This sink or float experiment is super simple, but it’s always a hit with little ones. It’s perfect for teaching “thinking like a scientist” skills: making predictions, testing ideas, observing, and recording data, all in a fun, hands-on way.
Materials needed
- Small tub of water
- A place where it’s OK to get wet (outside, or on a towel on the kitchen floor)
- A variety of toys and household objects that can be submerged — some that sink and some that float. Include a few that are about the same size but have different densities, like a tennis ball and a rock.
- Paper
- Pencil
Instructions:
- Set the stage: Tell your child you’re going to make predictions (guesses) about whether each object will sink or float, and then test those predictions — just like scientists do.
- Make two charts:
- Chart 1: “Predictions” (guesses)
- Chart 2: “Results”
- Under each title, make two columns labeled “Sink” and “Float.” Write the names of your objects down the side. If your child prefers, they can draw pictures of the objects.
- Test each object:
- Have your child hold the first object. Ask if they think it will sink or float. Record their guess with a checkmark or “X” in the “Predictions” chart.
- Let them place the object in the water and watch closely.
- Record what actually happened in the “Results” chart.
- Repeat: Continue with the rest of the objects, encouraging your child to record their guesses and results themselves. Remind them not to skip making predictions before testing!
Teaching moments
- Embrace mistakes: Explain that making an incorrect guess is not a bad thing (especially if your child is discouraged when this happens). Tell them how scientists love to make incorrect guesses because it helps them get closer to the correct answers. Tell them that they are being a scientist!
- Count the surprises: Look at the results together. How many predictions were correct? How many “surprises” did they find?
- Introduce buoyancy: If your child wonders why some objects float and others sink, talk about how it’s not just weight but density that matters. Heavy things like ships can float because of the way they push water aside (displace it).
Why kids love this experiment
This activity blends play and learning, giving preschoolers the excitement of splashing in water while also developing early STEM skills. They’ll practice prediction, observation, recording, and reasoning, and they might start seeing the world with a little more curiosity.