What Is Upthrust (Buoyancy)?

Are you looking for an easy way to teach your child about upthrust (buoyancy)? We’ve put together a set of free materials that parents and teachers can use right away. In this lesson, your child will dive into the fascinating world of fluid mechanics.

We’ll explore how water pushes upward on objects to help them float. Explore science in a more engaging way with captivating 3D videos and interactive quizzes. Download our app to get started!

What You Will Learn From This Lesson

What is the upthrust (buoyancy)?

In the field of physics, any object placed in a liquid experiences an upward force known as upthrust or buoyancy. This force acts in the opposite direction of gravity by pushing objects toward the surface.

Whether an object is fully submerged or just floating on the top, this invisible upward interaction is constantly at work.

The strength of this upward force is directly related to the volume of the liquid that the object pushes out of its way. Scientists observe that the more liquid an object displaces, the greater the upthrust it will experience.

This explains why large structures like ships can stay afloat even if they are very heavy.

What influence buoyant forces?

The magnitude of upthrust (buoyancy) is also affected by the specific type of liquid involved in the interaction. For example, a person diving in the ocean experiences a much greater upward force than someone swimming in a freshwater lake.

This occurs because ocean water contains a high amount of salt which increases the density and the resulting upward push on the body.

Practical applications of these principles are found in many safety and recreational tools we use today. Consider the following examples:

• Kayaks rely on upthrust to carry passengers across rivers and lakes.
• Fishing floats use buoyancy to stay on the surface and signal when a fish takes the bait.
• Lifebuoys increase the total upthrust acting on a person to make water activities much safer.

Fun Fact

• Saltwater in the ocean pushes up much harder than the freshwater in a pond.
• The more water an object pushes aside the more buoyancy it will receive.
• Fishing floats are tiny experts at using upthrust to stay on top of the water.
• Density is like a game of musical chairs; a jar of stones is much more “densely packed” than a jar of fluffy marshmallows!
• Inner Weights at the bottom of the hydrometer’s glass bulb act like an anchor, keeping the hydrometer standing perfectly straight up while it takes its measurement.

Vocabulary

• Upthrust (Buoyancy): An upward force exerted by a liquid that pushes objects toward the surface, acting in the opposite direction of gravity.
• Fluid Mechanics: The field of physics that explores the behavior of liquids and the invisible forces, such as upthrust, that govern objects in wet environments.
• Displaced Liquid Volume: The amount of liquid that an object pushes out of its way; the more liquid displaced, the greater the upthrust the object experiences.
• Density: A measurement of how “densely packed” a substance is, similar to a jar of stones compared to a jar of fluffy marshmallows; higher density, such as in saltwater, increases the upward push.
• Saltwater: A type of liquid containing high amounts of salt that increases the magnitude of upthrust compared to freshwater.
• Hydrometer: A glass tool used for measurements that features inner weights at the bottom to keep it standing perfectly straight while in a liquid.