Have you ever thrown sticks into a pond or played with toys in the bathtub? If you have, you might have noticed that some things sink to the bottom while others float on top. But why does this happen? Let’s find out together!
Hi there! My name is Webb, and this is my sister, Bill. We live in a pond, so we see lots of things that sink and float. Today, we’re going to do an experiment to learn more about it!
First, we need a big container of water. We’ll fill it about three-quarters full. Then, we’ll find some objects to test. Remember, if you want to try this at home, ask an adult before putting anything in the water!
Here’s what we found: a penny, a stick, a metal spoon, and a plastic spoon. Let’s guess if each one will sink or float before we test them.
Let’s start with the stick. Bill and Webb think it will float because they’ve seen sticks floating in the pond before. And guess what? It floats!
Next, we have the metal spoon. Both Bill and Webb think it will sink, and they’re right—it sinks!
Now, let’s try the plastic spoon. It looks like the metal spoon, so Bill and Webb think it might sink too. But surprise! It floats!
Finally, we have the penny. It feels like the metal spoon, so they think it will sink. And it does!
Let’s look at our results. The metal spoon and the penny sank, while the plastic spoon and the stick floated. What do the floating and sinking objects have in common?
It turns out, the answer is density! Everything is made of tiny particles we can’t see. Density is about how close these particles are to each other.
Imagine particles are like marbles. If the marbles are close together, the object is dense, like the metal spoon. If they’re far apart, the object is less dense, like the plastic spoon.
Water also has density. If something is more dense than water, it sinks. If it’s less dense, it floats. That’s why the metal spoon and penny sank, and the stick and plastic spoon floated.
Now you know why some things sink and others float. It all depends on density! Try this experiment at home and see what you discover. Let us know how it goes!
Thanks for learning with us, and see you next time!
Density Detective: Go on a treasure hunt around your house to find different objects to test in water. Gather items like a rubber ball, a small toy, a coin, and a piece of fruit. Before testing, make a prediction about whether each item will sink or float. Then, test them in a bowl of water and see if your predictions were correct. Discuss with an adult why each item behaved the way it did based on what you learned about density.
Float Your Boat: Use modeling clay or aluminum foil to create a small boat. Try to make it float in a bowl of water. Once it floats, see how many small coins or pebbles your boat can hold before it sinks. Experiment with different shapes and designs to see which one holds the most weight. Talk about how the shape of the boat affects its ability to float and how this relates to density.
Question Time: Think about these questions and discuss them with a friend or family member: Why do you think big ships made of metal can float? How do fish and other animals in the water use the concept of density to help them swim? Can you think of any other examples in nature where density plays a role in whether something sinks or floats?
