Honors Physical Science

Mr. Mahlum

Daring to Discover Density

Background Information:

 

Density is a physical property and can be used to identify and unknown substance.  Density is defined as the ratio of mass to volume.  If you measure mass in grams and volume in cm3, the units fro density are g/cm3.  However, volume can also be measured in milliliters (mL), so density can be measured in both g/cm3 and g/mL.

 

Over 2000 years ago King Hieron of Syracuse suspected that a jeweler made his gold crown of gold and another cheaper metal.  Therefore, the crown was not pure gold.  Although the king could measure the mass of the crown, its intricate design prevented measurement of volume.  Thus the king could not know if the crown was gold or not.

 

King Hieron hired Archimedes, a Greek mathematician, physicist and engineer to sole his dilemma.  Archimedes knows that in order to solve th4e problem, he had to calculate the density of the crown and match it to the density of pure gold.

 

While taking a bath, Archimedes noticed the water level rise as he lowered himself into the tub and know he had the solution.  He could find the volume of the crown by measuring how much water it moved, or displaced.  He was so exited about his great discover that he ran through the streets of Syracuse naked shouting “Eureka!!” which is Greek for “I have found it.”

 

Using the mass and volume of the crown, he calculated the density of the crown.  The crown was indeed a fake.  Archimedes was a hero.

 

In this lab, you will use water displacement in order to measure the volume and ultimately identify 3 unknown metals.

 

 

Materials:

 

Electronic balance

Several bags of metal cylinders or other shapes (4 or 5 pieces to a bag)

Graduated cylinder

Water

Beaker

 

Procedure:

  1. Obtain the materials listed above.

 

  1. Carefully and accurately measure the mass of each “shinny” metal sample.  Record these values in the data table.
  2. Fill a graduated cylinder with some water.  Record the exact level of the water in the data table as initial volume of water.  This value will be recorded to the nearest decimal point!!!!

 

  1. Carefully slide the first metal sample into the graduated cylinder.  The sample must be completely submerged in the water.  If it is not repeat step 3 with a greater amount of water.  Measure the new level of the water.  Record the exact level of the water in the data table as final volume of water.  This value will be recorded to the nearest decimal point!!!!

 

  1. Calculate the volume of the metal by subtracting the initial level of water fro the final level of water.

 

Volume of metal = Final level of water – Initial level of water

 

  1. Repeat steps 2-5 for the “dull” metal and the “fishing sinkers”

 

Graphs:

  1. Make a graph of Mass vs. Volume for the metals.  Mass will be on the y-axis, and volume will be graphed on the x-axis.  Plot all three data tables on ONE GRAPH!!

 

  1. Plot data points for each o f the metals measured using a different color for each type of metal.  Make a legend to demonstrate how the color corresponds to the metal sample.

 

  1. Draw best fit lines for each of the metals on your graph use different colors

 

  1. Calculate the slope of each line. The equation for slope is:

 

Slope = (y2 – y1) / (x2 – x1)

 

  1. Compare the observed density value with the accepted values provided by your instructor.  Calculate the experimental error for each metal

 

Exp. Error  = ((Observed value – Accepted value) / (Accepted value)) * 100

 

Questions:

  1. Based on the story about Archimedes in the introduction to this lab how did Archimedes test to see if the kings’ crown was gold?
  2. List the following substances in order from the lowest density to the highest.  Lead pipe, water, pine 2 x 4 board, Styrofoam packing peanuts, and aluminum foil.
  3. List one area of engineering where the density of a material might be important.  Be specific and explain your answer.