Are Some Fruits and Vegetables Denser than Others?
Talk It Over
Why do some things float and other things sink? Ships that weigh tons float, so the difference can't depend on weight alone. The volume of the object, or how much space it takes up, makes a difference, too.
- Fruits and vegetables for testing (for example, potato, carrot, onion, kiwi, apple, orange, or others of your choice)
- Kitchen scale that weighs in grams in milliliters
- Jar big enough to put the fruits and vegetables into
- Pan that the jar can sit in
- Measuring cup that measures volume in milliliters
- Weigh the food. Record the weight in grams.
- Set the jar in the pan. Fill the jar with water to the brim, but don't let it run over.
- Carefully put the food into the water. Record whether it floats or sinks.
- If the food sinks, water will spill from the jar into the pan. If the food floats, push it down completely under the water with the point of the pencil so water spills out.
- When water stops spilling over the top of the jar, remove the jar from the pan. Pour the water from the pan into the measuring cup. Measure and record the amount of water in milliliters.This equals the volume of the fruit or vegetable.
- The density of the food is its weight in grams divided by its volume in milliliters.Use the calculator to find the density of each fruit and vegetable you test. For example,if the weight of an orange is 200 grams and its volume is 220 milliliters, its density is 200 g ÷ 220 ml = 0.9 g/ml.
- Repeat steps 1–6 for each food you want to test. Dry the pan and the measuring cup with the towel between the tests.
Wipe up spilled water from the floor immediately to prevent falls.
Put different fruits and vegetables in water. Observe and record whether they sink or float. Weigh the foods to show that some heavy ones float, while some lighter ones sink.
The density of pure water is 1 g/ml. (That's because 1 gram of water has a volume of 1 milliliter. 1 g ÷ 1 ml = 1 g/ml.) Use the procedure defined in "Go" to measure the density of objects around the house. Use your data to discover the mathematical rule that predicts whether objects sink or float. (Hint: How do the densities of objects that float and sink compare to the density of water?) Use the rule to explain why huge steel ships float, but tiny steel nails sink.
Show Your Results
Make a data table like this for "Go Easy":
|Food Tested||Sink/Float (Tell Which)||Weight in grams|
For "Go," arrange the foods in a data table from least to greatest density. Display samples of the foods you tested. Show some that sink in water and some that float. Display the tools you used to make your measurements.
|Food Tested||Weight (in Grams)||Volume (in Milliliters)||Density# (Weight ÷ Volume)||Sink or Float (Tell Which)|
|Pear . . .and so on|
# Calculated value
For "Go Far," make a table like the "Go" table and display the objects that you measured for density. On a poster, show the mathematical rule that explains floating and sinking and tell why some very heavy objects can float while some very light ones sink. If you want to expand your project even further, try using density measurements to explain why an unpeeled orange floats, but a peeled orange sinks.
Tips and Tricks
Kitchen scales and measuring cups work fine for this project, but if you can borrow a metric balance and graduated cylinder from the school laboratory, you'll get betternumbers.
Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state’s handbook of Science Safety.