MYP Physics Topic Pressure Revision Notes

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MYP Physics Topic Pressure Revision Notes | RevisionDojo

Why Does The Same Force Sometimes Cause Very Different Effects?

Definition

Pressure

Pressure is force exerted per unit area on a surface.

Pressure describes how concentrated a force is when it acts on a surface.
The effect of a force depends not only on how large the force is, but also on the size of the area over which it is applied.
A force acting on a small area produces a larger effect than the same force acting on a larger area.
Pressure helps explain everyday experiences such as cutting, piercing, and sinking.

Example

Walking barefoot on sand feels easier than walking on sharp shingle.
Your weight (force) is similar in both situations, but the contact area is much smaller on the sharp stones, so the pressure on your skin is larger.

Calculating Pressure

In the simplest situations, pressure is calculated using

$$P=\frac{F}{A}$$

where $P$ is pressure, $F$ is the force acting perpendicular (normal) to the surface, and $A$ is the contact area.

Relationship Between Pressure, Force, and Area

Pressure increases when a force is applied over a smaller contact area.
Pressure decreases when the same force is spread over a larger contact area.
Both force and area must be considered together to understand pressure.

Note

Changing the contact area changes the pressure even if the force remains constant.

Units And Conversions Matter

The SI unit of pressure is the pascal (Pa): $$1\ \mathrm{Pa}=1\ \mathrm{N\ m^{-2}}$$
In everyday contexts, you often see:
1. kPa: $1\ \mathrm{kPa}=10^3\ \mathrm{Pa}$
2. MPa: $1\ \mathrm{MPa}=10^6\ \mathrm{Pa}$
3. hPa (hectopascal): $1\ \mathrm{hPa}=100\ \mathrm{Pa}$ (common in weather maps)
4. bar: $1\ \mathrm{bar}=10^5\ \mathrm{Pa}$ (so $1\ \mathrm{mbar}=1\ \mathrm{hPa}$)

Common Mistake

Forgetting to convert areas into $\mathrm{m^2}$ because area depends on length squared, converting cm to m changes the numerical value a lot.

A Small Area Creates A Huge Pressure

When a force is concentrated onto a tiny area, the pressure can become enormous.
This is why sharp tools work as they create high pressure at the cutting edge.

Exam technique

Whenever you see pressure questions, write the units beside each value before substituting.
If your final unit is not $\mathrm{Pa}$ (or an equivalent like $\mathrm{N\ m^{-2}}$), you have probably used the wrong area unit.

What Is Atmospheric Pressure?

Definition

Atmospheric pressure

Atmospheric pressure is the pressure exerted by the weight of the air above a surface.

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MYP Physics Pressure Notes

Why Does The Same Force Sometimes Cause Very Different Effects?

Calculating Pressure

Relationship Between Pressure, Force, and Area

Units And Conversions Matter

A Small Area Creates A Huge Pressure

What Is Atmospheric Pressure?

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Why Does The Same Force Sometimes Cause Very Different Effects?

Calculating Pressure

Relationship Between Pressure, Force, and Area

Units And Conversions Matter

A Small Area Creates A Huge Pressure

What Is Atmospheric Pressure?

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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Forces and energy8 subtopics

Heat, light and sound6 subtopics

Electromagnetism9 subtopics

Waves5 subtopics

Astrophysics3 subtopics

Atomic physics2 subtopics

MYP Physics Pressure Notes

Forces and energy8 subtopics

Heat, light and sound6 subtopics

Electromagnetism9 subtopics

Waves5 subtopics

Astrophysics3 subtopics

Atomic physics2 subtopics

Why Does The Same Force Sometimes Cause Very Different Effects?

Calculating Pressure

Relationship Between Pressure, Force, and Area

Units And Conversions Matter

A Small Area Creates A Huge Pressure

What Is Atmospheric Pressure?

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Why Does The Same Force Sometimes Cause Very Different Effects?

Calculating Pressure

Relationship Between Pressure, Force, and Area

Units And Conversions Matter

A Small Area Creates A Huge Pressure

What Is Atmospheric Pressure?

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account