DENSITY

1
DENSITY

• Chapter 18
• Sections 2 3

2
Density

• Densitya measure of how much matter is squeezed
  into a given space
• The amount of mass per unit volume
• Density is NOT the same as mass
• Two objects can have the same mass, but not the
  same density
• 1 kg of iron and 1 kg of feathers have the same
  mass, but very different densities
• Two objects can have the same density, but not
  the same mass
• A cup of water and a gallon of water have the
  same density, but the gallon of water has more
  mass than the bucket
• Weight densitythe amount of weight a body has
  per unit volume

3
Density

• The planet Saturn has a mass of 5.69 x 1026 kg
  and a volume of 8.01 x 1023 m3. What is the
  density of Saturn? Would Saturn sink or float if
  you could place it in a gigantic bathtub filled
  with water (water has a density of 1000. kg/m3)?
• Diamond has a density of 3520 kg/m3. During a
  physics lab a diamond drops out of Virginias
  necklace and falls into her graduated cylinder
  filled with 5.00 x 10-5 m3 of water. This causes
  the water level to rise to the 5.05 x 10-5 m3
  mark. What is the mass of Virginias diamond?

4
Density

• What happens to the density of each piece of an
  object when it is cut into pieces?
• Each piece has the same density as the original
  object had
• Which has a greater density, a kilogram of lead
  or a kilogram of feathers?
• Any amount of lead is more dense than any amount
  of feathers.

5
Liquids

• Pressure

6
What is Pressure?

• Pressure is force per unit area
• P F/A
• Pressure in a liquid is also force per unit area
• Think about the pressure in the bottom of a
  beaker filled with liquid.
• P (weight of liquid)/(area of the bottom of
  beaker)
• The weight of the liquid is mg.
• The mass of the liquid depends on the density ?
  pm/V ? mpV
• P mg/A
• P pVg/A
• Volume depends on the area of the base times the
  height ? V Ah
• P pAhg/A
• P phg density x depth x gravity
• Liquid Pressure phg
• Total Pressure phg Patm
• Patm atmospheric pressure 1.013 x 105 Pa

7
Pressure Examples

• The water tank in the figure is 8 m above the
  tap. What pressure forces the water out from the
  tap? (Density of water 1000 kg/m3)
• Where is the pressure the greatestat the bottom
  of the large, shallow lake or at the bottom of
  the small, deep pond?

8
Pressure Examples (continued)

• Which teapot can hold more tea?
• Why is the water level the same in each vase?