Density is described as the heaviness/ mass of an object for a unit volume. It is directly proportion to its weight. The weight of an object can be changed due to the gravity, but mass does not change. For an example if you measure the weight of a same object on the earth and moon you will have different readings from the both ends.
Gravity of the earth = 9.78 m/s2
Gravity of the moon = 1.622 m/s2
If we apply newton's third law for the situations, F=ma, here "m" is a constant as we use the same object.
Weight of the object on the earth = m * 9.78
Weight of the object on the moon = m* 1.622
From the above equations, you can understand that how the weight is being changed.
Density is calculated by bellow equation.
m = v.d (m = mass/ v = volume/ d = density)
hence, d = m/v (kg/m3)
Therefore, weight can be calculated for a particular material by bellow equation.
Weight = (volume of material) x (Density) x (Gravity)
Specific gravity of a material = d.g (g=gravity)
Therefore; Weight = (volume) x (specific gravity)
You can find the specific gravity of few of the materials bellow.
Aluminium Foil = 2700 - 2750
Beryllium = 1840
Brace = 8400 - 8730
Cast Iron = 6800 - 7800
Copper = 8930
Gold = 19320
Iron = 7850
Lead = 11340
Magnesium = 1738
Mercury = 13593
Nickel = 8800
Platinum = 21400
Silver = 10490
Tin = 7200
Titanium = 4500
Tungsten = 19600
Uranium = 18900
Zinc = 7135
Example questions:
[1] Calculate the weight of a solid iron cylinder dim. of 0.25m and height of 3m. (Find the specific gravity of iron in the above table)
Volume of cylinder = (22/7) x (0.25)^2 x 3
= say 0.6 m3
Weight of the cylinder = V. (specific gravity)
= 0.6 x 7850
= 4710 kg
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