Physics/Dr. Lankar
Name: ________________ section: ______________: grade: _______
INTRODUCTION -!!!!!READ PLEASE !!!!!U.S.
pennies have been composed of copper and zinc since 1959, but the ratio
of copper to zinc changed over the years because the increase in the
price of copper.
Copper and zinc are both metallic elements and they
share many physical properties. But they have different densities. Pure
copper has a density of 9.0g/mL (or 9g/cm3 because 1 mL = 1 cm3) , while pure zinc has a density of 7.1
g/mL (7.1g/cm3).
But by measuring the density of pennies from different years,
it's possible to track changes in the composition of the penny.
PROBLEM
What are the approximate composition of pennies having various mint dates ?
PROCEDURE
you will need 5 pennies of varying mint date, balance sensitive to 0.01g, 50mL graduated cylinder having 1mL graduations
step1: Record the mint date of each penny in a TABLE 1 below.step2: weigh each penny and record the mass to the nearest 0.01g in TABLE 1. Call the mass mo.step3: Let's find the volume of 1 penny. We are not going to use the amount to displaced water. Get a ruler.
you are going to find the volume of the 5 pennies and then divide by 5 to find the volume of 1 penny.
Stack the 5 pennies. The shape taken by the pennies is a _____________.
What is the formula to find the volume of such shape ? base x height = _________. H is the height and R is the radius.
Use your ruler to find the height in mm. H = _______ mm (the small division on you ruler, 1cm = 10mm)
Now
let's find the surface area of the penny A. Take a penny and very
meticulously find the diameter of the penny. D = _________mm. Find the
radius R = _____mm. (D=2R). So A = _________ mm2 . (use pi on your TI, keep as much decimals possible, round only when you get your final answer. THat's a general rule ).
Now let's find the volume of the 5 pennies = volume of the cylinder = A x H.
V5 pennies = A x H = ______________mm3 (keep as many decimals as possible)
Now you need to convert to mm3 to cm3. 1 cm =10 mm BUT 1 cm3 = _________ mm3 (remember?).
check with your instructor, So V = ____________ cm3 (divide by the factor found just before)
Finally, divide the volume found by 5 to find the volume of 1 penny. V = ________cm3Keep decimals.
TABLE 1
| mint date | mass (g) | density (g/mL) |
| ________ | m=_____ | ________ |
| ________ | ________ | ________ |
| ________ | ________ | ________ |
| ________ | ________ | ________ |
ANALYSIS1) The volume of 1 penny is:
V = _______mL (what you found in step3)
3) Calculate the density of each penny by dividing its mass mo (TABLE1) by the average volume Vo (TABLE2).
density = m/V. Record the computations in TABLE1.
4) Does your group data show any pattern that relates the densities of the pennies to the mint dates ?
You can check other group results.
5) Classify the pennies of each year group examined as mostly copper (density close to 8.95 g/ML)
or as mostly zinc (density close to 7.13g/mL)
6) Why would increases in the price of copper cause the mint to change the composition of penny?
7) extra credits to do on your own: (+5 on next quiz) find the density of nickels (5 cents).
Do you find a density close to the metal
nickel ? do some research on internet to find out what nickels are made of ?