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# Biology density

## on May 14, 2011

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Biology density

Biology density

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• ROCKS - pass around
• Hot air balloon - Describe how a hot air balloon works. Defend your argument.
• Sinking vial - make it float
• Beans/ping pong ball; Big jug of water in a pool
• Air bladder when pulled up to quickly
• 250 b.c., the Greek mathematician Archimedes - story

## Biology density Presentation Transcript

• Density
• BW (Bell Work): Why does ice float in water? The Density of water is 1g/cm 3 .  An object will float is the density is less than 1.  An object will sink if its density is greater than 1.
• Description : A fish tank, Coke and Diet Coke are supplied. The Coke sinks while the Diet Coke floats.
• DENSITY
• Depends on:
• Mass
• Volume
• D = m/v (g/cm 3 )
• Mass usually expressed in grams
• Volume usually expressed in cm 3 or liters, etc.
• Density
• Density compares the mass of an object to its volume
• D = mass = g or g
• volume mL cm 3
• Note: 1 mL = 1 cm 3
• What is density?
• A material's density is defined as its mass per unit volume.
• It is a measure of the mass of an object divided by its volume.
• The principle of density was discovered by the Greek scientist Archimedes .
• To calculate the density of an object, take the mass ( m ) and divide by the volume ( v ). This will give you the density in g/cm 3 .
• What would take up more space??? A kilogram of feathers….. or a kilogram of steel? OR
• “ Compactness”
• Density is essentially, a measurement of how tightly matter is crammed together.
• Gases
• How much kinetic energy do the molecules have??
• The greater the kinetic energy
• …… the greater the volume
• …… and the less dense that gas is!!
• Therefore, cold air is more dense than warm air
• Kinetic energy vs. potential energy
Why is cold air denser than hot air?
• Gases
• Real life application…..
• Low pressure weather system means warmer air tends to rise,
• High pressure systems indicate a colder more dense air mass that will…….
• SINK!!!
• Density Large ball – 0.53 g/cm 3 Medium ball – 1.05 g/cm 3 Small ball – 0.82 g/cm 3
• The “bounceability” of a ball depends on its density, not on its mass or on how big the ball is.
• Have you wondered why hot air balloons rise? When the air is heated, it becomes less dense until the balloon's total density is less than that of the atmosphere; A hot air balloon is literally floating on the denser, colder air.
• Do you know why volcanoes erupt? The main reason that magma rises to the surface to erupt at volcanoes is because it is less dense than the rocks that surround it.
• A ship floating on water is a great illustration of the difference between mass and density. A ship must have a density of less than 1.0 g/cm 3 (the density of water), or it will sink. Ships have a large mass, because they are made of steel, but because they have a large volume, their density is less than 1.0 g/cm 3 . If enough mass is added to them such that their density goes above 1.0 g/cm 3 , they will sink.
• You have a rock with a volume of 15cm 3 and a mass of 45 g. What is its density? D = m/v (g/cm 3 )
• What is the mass of a 350 cm 3 sample of pure silicon with a density of 2.336 g/cm 3 ? Mass = density x volume x Mass = 2.336 g/cm 3 x 350 cm 3 Mass = 818 grams D = m/v (g/cm 3 ) m=d x v v=m/d http://serc.carleton.edu/mathyouneed/densitysp.html
• Solving For Mass Original Formula   Multiply both sides by v                                                                      The &quot;v's&quot; cancel out                                                                Isolate for mass                                                                                       m = v x D
• solving For Volume Original Formula                 Multiply both sides by volume                                 m = v x D  Divide both sides by density                          Adjusted formula
• What would happen????
• Mercury density = 13600kg/m 3
• Lead density = 11340kg/m 3
• Lead floats on liquid mercury!
• Solids Ice vs. water…..
• SOLIDS
• Ice is less dense than water (which is why lakes and ponds have a thin layer of ice covering in winter, with water underneath)
• Various rocks, woods, metals have a characteristic density specific to that substance
Wouldn’t you like to have a bunch of THIS dense material?
• Factors affecting Density
• Temperature
• Pressure
• Factors affecting Density
• Dissolved solids – in liquids
• Concentration and kind of substances
• DETERMINING DENSITY
• Regular Shapes – mass, then determine the volume by formula
• EX: cubes, cylinders, spheres, cones, etc.
• Irregular shapes – mass, then measure displacement of a liquid (usually water) by that irregularly shaped object
• The densities for some common substances are: Substance Density (gm/cu.cm) Air 0.0013 Wood (oak) 0.85 Water 1.00 Ice 0.93 Aluminum 2.7 Lead 11.3 Gold 19.3 Ethanol 0.94 Methanol 0.79
• Volume Displacement (water displacement of Irregular shapes
