Unit 3(Fluids), Chapter 8(Density describes the amount of mass in a

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Unit 3(Fluids), Chapter 8(Density describes the amount of mass in a given volume of a substance)-Reading ChecksLyndon Cobb
Reading Checks – Page 306
1. Explain what density means in your own words.
Density is the amount of mass in a certain volume; how tightly packed together the material is in a
substance
2. Explain why solids can support objects more easily than fluids can. You may use diagrams to help in
your explanation.
Attractive forces among the particles of a solid are stronger than those between fluid particles.
Therefore, particles in a solid cannot slide past each other or move between each other.
3. How can the density of a pure substance change? Provide an example.
As temperature increases, a substance will change from a solid, to liquid, to gas. The particle
theory states that the particles of a substance spread out as they gain energy when heated. Since they
spread out, the particles take up more space, which means that the density of a substance decreases. It is
almost always true that, for each pure substance (for example, silver), the density of its solid state is
greater than the density of its liquid state. The substance’s solid state and liquid state are, in turn, denser
than its gaseous state. Although most substances are denser in their solid form, water is an exception to
this rule. When water freezes, the particles move slightly farther apart as they become fixed in position.
This means that ice is actually less dense than liquid water, so it floats.
4. Using the particle theory, explain why some liquids can support a solid.
The particle theory of matter states that the particles in a substance are attracted to one another.
The strength of the attractive force depends on the type of particle. In some cases, the densities of two
substances can be so different that the liquid state of one is denser than the solid state of the other.
Therefore the attractive forces in the liquid state are stronger than the solid state of the other substance.
Examples of this are when the solid metals, copper, nickel, and silver, float on liquid mercury, which is
one of the densest substances known and therefore has some of the strongest attractive forces known..
Reading Checks – Page 315
1. What two measurements do you need to determine the density of a substance or object?
Density =Mass/Volume=gm/ml therefore we need mass (gm, kg, etc) & volume (mls, L, cm3)
2. What is the formula for density? Density =Mass/Volume
3. Describe how to measure the volume of an object with an irregular shape.
Displacement is the amount of space that an object takes up when placed in a fluid. So, by
measuring the displacement of an object, you can measure the volume of that object. So measure the
volume before the object is placed in it & the volume of fluid displaced when the object is placed in it.
The difference of the 2 volumes (or the volume displaced) is the volume of the irregular shaped object.
4. If the mass of a pure substance increases, what happens to the volume of the substance?
D=M/V, therefore the volume increases if the mass increases since V proportional to mass
(V=M/D).so for example if D=10g/L & mass=20g then volume=2L & if we increase the mass to 30g then
volume =M/D=30/10=3L, since D (density) doesn’t change (is constant) at a set temperature..
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