Floating and Sinking

Are you prepared for some hands-on science at home? Summer is a great time for informal science and now is the time to get ready.

From experience, I recommend that you gather items and put together a box for children to use to explore physical sciences whenever the mood strikes. The items you supply don't have to be big or expensive. but if you have it on hand and gathered together, it won't take a minute to get started.

Here are some tried-and-true suggestions that will be sure to ignite your child's inner investigator. Have multiples of each item, and a set for each child you are working with. (Note:  These suggestions are for ages 3+ and always keep safety in mind.)

1. Paper and scissors - for paper airplanes, helicopters, bridges, drawing designs, recording data, etc., etc.

2. Plastic drinking straws to make into kazoos, atomizers, droppers, bridges, you name it

3. Paper towel tubes to make marble towers, airplanes

4. Manila file folders to make ramps, airplanes, etc.

5. Plastic garbage bags or cloth, bits of yarn or string, and action figures to make parachutes (parachute activity)

6. Wheels to make cars and/or toy cars to roll down ramps (inclined planes)

7. Marbles and small balls for marble towers, study what happens when two objects collide by playing marbles (relationships of mass and force)

8. Balloons to make cars, hover craft, drums, etc. (Suggestions for activities with balloons)

9. Magnets, a variety of kinds plus items to test, such as paper clips of different types, coins, the rocks below (Edit: magnet science activities)

10. Stop watch, watch with second hand, or other timing device

11. Flashlight - important tool for investigating shadows, light, how batteries work, etc.

12. Thermometer- alcohol or electronic/digital (for safety, do not use a mercury-based one)

13. Magnifying lenses to study surfaces of rocks, magnets

14. Prisms to investigate light (we got a very inexpensive crystal pendent that works to separate visible light into rainbows)

15. Aluminum foil - great for building boats or make a Leyden jar to study static electricity

16. Building blocks

17. Ruler - both for measuring and to use as a ramp (inclined plane), support, etc.

18. Toy boats to study buoyancy

19. Modeling clay to study floating and sinking, make fossils

20. Clean tin cans with all sharp edges removed (for tin can science)

21. Tape - all kinds, glue

22. Plastic soda or water bottles to make boats, cover with balloon and place in very warm water

23. Pencils, chop sticks, wooden skewers, dowels and/or craft sticks

24. Spools, pulleys

25. Some cool rocks or pebbles can become loads for cars and boats or be an introduction to geology

Pennies make good weights for the front of file-folder airplanes.

More advanced items to make or buy pre-made:

  • Inexpensive kites (often available in grocery stores for just a dollar or two), or balsa wood, string, tape and paper to make kites
  • Electrical circuit kits (may be available used or at discount stores that sell returned/discontinued items)
  • Inexpensive kitchen scale (garage sales) or materials to make a homemade scale
  • Plastic tubing (an aquarium supply) to learn about siphons, investigate propulsion
  • Make a trebuchet or catapult

If you have any other ideas for items to include for physical science activities, please let us know. Also, if you need further suggestions or instructions, my "engineer" and I would be glad to help.

Stay tuned for suggestions for a chemistry activity box and a biology activity box.


This week our science fun has been inspired by a book that just came out, Planting the Wild Garden by Kathryn O. Galbraith and illustrated by Wendy Anderson Halperin. See Wrapped in Foil blog for a full review.

Planting the Wild Garden is a beautifully illustrated picture book that is a delightful introduction to the ways wild seeds move around (are dispersed).

Plants can't move once they start growing, yet we see plants almost everywhere. How did they get there? Most travel as seeds. Seeds have many different ways to spread and scatter.

In this video from the Life of Plants by David Attenborough we get to see some marvelous footage of the amazing ways seeds move. Note: there is a pop-up ad.

Activity 1. Investigate seed structure and movement through observation.

Here at Growing with Science we have a regular feature called Seed of the Week. Take a look at some of the seeds and guess how they might be transported from place to place. For example, check the Chinese elm seeds (samara) with their tiny wings. Don't they look like they could fly?

Go outside and look for seeds, particularly in the fall. Observe them and try to figure out how their structure helps them get from place to place. Look at them through a hand lens. Toss them in the air. Blow on them. Put the seeds in a puddle. See if they will stick to your sleeve. Think about where you see seeds and how they got there.

Activity 2. Floaters

As you saw in the video, seeds like the sea bean can float from place to place. They don't have to be in a big body of water like the ocean either. A small trickle created by a downpour of rain may be enough to float seeds away.


  • Large bowl, sink, tub or aquarium to fill with water
  • Seeds or fruits to test for ability to float:   coconuts, cranberries, a pinto bean or other dried bean, etc.

Predict what will happen to each item and then test each item. Let the seeds or fruit float as long as possible to show that they might reach land without sinking. You might want to cut open a cranberry to show the seeds inside.  (Remember that cranberries are harvested by floating them in ponds). Does a cut cranberry float?

