What your Preschooler will Learn from this Preschool Physics Experiment

Objects that are heavier than water will sink, while objects that are lighter will float.

When you add salt to your water, you make it heavier so objects that sunk before will now float.

What you Need for this Preschool Physics Experiment

Empty plastic jug (An empty gallon milk container would be perfect or a large Tupperware container with a good seal).

Water

Two big bowls

Salt

Objects that won't be damaged if they get wet. Good examples are going to be plastic Lego's, a juice box, a water bottle, plastic toys, and action figures. If you really want to trick your preschooler, find a rock and a piece of bark that's about the same size.

What To Do

Step one: Have your preschooler pick up your empty plastic jug.

Step two: Fill up the jug with water.

Step three: Have your preschooler try to pick it up. Don't let them hurt themselves swinging your jug around or trying to pick it up though. From this they'll learn that water is heavy.

Step four: Fill your two bowls with water.

Step five: In one of your bowls add salt. Stir it to make sure it dissolves completely.

Step six: Have your preschooler drop the objects one by one into the water bowl. If your preschooler is old enough, have them guess which objects will float or sink. Then put the same object into the salt water bowl. Have your preschooler guess whether it will sink or float. Keep notes to make this preschool science experiment even more scientific.

Hi! I'm Theresa Halvorsen, the preschool science and nature writer for Preschoolrock.com. I have twin boys and am blown away by their fascination with preschool science and how the world works around them. I am always looking for fun and simple science activities so preschoolers can learn about science and the natural world. Please contact me with any suggestions, ideas or questions you have about this site.

Helpful Tips for Parents

• Use correct scientific vocabulary from the start: observe, predict, experiment, hypothesis, result, evidence. Children absorb vocabulary in context without explicit teaching.

• Repeat experiments multiple times. Reliability — the same result happening consistently — is a key scientific concept, and repetition gives preschoolers the proof they find satisfying.

• Outdoor science (nature observation, weather tracking, garden study) is as rigorous as lab science and has the added benefit of physical activity and environmental connection.

• Science supplies don't need to be purchased. Vinegar, baking soda, cornstarch, salt, food coloring, and dish soap cover most preschool science experiments adequately.

Frequently Asked Questions

How do I build a child's science confidence when they get frustrated by unexpected results?

"Unexpected" is the word to use rather than "wrong" — in science, results that don't match predictions are the most interesting. "The result was different from what we expected — that means we discovered something! Let's figure out why." This reframe makes the unexpected result a success rather than a failure, because it produced a question worth investigating. Science confidence is built by treating all results as valid data, never as failure.

Are commercial science kits appropriate for preschoolers?

Commercial science kits designed for ages 4+ can be engaging starting points. Look for kits that use simple, safe materials and produce visually dramatic results (crystal growing kits, volcano kits, solar system model kits). Avoid kits with very small parts, complex safety requirements, or expected outcomes that are frustrating when not achieved. The best kits are those that leave children wanting to experiment further beyond the kit's instructions — look for kits with extension activities built in.

Related reading: See also our bubble experiments and our science experiments at home for more ideas on this topic.

🎓 Skills Your Child Will Develop

• 🔬 Scientific Method — Even a simple experiment teaches the predict-test-observe cycle that is the foundation of scientific thinking — and preschoolers who internalize this process approach problems with genuine scientific confidence.
• 🤔 Critical Thinking — Making a prediction, testing it, and explaining the result develops logical reasoning — the ability to move from observation to explanation that underlies all scientific, mathematical, and analytical disciplines.
• ⚖️ Cause & Effect Understanding — Seeing that one action reliably produces a specific result builds the logical framework children use in mathematics, reading (one event causes another in stories), and everyday reasoning.
• 😌 Patience & Delayed Gratification — Experiments with delayed results — growing plants, watching crystals form, tracking weather — teach children to wait for outcomes rather than needing immediate feedback, a skill that predicts academic and life success.

This is a common preschool science experiment, but it's a good one on hot summer days or days when you're trapped in the house due to rain or snow. Finding common household items that float or sink in water is a great way to teach your preschooler about weights. Find out if adding salt to your water changes what objects sink or float.