Density (밀도)
Density is a physical property(성질) of matter(물질). Most commonly density refers either to the mass(질량) per unit volume (mass density) or the number of objects(물체) (e.g., atoms, molecules) per unit volume(단위부피당) (number density). We will focus out attention on mass density. The mass density has the units mass/volume. Since volume has the units length "cubed" then the SI unit of mass density is kg/m3. More common units of density are g/ml or g/l. Substances(순물질) have different densities. In fact the density of a substance can often be used to help identify it. Below is a table of densities of common materials(물질):
|
Densities of Some Common Substances | |
|
Substance |
Density (g/ml) |
|
ice (0 0C) |
0.917 |
|
water (4.0 0C) |
1.0000 |
|
gold |
19.31 |
|
helium (25 0C) |
0.000164 |
|
dry air (25 0C) |
0.001185 |
|
Human fat |
0.94 |
|
Cork |
0.22 - 0.26 |
|
table sugar |
1.59 |
|
balsa wood(발사나무) |
0.12 |
|
earth |
5.54 |
An important example is water. The above table(표) state that liquid water has a mass of 1 g in every ml. Thus 2 ml of water has a mass of 2 g etc.. Table sugar is more dense than water by about 60 percent.
Density does not depend upon size. For example the water in a swimming pool has the same density a glass of that swimming pool water.
Calculations with density are straightforward and involve the formula(공식) for density namely D = m/V, where D=density, m= mass and V = volume.
Example 1: What is the volume of a nugget of gold that has a mass of 3.45 g? The density of gold can be looked upon as a conversion factor from mass to volume i.e.,
3.45gAu x (1ml/19.31g) = 0.00179ml
Example 2: A light substance is found to weigh 23 g and to have a volume of 0.192 liters. What is the substance?
D = mass/volume = 23g/0.192L x L/1000ml = 0.12g/ml
Based upon this result we would guess that this substance might be balsa wood.
Example 3: What is the mass of 1 liter of sugar?
mass = density x volume = 1.59g/ml x 1L x 1000ml/L = 1590g
matter(물질); 공간을 채우고 있으며 질량을 가지고 있는 것
substance(순물질) 일정한 조성을 가지며 특징적인 성질을 가지는 것(원소, 화합물)
mass(질량); 물질의 양을 측정한 것