Pressure in liquids | Fluids | Physics | Khan Academy

Summary

This educational video delves into the concept of pressure within liquids, using the analogy of water balloons to illustrate how pressure increases with depth. It explains that unlike solids, liquids exert pressure in all directions due to their fluidity, which is why water shoots out with varying speeds from differently positioned holes in a bottle. The video also connects this principle to real-world applications, such as the design of submarines and dams, emphasizing the importance of understanding liquid pressure for both scientific experiments and engineering structures.

Takeaways

• 💧 **Pressure in Liquids**: Water and other liquids exert pressure in all directions due to their tendency to flow.
• 🚰 **Vertical Pressure Increase**: The pressure in a liquid increases with depth because of the increasing weight of the liquid above.
• 🔄 **Horizontal Pressure Consistency**: At a given depth, the pressure in a liquid is the same in all horizontal directions.
• 💭 **Conceptualizing Liquids**: Imagining liquids as tiny cubes stacked on top of each other helps to visualize how pressure is distributed.
• 🎈 **Balancing Forces**: Just like a stack of water balloons, the pressure at any point in a liquid is the result of forces balancing out.
• 📉 **Pressure Calculation**: Pressure is calculated as force divided by the area over which that force is applied.
• 🌐 **Deformation and Flow**: Liquids, unlike solids, can deform and flow, which means they exert pressure on the walls of their containers.
• 🏊 **Submarines and Pressure**: Submarines can get crushed at great depths due to the immense pressure exerted by the water.
• 💦 **Water Bottle Experiment**: The water bottle experiment demonstrates how water at different depths exits the bottle at different speeds due to varying pressure.
• 🏭 **Practical Application**: The principle of increasing pressure with depth is used in the construction of dams, which have wider bases to withstand this pressure.

Q & A

What happens when you punch two holes in a water bottle, one at the top and one at the bottom?

Water squirts out from both holes, but the water at the bottom comes out with a much higher speed and falls farther away compared to the water at the top.

Why does the water at the bottom hole come out with more speed than the water at the top hole?

The water at the bottom hole comes out with more speed because it is under greater pressure due to the weight of the water above it, which increases with depth.

How does the pressure inside a liquid relate to its depth?

The pressure inside a liquid increases with depth because the liquid at lower depths has to support the weight of the liquid above it.

What is the relationship between pressure and the forces acting on an object submerged in a liquid?

The pressure on an object submerged in a liquid is directly related to the force acting on it per unit area, which increases with the depth of the object in the liquid.

Why do submarines get crushed when they dive too deep?

Submarines get crushed when they dive too deep because the pressure of the water increases with depth, and at great depths, the force per unit area on the submarine's hull becomes too high for the metal to withstand.

What is the formula to calculate pressure?

Pressure is calculated using the formula pressure = force divided by area.

How does the pressure in a liquid compare horizontally versus vertically?

Horizontally, the pressure in a liquid remains the same at any given depth, whereas vertically, the pressure increases with depth.

Why do liquids push on the walls of their container?

Liquids push on the walls of their container because they can flow and deform, which allows them to exert pressure in all directions, including horizontally.

How does the concept of pressure in liquids relate to the construction of dams?

The concept of pressure in liquids is applied in the construction of dams by making the base wider to withstand the increased pressure exerted by water at greater depths.

What is the difference between how solids and liquids exert pressure horizontally?

Solids do not tend to deform and therefore do not exert horizontal pressure, whereas liquids, due to their ability to flow and deform, do exert pressure horizontally.

How can the experiment with the water bottle be used to explain real-world applications like dam construction?

The experiment with the water bottle demonstrates how pressure increases with depth in liquids, which is a principle used in dam construction to ensure that the structure can withstand the increased pressure at its base.