 # Floating 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.

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Floating 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

 Measured in grams using a balance scale

 Measured in mL using a graduated cylinder

 Measured in cm 3 using math  Volume = L x W x H

 Measured in mL by using the displacement method

 g/mL Or  g/cm 3

 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?

2.9 g/cm 3 A piece of metal has a mass of 43.5 g and a volume of 15 cm 3. 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.

 Changes in density cause a submarine to dive, rise, or float.

 Ability to float  Ships are designed to have 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.

 The buoyant force works opposite the weight of an object.

 Archimedes’ principle states that the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces.

 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 cm 3

 What is the volume of the dinosaur?  5.6mL-4.8mL = 0.8mL

 If an object has a mass of 20 g and a volume of 40 cm 3, what is its density?  0.5 g/cm 3  Water has a density of 1.0 g/cm 3. If the object described above were placed in water, will it sink or float?  Float!

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