Etiket Arşivleri: DENSITY

Properties of Liquids: Density and Buoyancy

Properties of Liquids: Density and Buoyancy

Definitions

Density:

The mass per unit volume of a material.

Density

The symbol for density is usually D and has units of g/cm3.

Density is a physical property of a material.

Often, a material’s density is used to identify it.

Solids, liquids, gases, and other phases of matter all have densities.

Solids are most dense, liquids next dense, and gases least dense

MOST of the time, density is inversely related to temperature.

Calculating Densities

A Density Problem:

You found this ring on the track at your school. You wondered what it was made of.

You calculated it’s density to be approximately 7.9 g/cm3.

What is it made of?

Forces

  Newton’s Laws:

1.) The law of inertia: An object in motion stay in motion until it is acted upon. Or, an object at rest stays at rest until acted upon.

2.) F = m*a

3.) When two bodies interact by a force, the force on the first body is equal in magnitude and opposite in direction to the force on the second body.

Archimedes’ Principle

The buoyant force exerted on an object submersed in a fluid is equal to the weight of the fluid displaced.

But what does that mean?!?

Fb = D*V*g

Fb : Buoyant force

V  : Volume of fluid displaced

D  : Density of fluid

g  : Acceleration due to gravity

Why does it float?

For an object to float:

Wobject  =  Fbuoyant

Buoyancy Calculations

The polar bear on ice:

A 500 kg polar bear sees a slab of ice floating by and tries to hop on. The ice has a volume of 4 m3 and a density of .92 g/cm3. Seawater has a density of 1.035 g/cm3. Does the polar bear float away happily?

Activity

You will determine the density of a liquid and use that density to identify the liquid.

Good luck!

Questions?


Mass, Volume & Density

Mass
Measurement of the amount of matter
(or stuff) in an object
Measured in grams (g)
Volume
Measurement of the amount of space an object takes up
Measured in milliliters (ml) or cm3
Which do you think would have the greater volume? The greater mass? Why?

Which one is more dense?
Demonstration: People in a square

How about this: Which square is more dense?
Which one is more dense?
Now which one is more dense?
To find the density
3- Divide
Density = Mass g
Volume c³

Let’s try some density problems together Work on these problems with your neighbor
1 Frank has a paper clip. It has a mass of 9g and a volume of 3cm3. What is its density?

2. Frank also has an eraser. It has a mass of 3g, and a volume of 1cm3. What is its density?

3. Jack has a rock. The rock has a mass of 6g and a volume of 3cm3. What is the density of the rock?

4. Jill has a gel pen. The gel pen has a mass of 8g and a volume of 2cm3. What is the density of the rock?
Change Mass AND Keep Volume Same
Increase the mass  increase density
Decrease the mass  decrease in density
Which container has more density?

A B
Change Volume AND Keep Mass Same
Increase the volume  decrease density
Decrease the volume  increase density
Which container has more density?

A B
In your notebook illustrate the answer to the following question: What 2 ways will INCREASE density?
What 2 ways will INCREASE density?
Liquid Layers
If you pour together liquids that don’t mix and have different densities, they will form liquid layers.
The liquid with the highest density will be on the bottom.
The liquid with the lowest density will be on the top.
Objects or substances with MORE density will sink below objects or substances with LESS density
Which do you think is MORE dense,
Water or Oil???

Water, Oil…and a Superball
The oil is less dense than the water, so it’s on top. The superball is less dense than water, but more dense than oil, so it sinks to the bottom of the oil layer, yet floats on the top of the water layer.

The density of five liquids are measured as follows:
Liquid 1: 1.0 g/mL
Liquid 2: 1.38 g/mL
Liquid 3: 0.77 g/mL
Liquid 4: 2.95 g/mL
Liquid 5: 0.056 g/mL

Draw a picture of all 5 liquids in a test tube how they would layer according to density
Liquid Layers
Check out this picture. Which layer has the highest density?
Which layer has the lowest density?
Imagine that the liquids have the following densities:
10g/cm3. 3g/cm3.
6g/cm3. 5g/cm3.
Which number would go with which layer?
Liquid Layers – Try with your neighbor
Which liquid has the highest density?
Which liquid has the lowest density?
Which liquid has the middle density?
Liquid Layers Try on your own!
Imagine that the liquids on the right have the following densities:
15g/cm3 10g/cm3
3g/cm3 9g/cm3
7g/cm3 12g/cm3
Match the colors to the correct densities.
Review
What is the formula for density?
What happens if you pour together liquids that have different densities?
Will the liquid on the top have the highest or lowest density?
Will the liquid on the bottom have the highest or lowest density?
Super Scientist Question of the Day
Jake has a book, a ruler, and a balance.
How can Jake find the density of the book with the tools he has?

http://sunhousescience.blogspot.com/
http://www.icoachmath.com/Sitemap/images/Cuboid1.jpg
http://tinfoiler.com/wp-content/uploads/2010/05/Oil-and-water.jpg
http://www.stevespangler.com/stevespangler/uploads/2008/07/seven-layer-column.png

Laboratory‎ > ‎Density of Liquids

ANSWERS:

1. Density is the ratio of the mass of a substance or object to its volume. At any given temperature, the ratio of mass to volume is characteristic for a given substance.

a) The density of the liquids does not effect on the pressure. But the temperature effects the density of liquids. An increase in temperature produces an increase in the kinetic energy available to the molecules, enabling them overcome the intermolecular forces to a greater extent and move further apart. This behavior decreases the density of the liquid.

b) Liquids cannot be compressed easily. So if you wanna observe changing density of a liquid you need a great pressure.

c) The pressure of the gas in increased by decreasing the volume the gas may occupy (thereby producing more molecule-wall collisions and thus a higher pressure). The molecules are forced to occupy a much smaller space, producing a higher density.

Best Fluid Mechanics Summary

DENSITY, SPECIFIC VOLUME, SPECIFIC WEIGHT, AND SPECIFIC GRAVITY

SURFACE TENSION AND CAPILLARITY

THE PRESSURE FIELD IN A STATIC LIQUID

STRESS, PRESSURE, AND VISCOSITY

FORCES ON SUBMERGED SURFACES AND THE

CENTER OF PRESSURE

ONE-DIMENSIONAL FLOWS

FLOW OF A REAL FLUID

ARCHIMEDES PRINCIPLE AND BUOYANCY

STEADY, INCOMPRESSIBLE FLOW IN CONDUITS AND PIPES

Minor Losses in Pipe Fittings, Contractions, and

Expansions