More advanced activity:

Scientists in Hawaii needed to know how plants arrived on the islands in order to protect native species and prevent introductions of invasive species. A scientist named Henry Guppy placed different seeds in jars of seawater for several months to see how long they could float. Design your own experiment to test which seeds float in your area and investigate how they do it.

Have you ever gone to the beach or the shore of a lake? Look for seeds on the shore that were carried there by water.

Activity 3. Flying Seeds

Most of us have seen seeds flying in the air at one time or another. Dandelions, milkweeds, maple keys and cottonwoods are just a few examples of trees with seeds that ride the wind.

This slide show shows how humans can help cattail seeds disperse.

Dandelion and cattail seeds fly with structures that are like tiny parachutes. If you are interested, try investigating parachutes.

Design an experiment to test how far a dandelion seed can fly. How would you measure it?

Maple keys are so interesting that scientists take high speed movies of them to discover the secrets of their movements. According to this study, the keys produce swirling air like mini-tornadoes while they spin. Here the seed has been dropped in oil to make the whirls easier to see.

Do you see the tiny swirls that form over the end of the "tail" part of the key? Cool!

For more about maple key science, try these links:

Whirling Wonders

NASA Maple Seed Aeronautics

Maple seed science -some of links are broken, but go to Exploring Science and Design with a Maple Seed and click on the words under the pictures to find instructions on how to make the origami and other models to test.

Animals also transport a lot of different kinds of seeds. Whenever an animal, such as a bird, eats a juicy bit of fruit like this pyracantha berry, it ingests the seeds. The seeds end up on the ground later on. Other animals, like squirrels, may bury seeds and forget where they are.

Some seeds, like burdocks, hitch a ride by being sticky or latching on the fur of mammals.

We often think of big animals moving seeds, but tiny ones move a lot of seeds, too. Check for a related post at Wild About Ants for information about ants and seed dispersal.

Finally, by far the coolest are the seeds that pop out of the pods and shoot away. Plants with this kind of dispersal include jewelweed, lupines and Scotch broom. See if you can find a plant that does this and try it out.

And don't forget to pick up a book about seed dispersal, such as Planting the Wild Garden, to learn more and inspire your own investigations.

Reading level: Ages 4-8
Hardcover: 32 pages
Publisher: Peachtree Publishers (April 1, 2011)
ISBN-10: 1561455636
ISBN-13: 978-1561455638


Part of our growing list of Children's Books about Seeds at Science Books for Kids.


Disclosures: The book was provided for review purposes. Also, I am an affiliate for Amazon. If you click through the linked titles or ads and make a purchase, I will receive a small commission at no extra charge to you. Proceeds will be used to maintain this self-hosted blog.


This weekend let's try some experiments with water.

1. pH of the Planet

If you are thinking big, why not participate in the International Year of Chemistry's  Water–A Chemical Solution: A Global Experiment? The organizers are inviting students from around the world to check the pH of local water sources and then report them. Take a look at the website for details. If you want to check out the experiment, look at the .pdf file in the right sidebar labeled Worksheet- PH of Planet, which gives details about the methods.

2. Water Temperature and Density


  • 3 plastic cups
  • 4 zipper top plastic bags
  • sharpie pen to label the bags
  • large container to hold water, or sink or bathtub
  • warm water - about bathtub temperature
  • cold water
  • ice cubes
  • Digital water thermometer (optional)

A. Density and Floating - Do bags filled with warm water versus cold water float the same?

Fill your large container with room temperature water. Place a few ice cubes and some cold water in a zipper top plastic bag. Close the top and let the ice cubes mostly melt, so you have very cold water. Label the bag cold. Fill another zipper top plastic bag with warm water and label it warm. Now place the two bags in the large container. What happens? Do both bags float? Does one bag sink? Why or why not?

B. Playing with Temperature - Does pouring water change its temperature?

Label the plastic cups 1, 2 and 3. Pour some of warm water into the plastic cup labeled 1 (say about 1/2 cup or so) and the same amount into cup 2. Take the temperature of the water in both cups, if you have a digital thermometer. The temperature should be the same in both cups. If it is not, dump the cups and refill with warm water again. Once they are the same, place cup 2 aside to serve as the control.

Now quickly pour the water from cup 1 into cup 3. Pour it back and forth from on cup to the other for about two minutes. End up with all the water back in cup 1.  Now take the temperature of the water in cup 1 and cup 2 again. Are the two temperatures still the same? Why or why not?

C. Does air change density with temperature?

If you still have warm water and cold water in separate containers, try this activity with air. Fill the remaining two zipper lock plastic bags with roughly the same amount of air, but it shouldn't be completely filled. You can blow in the air and then quickly seal it up. Now place one bag in warm water (at least bathtub temperature) and the other in cold water. What happens?

(If you got the right amount of air in, the bag in the warm water should expand noticeably).

If you do these experiments, let me know what you find out. And it have a digital water thermometer, think up some more activities with water. I'd love to hear what you come up with.

Digital thermometers for aquariums are relatively inexpensive.