Floating and Sinking. Density is a measure of how closely packed the atoms in a substance are ...
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Notes 11-2Floating and Sinking
Density is a measure of how closely packed the atoms in a substance are
Density is a physical property
All matter has measurable density
Density = Mass Volume
Density
Measured in grams using a balance scale
Mass
Measured in mL using a graduated cylinder
Volume of liquids
Measured in cm3 using math
Volume = L x W x H
Volume of regular solid
Measured in mL by using the displacement method
Volume of irregular solid
g/mL
Or
g/cm3
Density Units
The density of a substance is its mass per unit of volume.
For example, a sample of liquid has a mass of 24 g and a volume of 16 mL. What is its density?
Calculating Density
Calculating Density
2.9 g/cm3
A piece of metal has a mass of 43.5 g and a volume of 15 cm3. What is its density?
Practice Problem
By comparing densities, you can predict whether an object will sink or float in a fluid.
An object that is more dense than the fluid it is in sinks.
An object that is less dense than the fluid it is in floats on the surface
An object with a density equal to that of the fluid floats at a constant depth.
Sink or Float?
Density Changes in density cause a submarine to
dive, rise, or float.
Density Changes in density cause a submarine to
dive, rise, or float.
Density Changes in density cause a submarine to
dive, rise, or float.
Ability to float Ships are designed to have buoyancy
Buoyancy
Buoyancy The pressure on the
bottom of a submerged object is greater than the pressure on the top. The result is a net force in the upward direction.
Buoyancy The buoyant force works opposite the
weight of an object.
Buoyancy Archimedes’ principle
states that the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces.
Buoyancy A solid block of steel sinks in water. A steel
ship with the same weight floats on the surface.
What is the volume of a box with the dimensions 8cm by 5cm by 5cm?
8cm x 5cm x 5cm = 200 cm3
Let’s Review!
What is the volume of the dinosaur?
5.6mL-4.8mL= 0.8mL
Let’s Review!
If an object has a mass of 20 g and a volume of 40 cm3, what is its density?
0.5 g/cm3
Water has a density of 1.0 g/cm3. If the object described above were placed in water, will it sink or float?
Float!
Let’s Review!