Calculating Specific Gravity in Water: A Step-by-Step Guide

In summary, the specific gravity of an unknown material can be found by using Archimedes' Principle or the Law of Buoyancy. By using the formula specific gravity = (density/density of water), and knowing that the density of water is 1000 kg/m^3, we can solve for the specific gravity by finding the volume of the material and its weight in both air and in water.
  • #1
davidatwayne
9
0

Homework Statement



A sample of an unkown material weighs 200 N in air and 150 N when immersed in water. What is the specific gravity of this material?

Homework Equations


specific gravity = (density/density of water)
density of water is 1000 kg/m^3


The Attempt at a Solution



I don't even know where to start. All my textbook says is the specific gravity of a substance is the ratio of its density to the density of the water at 4 degrees C. I don't know how to relate this to an equation or begin to solve it.
 
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  • #2
Hint: use Archimedes' Principle (or the Law of Buoyancy - a different name for the same thing)
 
  • #3
davidatwayne;1191839 A sample of an unkown material weighs 200 N in air and 150 N when immersed in water. What is the specific gravity of this material?[/QUOTE said:
The key is to solve one thing at a time and not try to make one big impossible equation.

The volume of this thing is related to 50N of water (200 - 150)
50 = (v)(d)(g)
50 = (v)(1)(9.8)
v = 5.102 litres i think

200 = (5.102)(d)(9.8)
d = ~4

You can also do it as an expression in one shot. The in-water weight is 150, which is related to (d-1), and your normal weight affected by d alone is 200. Put the stand alone conditions as the numerator on each side and the in-water as the denom.:
200/150 = d/(d-1)
d = 4
 
  • #4
Thanks a lot guys, it makes a lot more sense now.
 

1. What is specific gravity in water?

Specific gravity in water is a measure of the density of a substance compared to the density of water. It is a dimensionless quantity, meaning it has no units.

2. How is specific gravity in water calculated?

Specific gravity in water is calculated by dividing the density of a substance by the density of water. The result is a ratio that represents the relative density of the substance compared to water.

3. Why is specific gravity in water important?

Specific gravity in water is important because it can help determine the purity of a substance. Pure substances have a specific gravity of 1, while impure substances will have a higher or lower specific gravity.

4. How does temperature affect specific gravity in water?

Temperature does not have a significant effect on specific gravity in water. However, the density of water does change with temperature, so the specific gravity of a substance may vary slightly at different temperatures.

5. How is specific gravity in water used in industries?

Specific gravity in water is used in various industries, such as oil and gas, to determine the quality and purity of substances. It is also used in the production of beverages, such as beer and wine, to ensure consistency and quality in the final product.

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