering, physics, and fluid dynamics. It allows us to calculate the weight of water under different conditions, which is valuable in designing structures and systems that involve water. Whether you’re working in SI units or English units, knowing how to calculate specific weight opens the door to a wide range of applications in science and engineering.
