Properties of Matter(Viscosity, Density, and Buoyancy) Notes

VISCOSITY

Viscosity: measure of afluid’s resistance to flow

Fluid: a liquid or a gas

  • This property is important in producing goods such as food and motor oils.
  • This is determined by the size and shape of its molecules.
  • If molecules are large and have bumpy surfaces, a great deal of friction is created as the molecules slide past one another which increases the viscosity. A liquid with large molecules and bumpy surfaces flows at a slower rate than a liquid made up of small molecules with a smoother surface.

Look at the oil molecule and water molecule.

Which type of molecule would be easier to pour from a bottle? ______ WHY?______

______

  • As temperature of a LIQUID increases, its viscosity decreases.
  • The additional kinetic energy allows the molecules

to slide past each other with greater ease.

  • As the temperature of a GASincreases, its viscosity increases.
  • Because gas molecules are far apart, they do not

have to slide over each other very often in order

to flow.

  • Raising the temperature actually increases the number of collisions between the molecules, resulting in an increase in frictionand therefore, viscosity.

Examples:

In other words...

Heat ‘em up, Speed ‘em up!!!

DENSITY

Density: the measure of how tightly packed the atoms of a substance are

  • Mass per unit volume

Let’s Think:

  • A ping pong ball and a golf ball are approximately the same size.

Which one is more dense?______

The density of an object could be increased in two ways:

  • if you cram more matter into a particular volume of space (increase mass) or
  • if you cram the matter you have into a smaller volume of space (decrease volume—which you could do with a gas).

Let’s do some math!!!

*Remember: To get full credit, you need to show your work!!*

EX:

a)Find the density of a 45 g object that has a volume of 15 mL?

b)If an object has a density of 2 g/mL and a mass of 20 g, what is the volume?

c)Find the mass of object that has a density of 5 g/mL and a volume of 10 mL?

What is the mass in kg?

Density of States of Matter

You already know about the three most common states of matter (solid, liquid, and gas). How does the density of a substance changewhen it changes temperature or changes its state of matter?

Q:Which is more dense a liquid or a solid?
A:We learned that the molecules in solids are closer together.This is why solids are more dense. Liquids slide around and are less closely packed. Liquids are less dense than solids.
***Not all solids are denser than liquids. There is one great and important exception.What is it?

Water is more dense as a liquid than a solid. And good thing, too! Many forms of life depend on ice being less dense.
Name one:
Q: Which is more dense a liquid or a gas? (Hint: think about how tightly packed the molecules are.)
A: / Find the density of water:
Mass =
Volume=
Density=


List the densities of 3 objects/substances andrecord if they float or sink in water based on their density.
Density: Sink or Float?
Wood block:
Penny:
Olive Oil:
What did you find out about floating or sinking substances and density?
Q:If an object has a density of 1.35 g/mL, will it float or sink in water?
A:
Density of Some Common Substances / Substance / Air / Olive Oil / Wood (Oak) / Ice / Water / Salt Water / Bricks / Penny
Density (g/cm3) / 0.0013 g/cm3 / 0.918 g/cm3 / 0.6 - 0.9 g/cm3 / 0.92 g/cm3 / 1.00 g/cm3 / 1.025 g/cm3 / 1.84 g/cm3 / 8.92 g/cm3

Specific Gravity

A concept related to density is the specific gravity (or, even more appropriate, relative density) of a material, which is the ratio of the material's density to the density of water. An object with a specific gravity less than 1 will float in water, while a specific gravity greater than 1 means it will sink.

Example - Use the Density to Identify the Material:

An unknown liquid substance has a mass of 18.5 g and occupies a volume of 23.4 mL.

What is the density of the unknown liquid?

If we look up densities of some common substances, we can find that ethyl alcohol, or ethanol, has a density of 790 kg/m3. The liquid may be ethyl alcohol!

BUOYANCY

Buoyancy: theupward force of afluid(liquid or gas)pushing on an object

  • Buoyancy is why you feel lighter in water than on land.
  • Buoyancy is why sea animals can grow to be so large. A blue whale is the largest mammal to have ever lived: up to 100 feet long. The water supports a whale’s body.

Archimedes Principle:

  • Water pushes up on an object immersed in it. The amount ofbuoyancy force it exerts on the object equals the amount of water that is displaced.
  • If the water displaced equals or exceeds the weight of the object it will float.
  • The weight of the wood block is equal to the amount of water displaced, so the block floats.

Example:

An object that weighs 12 lbs is placed in the water. 15 lbs of water is displaced. Does this object sink or float?

Answer:

This object floats. If the amount of liquid that is displaced is more than or equal to the weight of the object, the object will float.

Practice:Use the information in problems 1and 2 to decide if the object is floating or sinking.

  1. You place an object that weighs 63 lbs into fresh water, but it displaces 62.4 lbs of water. Does this object float or sink? Why?
  1. You place the same object as in problem 1 into salt water. It displaces 63 lbs of water. Does this object float or sink? Why?

Now for something a little more complicated:

  1. A 0.5 Kg toy submarine made of steel is able to float in a bathtub. When it’s completely submerged, it displaces 1 Kg of water. What could you do to the toy sub to make it sink to the bottom?
  1. A ping pong ball is dropped down a pipe sticking out of the road. What could you do to get the ping pong ball back? (HINT: Ping pong balls are 0.01g and displace 0.005g of water)