Floating and Sinking

In the last unit, students used propeller cars to explore the relationship between forces and motion. In this unit, students continue to explore vehicles with a focus on boats and specifically the science phenomena of properties that cause objects such as boats to float or sink. This page showcases parts of each element of the first lesson in this unit.

Science Background for Teachers:

The science background gives teachers in-depth information about the science phenomena being studied by students. In this unit, students explore density by exploring what properties of objects make them float or sink.

Density is the amount of matter packed in a certain amount of space. In other words, it is a measure of the amount of mass in a given volume.

Volume is the measure of how much space a substance takes up. The more tightly packed the molecules of an object are, the denser they are. This is because they have more mass in a given volume than materials that are less dense.

Objects float when they are less dense than the fluid they are in. For example, salt water produces a greater buoyant force than fresh water because salt water is much denser than freshwater. This is why objects float more easily in salt water than in fresh water, and why a bowling ball floats in the Dead Sea.

The shape of the object also affects its buoyancy because the more surface area an object has, the more water it displaces and the more the water pushes back. This helps the object float.

Science Lesson: Comparing Floating and Sinking

In this lesson, students investigate how objects float or sink depending on their density and then investigate how changing the shape of an object can affect whether it floats or sinks.

Science Big Ideas

• Materials have different properties and certain properties can make a material useful for a particular function.
• Density is important for determining whether an object will float or sink.
• The shape of an object matters in determining whether it floats or sinks.

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Science Essential Questions

• What properties of matter determine whether an object floats or sinks?
• Why is density a property of matter?
• Why would a bowling ball sink in fresh water but a beach ball float in the same water?
• How does changing the shape of an object affect whether it floats or sinks in water?

Common Science Misconceptions

Misconception: All big objects sink, while little objects float.
Fact: The most important factor in whether an object floats or sinks is its density. An object’s density is determined by the materials that make it up and its volume.
Misconception: The shape of a boat is unrelated to how well it can stay afloat.
Fact: A boat’s shape plays a major role in how buoyant the boat will be. Other factors that influence buoyancy include size and the materials of the boat.

Science Vocabulary

Density : a property of matter; the amount of matter packed in a certain amount of space

Float : to stay above the surface of water or another fluid such as air

Sink :  to drop down in water or another fluid such as air

Lexile(R) Certified Non-Fiction Science Reading (Excerpt)

The Dead Sea is a body of water. People come from all over the world to visit it. It is famous because it is very salty. It is much saltier than the ocean.

People float easily in the Dead Sea. To float means to stay above the surface of water or another fluid such as air.

Density and Floating

Objects float when they are less dense than the fluid they are in. Density is a property of matter. It is the amount of matter packed in a certain amount of space.

The particles of a dense object are packed tightly together. The particles of a less dense object have more space around them.

Salt water is denser than fresh water. There are more particles in a cup of salt water than there are in a cup of fresh water. Both cups of water have the same amount of water. But fresh water doesn’t have many particles of salt.

Hands-on Science Activity

For the hands-on activity in this lesson, students investigate how objects float or sink depending on their density and then investigate how changing the shape of an object can affect whether it floats or sinks. In the first part of the investigation, students analyze the properties of different objects and then drop the objects into a water-filled test container to see if they float. In the second part of the investigation, students mold a clay ball into a shape that can float in the water. Students use the data they gathered from both parts of the investigation to construct an explanation about how the properties of an object affect whether it floats or sinks in water.

Science Assessments

KnowAtom incorporates formative and summative assessments designed to make students thinking visible for deeper student-centered learning.

• Vocabulary Check
• Lab Checkpoints
• Concept Check Assessment
• Concept Map Assessment
• And More...

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