Define 'Buoyant force'. What is the cause of buoyant force? Explain an activity to show how buoyant force changes as the volume of an object immersed in water changes.

Buoyant Force:

Buoyant force, often simply called buoyancy, is the upward force exerted by a fluid (liquid or gas) on an object immersed in that fluid. It is the force that opposes the weight of the object and makes objects seem lighter when submerged in a fluid. The buoyant force always acts in the opposite direction to gravity, which means it pushes an object upward.

Cause of Buoyant Force:

Buoyant force is caused by the difference in pressure between the top and bottom of an object submerged in a fluid. This difference in pressure occurs because the pressure in a fluid increases with depth. As an object is submerged deeper, the pressure on its bottom surface is greater than the pressure on its top surface. The result is an upward force on the object, which is the buoyant force.

Activity to Demonstrate How Buoyant Force Changes with Volume:

To demonstrate how buoyant force changes as the volume of an object immersed in water changes, you can perform the following experiment:

Materials:

A clear container (e.g., a glass or a plastic container)
Water
A small object that can easily float (e.g., a small plastic toy or a cork)
A balance or a simple weighing scale
A ruler or measuring tape
Procedure:

Fill the clear container with water, leaving some space at the top.

Measure the initial weight of the small object you selected. Record this weight.

Gently place the small object into the water and observe whether it floats or sinks. Take note of its behavior.

Now, measure the volume of the small object. You can do this by measuring its length, width, and height and calculating its volume (Volume = Length × Width × Height).

Remove the object from the water and dry it thoroughly.

Repeat steps 2-5 for different volumes of the object. You can do this by cutting or reshaping the object while keeping the material the same. Ensure that you record the weight and volume for each variation.

Observations:

You will notice that as the volume of the object changes, its buoyancy also changes. When the object has a smaller volume, it may sink more easily, and when it has a larger volume, it may float more readily. This demonstrates that the buoyant force acting on the object depends on its volume.

Explanation:

The reason for this behavior is that the buoyant force is directly proportional to the volume of the object displaced by the fluid (in this case, water). When the object has a greater volume, it displaces more water, leading to a larger buoyant force. When it has a smaller volume, it displaces less water, resulting in a smaller buoyant force. This experiment illustrates Archimedes' principle, which states that the buoyant force on an object is equal to the weight of the fluid displaced by the object.