Up-thrust and Archimedes Principle

Sample Video

Title: Exploring Water Resistance and Up-thrust


Water is all around us, and it can be a powerful force that affects objects in unexpected ways. In this reading, we’ll dive into the fascinating concepts of water resistance and upthrust and discover how they play a crucial role in the behavior of objects in water. Water Resistance: Water resistance is the force that opposes the motion of objects as they move through water. Imagine pushing your hand through a pool – you can feel the water pushing back against your hand. This push is water resistance. Just like air resistance in the air, water resistance in water affects how things move.

Factors Affecting Water Resistance:

Several factors influence the amount of water resistance an object experiences:

  1. Size and Shape: Larger objects or those with irregular shapes experience more water resistance.
  2. Speed: Faster-moving objects face greater water resistance than slower ones.

Real-life Examples:

You encounter water resistance in everyday activities:

  • Swimming: When you swim, your body experiences water resistance, making it harder to move quickly through the water.
  • Rowing: The oars of a rowboat push against the water, and water resistance helps propel the boat forward.

Upthrust (Buoyancy):

Upthrust, also known as buoyancy, is the force that pushes objects upward when they are placed in a fluid (like water). Have you ever noticed how a heavy rock sinks in water, but a light rubber duck floats? That’s due to upthrust. It’s the reason why objects seem to weigh less in water.

How Objects Float:

An object floats when the upthrust it experiences is greater than its weight. This happens when the object’s density is less than the density of the fluid it’s in. Submarines use this principle to control their depth – by adjusting their density, they can rise or sink in water.

Archimedes’ Principle:

The ancient Greek scientist Archimedes discovered that the upthrust on an object submerged in a fluid is equal to the weight of the fluid displaced by the object. This principle helps explain why some objects float while others sink.


Understanding water resistance and upthrust is vital in various fields:

  • Ship Design: Engineers design ships to balance weight and buoyancy for safe and efficient sailing.
  • Scuba Diving: Divers use buoyancy control devices to regulate their depth underwater.
  • Swimming: Swimmers use buoyancy to stay afloat and glide through the water.


Water resistance and upthrust are fundamental forces that shape how objects behave in water. From swimming to sailing, these concepts have practical applications that impact our daily lives and scientific advancements. Exploring these principles opens the door to a deeper understanding of the intricate interactions between objects and fluids.


  • Water Resistance: The force that opposes the motion of objects in water.
  • Upthrust (Buoyancy): The force that pushes objects upward in a fluid, counteracting their weight.

Remember, water resistance and upthrust are exciting concepts that show how science helps us comprehend the natural world around us.