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

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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!

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