Penny Lab Answer Key - A
7th Grade Environmental Science
Mrs. Krempa
#1. The independent variable in this experiment was the side of the penny.
#2. The dependent variable in this experiment was the number of drops on a penny.
#3. Surface tension is what makes water dome on the penny.
OR…
Water domes on the penny because of surface tension
#4. This lab was a controlled experiment because we only changed one variable which was the side of the
penny. We tried to keep all other variables like water temperature, dropper height etc., the same.
(Other variables could be-year/condition of the penny, dirty/clean penny, design on the penny)
#5. Wallace’s answer… Three trials were taken because if I only did the lab once, I could have made a
mistake that gave me a wrong answer. More trials would let me compare my data and rule out the mistake.
#6. My group fit __ drops on the Heads side of a penny in trial #1. In trial #2 my group fit __ drops.
(Data Table #1). The results don’t match. We had __ more (less?) drops in trial #1. One reasonwhy the results don’t match is drop size. A second reason could be the height the eye dropper was held away from the penny. (other reasons – penny not dry between trials, sponge on a tilt, warm water (not cold), air bubbles, miscounting drops…)
#7. A. My group average for the heads side of the pennywas__ drops. (Data Table #1). The class
averagewas__drops. (Data Table #2). My group had __drops less (more?) than the class.
B. My group average for the tails side of the pennywas __ drops. (Data Table #1). The class
averagewas__ drops. (Data Table #2). My group had __ drops less (more?) than the class.
C. Overall, both my heads results and my tails results were lower than the class by only a little bit (a
lot?). (Graph #2).
Or…
Overall, my heads results were higher (lower?) than the class by a lot (a little?) and my tails results were lower (higher?) than the classby a lot (a little?). (Graph #2).
D. Overall the __ side of the penny held more drops for my group. The class however, had more
drops on the __ side of the penny. Our data did not match the class. Overall there was only a __ drop difference between heads and tails for the class on average. (Data Table #2). I’m surprised! I thought there would be a larger (smaller) difference in the sides. I thought the __side had way more detail and would hold a lot more water than the__ side.
Or…
Overall the __ side of the penny held more drops for my group and the class. (Data Table #2). Our data did match the class. I’m surprised! I thought there would be a larger (smaller) difference in the sides. I thought the __ side had way more detail and would hold a lot more water than the __ side.
#8. The problem of this lab was to see if the heads side or tails side of a penny would hold more drops of water.
We did this lab because we are studying the steps of the scientific method.
#9. During the Penny Lab, we were required to count the maximum number of drops of water each side of a
penny could hold. We placed a dry penny on a piece of damp sponge and used a pipette to drop water on the heads side of the penny until the water spilled over. The results were recorded on a data table. We dried the penny and repeated the trial two more times. We then flipped the penny and repeated the procedure three times on tails side of the penny.
#10. My hypothesis was that the ___ side of a penny would fit more drops of water. My group’s data
supported my hypothesis because the ___ side of the penny had ___ drops and the ___ side of the penny had ___ drops. (Data Table #1). I think the __ side fit more drops because it had more detail (or was cleaner or… whatever you mentioned in your hypothesis!)
Or…
My hypothesis was that the ___ side of a penny would fit more drops of water. My group’s data did not
support my hypothesis because the ___ side of the penny had ___ less drops than the ___ side of the penny (Data Table #1). I think the __ side fit more drops because it had more detail (or was cleaner or… other variables that may have affected drop count!)
#11. Problem:Explanation:
- Drop sizeLarger drops fit less on the penny, small drops = more
2. Miscounting dropsCounting bubbles or missing multiple drops will make your
final count wrong
3. Sponge on slantA slant or tilt to the sponge would make the water spill to
one side easier
Fixes:
1. Use a machine (flowmeter) that makes a specific drop size
2. Count very carefully
3. Make sure sponge is level and not on the paper towel
*Other problems- hot not cold water (surface tension), not drying penny between trials,
air bubbles, not filling pipette all the way, height of pipette…