• A solid displaces a matching volume of water when the solid is placed in water.
• 33 mL
• 25 mL
• How are Submarines like fish….
• The swim bladder in bony fish control their relative density in order to rise or dive in the water….buoyancy
• When air is added to the swim bladder, by diffusion through the blood vessels in the bladder walls, the fish becomes less dense overall
• when air is removed fish become more dense
• By changing the volume of air in the bladder, the fish’s density can be made equal to that of the surrounding water at a given depth.
• Home learning
• Make a Seven Layer Density Column
• Seven Layer Density Column
• Find some information about Archimedes' Principle .
• What is Buoyancy?
• Archimedes and the Kings Crown
• Seven Layer Density Column
• Practice Problems
• 1.You want to find the density of a small cube of an unknown material. It measures 1cmx1cmx2cm. It has a mass of 8g
• 2.You discover a gold bar while exploring an old shipwreck. It measures 10cmx5cmx2cm. It has a mass of 1,930g. Find the density.
• 3. A bar of soap measures 8cmx5cmx2cm. Its mass is 90g. Calculate its density. Predict whether this soap will float.
http://www.fordhamprep.org/gcurran/sho/sho/worksheets/worksht27a.htm http://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson27.htm
• Learning Check D1
• Osmium is a very dense metal. What is its
• density in g/cm 3 if 50.00 g of the metal occupies
• a volume of 2.22cm 3 ?
• 1) 2.25 g/cm 3
• 2) 22.5 g/cm 3
• 3) 111 g/cm 3
• Solution
• 2) Placing the mass and volume of the osmium metal into the density setup, we obtain
• D = mass = 50.00 g =
• volume 2.22 cm 3
• = 22.522522 g/cm 3 = 22.5 g/cm 3
• Learning Check
• What is the density (g/cm 3 ) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL?
• 1) 0.2 g/ cm 3 2) 6 g/m 3 3) 252 g/cm 3
• 33 mL
• 25 mL
• Solution
• 2) 6 g/cm 3
• Volume (mL) of water displaced
• = 33 mL - 25 mL = 8 mL
• Volume of metal (cm 3 )
• = 8 mL x 1 cm 3 = 8 cm 3
• 1 mL
• Density of metal =
• mass = 48 g = 6 g/cm 3
• volume 8 cm 3
• Learning Check3
• Which diagram represents the liquid layers in the cylinder?
• (K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL)
• 1) 2) 3)
K K W W W V V V K
• Solution
• (K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL)
• 1)
K W V
• Density as Conversion Factors
• A substance has a density of 3.8 g/mL.
• Density = 3.8 g/mL
• Equality 3.8 g = 1 mL
• Conversion factors.
• 3.8 g and 1 mL
• 1 mL 3.8 g
• Density Connections
• Mass Volume
• kg L
• g mL (cm 3 )
• mg
• Learning Check
• The density of octane, a component of gasoline, is 0.702 g/mL. What is the mass, in kg, of 875 mL of octane?
• 1) 0.614 kg
• 2) 614 kg
• 3) 1.25 kg
• Solution
• 1) 0.614 kg
• Unit plan : mL  g  kg
• Equalities : 1 mL = 0.702 g and 1 kg = 1000 g
• Setup:
• 875 mL x 0.702 g x 1 kg = 0.614 kg
• 1 mL 1000 g
• density metric
• factor factor
• Learning Check
• If blood has a density of 1.05 g/mL, how many liters of blood are donated if 575 g of blood are given?
• 1) 0.548 L
• 2) 1.25 L
• 3) 1.83 L
• Solution
• 1)
• Unit Plan: g mL L
• 575 g x 1 mL x 1 L = 0.548 L
• 1.05 g 1000 mL
• Learning Check
• A group of students collected 125 empty aluminum cans to take to the recycling center. If 21 cans make 1.0 pound of aluminum, how many liters of aluminum (D=2.70 g/cm 3 ) are obtained from the cans?
• 1) 1.0 L 2) 2.0 L 3) 4.0 L
• Solution
• 1) 1.0 L
• 125 cans x 1.0 lb x 454 g x 1 cm 3
• 21 cans 1 lb 2.70 g
• x 1 mL x 1 L = 1.0 L
• 1 cm 3 1000 mL
• Learning Check
• You have 3 metal samples. Which one will displace the greatest volume of water?
• 1 2 3
• Discuss your choice with another student.
25 g Al 2.70 g/mL 45 g of gold 19.3 g/mL 75 g of Lead 11.3 g/mL
• Solution
• 1) 25 g Al x 1 mL = 9.2 mL 2.70 g
25 g Al 2.70 g/mL
• Look at the graduated cylinder. It contains the following liquids. Label the liquids in the graduated cylinder based on the data below. (4 A . B . C D . Liquid Density (g/ml) corn syrup 1.38 ether 1.2 canola oil .93 salt water 1.1
• Put the following steps IN ORDER to demonstrate your understanding of how to find the density of an irregular object.
• 1. _____a. Mass the object on a balance.
• 2. ____ b. Place object in graduated cylinder
• 3. _____c. Using the formula for density, calculate the density of
• the object
• 4. _____d. Subtract initial volume from the volume of the object +
• water
• 5. _____e. Fill graduated cylinder with water above the size of the
• object
• 6. _____f. Include final units for mass and volume in final answer
• 7. _____g. Record initial volume in milliliters
• 8. _____h. Record mass in grams
• 9. _____i. Record volume of object only in milliliters
• 10. _____j. Record volume of object + water in milliliters
• RESOURCES
• http://www.middleschoolscience.com/dietcoke.htm (density Demo)
• http://www.fordhamprep.org/gcurran/sho/sho/labs/densitylab.htm http://www.edinformatics.com/math_science/mvd_quiz.htm (MASS, VOLUME)
• http://www.syvum.com/cgi/online/serve.cgi/members/gillilandd/quizzes/density.tdf (density problems)