4.3b Pressure as Force per unit Area | AS Pressure | Cambridge A Level Physics

Summary

This video explains key concepts of pressure and density, using a boba drink as an analogy. It begins with an introduction to density and its relation to mixtures, before diving into pressure, which is defined as force per unit area. The video uses real-life examples, such as high heels and narrow shoes, to illustrate how pressure varies with area. The discussion also covers hydrostatic pressure, demonstrating its relationship with height and fluid density. Viewers are encouraged to think about how these concepts apply in real-world scenarios, with a promise to further explore hydrostatic pressure in the next video.

Takeaways

• 😀 Density is important for understanding mixtures of liquids, such as in boba drinks, which consist of different layers of liquids and suspended solids.
• 😀 Pressure is defined as force per unit area, and it is influenced by the size of the area on which the force is applied.
• 😀 Small areas lead to higher pressure, which is why high heels, with their narrow heels, can cause discomfort by concentrating pressure on a small area of your feet.
• 😀 To reduce pressure on your feet, it’s better to wear shoes with a wider base, as they distribute the force more evenly.
• 😀 The relationship between pressure and area is inversely proportional: as the area decreases, pressure increases.
• 😀 Heavier individuals exert more force, which leads to higher pressure, as pressure is directly related to force.
• 😀 The formula for pressure is given by Pressure = Force / Area, and it is measured in Pascals (Pa) or Newton per meter squared.
• 😀 Pressure is a scalar quantity, meaning it does not have a direction, unlike force which is directional.
• 😀 When dealing with inclined planes, the force acting on an object is not fully perpendicular to the surface. To calculate pressure, we need to resolve the force into its perpendicular component.
• 😀 In fluid mechanics, hydrostatic pressure increases with depth. This is demonstrated in the water cylinder experiment, where water from the lowest hole shoots the furthest due to greater pressure at greater depths.

Q & A

What is the relationship between pressure and area?

Pressure has an inverse relationship with area. If the area is small, the pressure is large, and if the area is large, the pressure is small.

How does wearing narrow shoes affect pressure on your feet?

Narrow shoes exert a larger pressure on your feet because the area in contact with the floor is small, which increases the pressure, potentially causing discomfort.

Why do people prefer shoes with a wider base?

People prefer shoes with a wider base because it reduces pressure on the feet, offering more stability and comfort by distributing the force over a larger area.

What unit is used to measure pressure?

Pressure is measured in Pascals (Pa), which is equivalent to Newtons per square meter (N/m²).

What happens to the pressure if the force applied increases?

As the force applied increases, the pressure also increases, as pressure is directly proportional to the force.

How does the orientation of a surface affect the pressure exerted on it?

The pressure exerted depends on the component of the force that acts perpendicular to the surface. For inclined planes, you need to resolve the force into components to find the pressure that is perpendicular to the surface.

What does the term 'perpendicular force' mean in the context of pressure?

A perpendicular force refers to the force component that is directed at a 90-degree angle to the surface. Only this component of the force contributes to pressure exerted on the surface.

What happens to the pressure in a fluid as the height of the fluid increases?

As the height of the fluid increases, the pressure at the bottom of the fluid also increases. This is because pressure in a fluid is related to the height and density of the fluid.

How is hydrostatic pressure related to the height of the fluid?

Hydrostatic pressure increases with height because the deeper you go into a fluid, the more weight of the fluid is exerting force on the area below.

What did the experiment with the water cylinder demonstrate?

The experiment showed that the water at the lowest part of the cylinder shoots the furthest, indicating that the pressure is greater at the bottom due to the height of the water above it.