Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Pressure

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Pressure

Have you ever wondered why the sharp edge of a knife can cut through a fruit seamlessly whereas if you used the blunt edge it would require a lot more effort? This phenomenon can be explained by understanding the concept of pressure. In this case, information about the magnitude of the force that is exerted by the knife is not enough to know whether or not cutting fruit is easy or not. We need another measure that quantifies how much force is exerted over a particular area. At the end of this article, you will have learned what pressure is, learned how to use the pressure equation, and worked on a few examples to understand the importance of pressure in our daily lives.

Pressure definition

Before we introduce the formula for pressure and look at some worked examples, let us first define what we mean by pressure in physics.

Pressure is defined as the force exerted per unit area of a surface.

The amount of force exerted by a knife is not enough information to know whether or not we will be able to cut into a fruit. Pressure takes into account how concentrated the force is over a particular area.

Pressure formula

So how do we calculate the concentration of force in a given area? Simple, we know that pressure is nothing but the force acting per unit area which in mathematical terms give

or in words

Pressure is expressed in Pascals (),is the force in, and the area is measured in units of.

Pressure The image shows the concentration of forces with respect to area StudySmarter
These knives have different contact areas with the surface, the sharper knife exerts more pressure for a given amount of force because the force is acting over a smaller surface area, StudySmarter Originals

A pressure ofcan be defined as a force ofacting on an area of(unit area). The above formula is only valid when the force acts at right angles to the surface. As you can see from the equation. Pressure is directly proportional to the force applied and inversely proportional to the area on which it acts. This means that to increase the pressure we can either

  • Increase the force keeping the area constant or

  • Decrease the area keeping the force at a constant.

Pressure Diagram comparing a hammer hitting on a basketball and a nail StudySmarterAs the area of contact decreases, the pressure increases provided the force remains the same, this allows the nail to be driven into the wall, StudySmarter Originals

Units of pressure

The SI unit of pressure is1 Pascal =. For large quantities of pressure, we can use and. You may also see other units of pressure such as torr,

The atmospheric pressure is a commonly used unit (). The pressure exerted by the Earth's atmosphere on the surface of the earth is what is known as atmospheric pressure. The atmospheric pressure in pascals is equal to. It is also sometimes referred to as standard atmospheric pressure.

Types of pressure

Pressure can be exerted by solids, liquids, and gases. Solids exert pressure through their point of contact. Liquids and gases exert pressure on a solid due to the collision of their particles with the solid.

  • A nail being hammered into a wall is an example of pressure acting from one solid onto another solid.
  • We are constantly facing the force of the atmosphere on our bodies. which is nothing more than the pressure exerted by the gases in the atmosphere.

The pressure exerted by liquids

The pressure exerted by liquids is mainly due to the weight of the liquid. Imagine taking a dive at your local swimming pool. Let's say you dive into the deep end. Now due to the effects of gravity, all of the weight of the water above you will act to press the water molecules down onto your body and any other object submerged in the water. This pressing is what we mean by the pressure exerted due to a liquid. The number of water molecules that are present above you will increase as you keep going deeper. This is why the pressure exerted by liquids increases with increasing depth and it's why the pressure you feel increases as you dive deeper into a body of water. Another factor that comes into play is the density of the liquid. Since density measures the mass per unit volume of a liquid. Liquids with higher density will exert a larger pressure at the same depths due to their larger weights.

Pressure A diagram showing pressure in liquids StudySmarterThe pressure exerted at a particular depth on a base Area A can be calculated by considering the weight of the column of liquid directly above A, StudySmarter Originals.

Lets now consider how to calculate the pressure exerted by a liquid at a particular depth. We consider a rectangular column of water with a base areaand height.

We already know that the formula for pressure is:

The weight of the liquid situated directly above the base area of considerationis given by the following equation:

Or in words

The next step in our calculation was considered to consider the density of the liquid in order to calculate the mass of the column of water:

,

or in words,

.

Rearranging for mass we get:

.

The volume of a cuboid can be written as the product of its base areaand its height:

,

or in words,

.

We Substitute the formula for weight in terms of mass before substituting the formula for mass in terms of density and volume. Finally, we substitute the formula for volume in terms of base area and height into the equation for pressure:

After further rearrangement, we arrive at the formula for the pressure exerted by a column of liquid pressure in terms of the density of the liquid, the height of the column of liquid, and the base area of the column of liquid:

Where pressure is measured in Pascals (), the depth or height of columnin meters () and densityinand gravitational field strength,in.

