What Is Pressure?
Pressure is how hard something pushes on a surface. It tells us how much force is spread over a certain area. For example, air pushes on your skin all the time. That push is air pressure.
In science, pressure is a basic idea in physics and chemistry. It is used to study air, water, gases, weather, engines, tires and many other things in daily life.
Definition
Pressure is the force that acts on each unit of area.
In math form:
P = F / A
Where:
- P is pressure
- F is force
- A is area
This means, if the same force is spread over a smaller area, the pressure is higher. If the area is bigger, the pressure is lower.
The official SI unit for pressure is the pascal, written as Pa. One pascal is one newton of force on one square meter of area.
History / Origin
People have used the idea of pressure for a long time, even before they had a name for it. Ancient builders and sailors knew that water and air could push and crush objects.
In the 1600s, scientists started to study air and vacuum. Evangelista Torricelli showed that air has weight and creates pressure. Blaise Pascal studied how pressure changes with height and in liquids. The unit pascal was later named after him to honor his work.
Over time, scientists created tools like barometers and manometers to measure pressure more exactly. Different fields, such as engineering, weather science and medicine, added their own common pressure units and measuring methods.
Symbol & Abbreviation
Pressure itself is usually shown with the letter P in formulas.
Common units and their symbols for pressure include:
- Pascal, symbol Pa, the main SI unit
- Kilopascal, symbol kPa, 1 kPa is 1 000 Pa
- Megapascal, symbol MPa, 1 MPa is 1 000 000 Pa
- Bar, symbol bar
- Millibar, symbol mbar or mb
- Standard atmosphere, symbol atm
- Millimeters of mercury, symbol mmHg
- Torr, symbol Torr
- Pounds per square inch, symbol psi
Current Use Around the World
Today, the pascal is the main scientific unit for pressure all around the world. Most scientific papers, physics books and lab reports use pascals, kilopascals or megapascals.
Still, other units are often used in daily life:
- Weather reports often use hectopascals, hPa, or millibars. These two are equal in value.
- Tire pressure is often given in psi in the United States, and in bar or kPa in many other countries.
- Blood pressure is usually written in mmHg, millimeters of mercury.
- Divers and underwater workers often use bar and kPa.
- Vacuum systems and some lab devices may use Torr or mmHg.
Engineering, building design and industry usually try to follow the SI system, so they prefer pascal based units such as kPa and MPa.
Example Conversions
Here are some useful pressure conversions, rounded for easier use:
- 1 atm is about 101 325 Pa
- 1 atm is about 101.3 kPa
- 1 atm is about 1.013 bar
- 1 atm is about 760 mmHg
- 1 atm is about 14.7 psi
Other helpful examples:
- 1 bar is 100 000 Pa
- 1 kPa is 1 000 Pa
- 100 kPa is about 0.987 atm
- 1 psi is about 6 895 Pa
Typical real world pressures:
- Air pressure at sea level is about 101.3 kPa, 1 atm
- Car tire pressure is often around 200 to 250 kPa, about 30 to 36 psi
- Normal human blood pressure is about 120 over 80 mmHg
Related Units
These are the main units that measure pressure:
- Pascal, Pa the standard SI unit, used in science and engineering
- Kilopascal, kPa used in weather reports, engineering and vehicles
- Megapascal, MPa used for very high pressures, for example in materials testing
- Bar close to normal air pressure, often used in diving and industry
- Millibar, mbar used in meteorology, same size as hectopascal
- Atmosphere, atm based on average air pressure at sea level
- Millimeter of mercury, mmHg used for blood pressure and some lab work
- Torr almost the same as mmHg, used in vacuum science
- Pounds per square inch, psi common in the United States for tires and tools
All these units measure the same idea, pressure, they only use different size steps and names.
FAQs
What is a simple way to understand pressure?
Pressure tells you how strongly something pushes on a surface. If you stand on snow in normal shoes you sink, but with skis you spread your weight over a larger area, so the pressure is lower and you do not sink so much.
What is the formula for pressure?
The formula is P = F / A. Pressure equals force divided by area. Use newtons for force, square meters for area and you get pascals for pressure.
What is the SI unit of pressure?
The SI unit of pressure is the pascal, symbol Pa. One pascal is one newton of force on one square meter of area.
What is the difference between pressure and force?
Force is the total push or pull. Pressure is that force spread over some area. The same force can give high or low pressure depending on how small or large the area is.
What is atmospheric pressure?
Atmospheric pressure is the pressure of the air around Earth. At sea level it is about 101.3 kPa, 1 atm. It becomes lower when you go higher up a mountain or in an airplane.
Why are there so many units for pressure?
Different jobs and fields grew up with their own tools and habits. Medicine used mercury columns, so they still use mmHg. Weather studies used barometers, so they used millibars. Modern science uses pascals, but the older units stay in many places because people are used to them.
How is pressure measured?
Pressure is measured with devices called pressure gauges, barometers or manometers. Some use liquids like mercury or water. Others use springs or electronic sensors to show the pressure.
Is vacuum zero pressure?
A perfect vacuum would have zero pressure, no particles at all. In real life, we almost never reach perfect vacuum. We usually talk about low pressure compared to normal air pressure instead.
