How many drops of water fit on a penny?
- 👶 Small parts
- 🚫 Not food
- 💧 Water
- 🧼 Wash your hands after
My hypothesis
If I change what is in the water, then how many drops fit on the penny before it spills over will ______, because ______.
You fill in the blanks. Think about how water drops hold together, and what soap does to that. A guess is a good because: the test finds out.
Change, measure, keep the same
CHANGE
what is in the water: Plain water, Soapy water, Salty water
MEASURE
how many drops fit on the penny before it spills over, in drops
KEEP THE SAME
- the same penny, dried between tries
- the same dropper, squeezed gently
- the penny lying flat, heads up
- the same slow, steady drips
Scientists call the thing you change the independent variable and the thing you measure the dependent variable. The things you keep the same are the controls: if one of them changed too, you wouldn't know which change made the difference. Try each of the 3 levels 5 times.
What you need
- Pennies: 1
- An eyedropper or a medicine dropper
- Water from the tap
- Dish soap
- Salt
- Clear plastic cups, all the same size: 3
- A measuring cup
- Measuring spoons
- A spoon
- Small plates or saucers, all the same: 1
- Paper towels
- Masking tape, to mark lines
Steps
- Pour a quarter cup of tap water into each of three clear cups.
- Stir one drop of dish soap into the second cup, and one teaspoon of salt into the third until it disappears.
- Label the cups plain, soapy and salty.
- Lay a dry penny flat on a plate, heads up.
- Squeeze out one drop at a time onto the penny, and count out loud.
- Stop when water first spills over the edge. Write down the drops you counted before it spilled.
- Dry the penny with a paper towel, and rinse the dropper in clean water between kinds.
- Do five tries with each kind of water.
- Fill in your table, find the mean for each kind, and draw a bar graph.
Every step is one you can do yourself, with a grown-up nearby. Write each number down straight away, in the table below, so nothing is lost.
Your results table
Name ______________________ Fair day ____________
Question: How many drops of water fit on a penny?
I changed: Water I measured: how many drops fit on the penny before it spills over (drops)
| Water | Try 1 (drops) | Try 2 (drops) | Try 3 (drops) | Try 4 (drops) | Try 5 (drops) | Mean |
|---|---|---|---|---|---|---|
| Plain water | ||||||
| Soapy water | ||||||
| Salty water |
MY GRAPH (a bar graph: water along the bottom, drops up the side)
What I noticed: ______________________________________________
From 4th grade, add the tries for each level and divide by how many there were: that's the mean, and it goes in the last column. Then draw a bar graph, one bar for each thing you tried.
Name ______________________ Fair day ____________
Question: How many drops of water fit on a penny?
If I change what is in the water, then how many drops fit on the penny before it spills over will ________________, because _____________________________________________
| I CHANGE | I MEASURE | I KEEP THE SAME |
|---|---|---|
| Water: Plain water, Soapy water, Salty water | how many drops fit on the penny before it spills over (drops) |
|
What I think will happen, in my own words:
Name ______________________ Fair day ____________
Question: How many drops of water fit on a penny?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: How many drops of water fit on a penny?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: How many drops of water fit on a penny?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: How many drops of water fit on a penny?
My hypothesis was ☐ right ☐ partly right ☐ not right.
I know because my numbers show:
What surprised me, or what might have gone wrong (7th and up):
Next time I would test:
Idea: Change a second thing: use 1, 2 and 4 drops of dish soap in the cup, and graph the drops that fit against the soap.
Why it works
Water drops hold together because water's tiny bits pull on each other, which makes its surface act like a stretchy skin. On a penny that skin lets the water pile up into a dome that stands higher than the penny's edge. Soap weakens the pull, so a soapy dome spills sooner and fewer drops usually fit.
Going further (7th and up): Change a second thing: use 1, 2 and 4 drops of dish soap in the cup, and graph the drops that fit against the soap.
Board layout
- ❓ Question (10 × 8 in): How many drops of water fit on a penny?
- 💭 Hypothesis (10 × 9 in): If I change what is in the water, then how many drops fit on the penny before it spills over will ______, because ______.
- 🧺 Materials (10 × 12 in): 12 things: see your list.
- 🪜 Steps (22 × 9 in): 9 steps, three tries at each level.
- 📊 Results (22 × 16 in): Your table (Water down the side, tries across) and your bar graph.
- ✅ Conclusion (10 × 14 in): My hypothesis was right / partly right / not right. I know because…
Materials to list: Pennies; An eyedropper or a medicine dropper; Water from the tap; Dish soap; Salt; Clear plastic cups, all the same size; A measuring cup; Measuring spoons; A spoon; Small plates or saucers, all the same; Paper towels; Masking tape, to mark lines.
Bring photos or drawings of your test. Nothing wet, hot, powered or alive on the table.
This project at your grade
| 1st–3rd grade | Tries: three at each level (one is fine at a first fair). The table: levels and tries, numbers or pictures. The graph: a picture, or a simple bar graph. The conclusion: what happened, in their words. |
|---|---|
| 4th–6th grade | Tries: three at each level. The table: units in the header and a mean column. The graph: a bar graph, or a line for a number that grows. The conclusion: right, partly or not, and the numbers that show it. |
| 7th grade and up | Tries: three or more at each level. The table: a mean for every level of both tests. The graph: a graph with two lines or two sets of bars. The conclusion: the numbers, what might have gone wrong, and a next question. Second variable: use 1, 2 and 4 drops of dish soap in the cup, and graph the drops that fit against the soap. |
From 4th grade up, the table gets a mean column. See every project for 2nd grade, or print a blank results table.
What a judge will ask
- What did you change, and what did you measure? I changed what is in the water and measured how many drops fit on the penny before it spills over, in drops.
- What did you keep the same, and why does that matter? I kept the same penny, dried between tries and the same dropper, squeezed gently the same, so the only difference was what is in the water.
- How many times did you test it? 5 times at each of my 3 levels.
- If you did it again, what would you change or test next? I'd use 1, 2 and 4 drops of dish soap in the cup, and graph the drops that fit against the soap.
Make it yours
Keep this project on this device and Peabody counts down to your fair day, with a plan for each day. Nothing is sent anywhere.
Try next
👨👩👧 For grown-ups and teachers: how much to help, the safety rules, and running a school fair. Science fair v0.16.1 · Checked .