Next, let us look at a few examples where we use these formulas to calculate the pressure.

Atmospheric pressure

Atmospheric pressure is due to the air molecules in the atmosphere colliding with the earth or any other object contained within. The atmospheric pressure reduces as the altitude increases because the density of the air decreases at higher altitudes. At higher altitudes, there is less air, therefore the weight of the air pressing down on an object is reduced. This is the reason why some people experience ear pain during air travel that occurs due to quick changes in air pressure. The atmospheric pressure can be calculated using the same formula as the pressure due to liquids.

Pressure A cube diagram indicating the atmospheric pressure StudySmarterAtmospheric pressure is due to the weight of the air molecules directly above the surface of the Earth, StudySmarter originals

Examples of pressure

A fluid has a weight ofwhich is exerted over a surface area of. Calculate the pressure acting on the surface.

Calculate the pressure exerted on the ground by a person weighingwearing

  • A flat shoe with a contact area of
  • A heeled shoe with a total contact area of

What can you infer from the results?

Pressure A diagram that has a man shoe and heels side to side StudySmarterHeels vs Flat shoes, Nidhish Gokuldas StudySmarter Originals

Unit conversion

Pressure on the ground due to flat shoes

Pressure on the ground due to heels

The pressure exerted by the heels is almost 5 times that of the flat sole shoes. This is the reason why heeled shoes are uncomfortable to wear over long periods as they exert a large amount of pressure on the ground and equally on the persons who's wearing the shoe's feet.

Calculate the pressure in the water well at a depth of. Take the density of water to be

Step 1: List the given quantities

Step 2: Calculate the pressure using the appropriate equation

Calculate the density of air at an altitude ofwhere the pressure of the surrounding atmosphere is

Step 1: List the given quantities

Step 2: Calculate the pressure using the appropriate equation

Pressure - Key takeaways

  • Pressure is defined as the force exerted per unit area of a surface.
  • Pressure can be calculated by dividing the force by the area across which it is acting:

    or in words, .

  • The pressure exerted by a liquid is given by .

  • The pressure exerted by a liquid increases as the depth increases.

  • Atmospheric pressure is due to the weight of the air molecules on top of the earth.

  • Atmospheric pressure reduces as the altitude increases.

Frequently Asked Questions about Pressure

Pressure is defined as the force per unit area.

The formula for pressure is P=F/A

The formula for pressure is P=F/A

A knife cutting a slab of butter, A nail being hammered into a wall are examples of pressure

The types of pressure are 

  • Absolute pressure.
  • Gauge pressure.
  • Differential pressure.
  • Sealed pressure or vacuum pressure.

Final Pressure Quiz

Question

The formula for pressure is ...

Show answer

Answer


Show question

Question

The unit for pressure ...

Show answer

Answer

Pascal

Show question

Question

What happens to pressure when the area increases?

Show answer

Answer

It decreases

Show question

Question

What happens to pressure when force increases?

Show answer

Answer

It increases

Show question

Question

The atmospheric pressure increases as altitude increases.

Show answer

Answer

False

Show question

Question

The pressure in liquids decreases as the depth increases.

Show answer

Answer

False

Show question

Question

The weight of a  industrial machine is spread over . What is the pressure it exerts?


Show answer

Answer


Show question

Question

What are the correct units of pressure?


Show answer

Answer

All the option

Show question

Question

Which situation exerts the highest pressure?

Show answer

Answer

Nails hammered on a wall

Show question

Question

 is equal to ...

Show answer

Answer


Show question

Question

What is an example of pressure?

Show answer

Answer

Examples of pressure are

  • A nail being hammered into a wall
  • Knife cutting a fruit
  • Atmospheric pressure

Show question

Question

Calculate the pressure in the water well at a depth of . Take the density of water as


Show answer

Answer


Show question

Question

A fluid exerts a force of  over an area of . Calculate the pressure on the surface.


Show answer

Answer


Show question

Question

Calculate the density of air at an altitude of  where the atmospheric pressure is 

Show answer

Answer


Show question

Question

The pressure exerted by an object on the ground will be the same on the earth and the moon.

Show answer

Answer

False

Show question

60%

of the users don't pass the Pressure quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Just Signed up?

Yes
No, I'll do it now

Sign up to highlight and take notes. It’s 100% free.