# atmospheric pressure

• Pictured: taken by astronauts aboard the International Space Station (ISS) of the Earth’s atmosphere as seen from orbit. The Earth’s curvature is visible along the horizon. Above the darkened surface of the Earth, a brilliant sequence of colors roughly denotes several layers of the atmosphere.

Atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth’s gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation).

Atmospheric pressure is the total weight of the air above unit area at the point where the pressure is measured. Air pressure varies with location and weather. The average atmospheric pressure at sea level is about 1 atmosphere (atm) which can be measured and reported as:

• 101.3 kPa (kilopascals)
• 14.7 psi (pounds per square inch)
• 760 torr
• 29.92 inches of mercury (symbol Hg).

The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space.

• An altitude of 120 km (75 mi) is where atmospheric effects become noticeable during atmospheric reentry of spacecraft.
• The Kármán line, at 100 km (62 mi), also is often regarded as the boundary between atmosphere and outer space.

What’s the problem?

How strong does a soda can need to be to resist being crushed by atmospheric pressure? Soda cans are made from a thin cylinder of aluminum. When the can is full, the soda is carbonated and produces air pressure. Normal atmospheric pressure is pressing against the outside of the can.

• Ask – What pressure difference does it take to crush a soda can?
• Imagine – What is a simple way to decrease the pressure on the inside of a soda can? What would happen if there is a big pressure difference?
• Design, Build – Boiling water in an enclosed space like a empty soda will trap most of the steam or eater vapor inside the can – some will escape out the opening but most will stay inside. Inverting the can into a beaker of water traps the steam inside. The cold water cools the steam with reduces the pressure inside the can. The can is “crushed” by the atmospheric pressure that is now greater than the pressure in the can.
• Improve – Reducing the amount of aluminum in each soda can reduces the cost of manufacturing and shipping.

Engineering ideas

• atmosphere (atm), kPa (kilopascals), psi (pounds per square inch), torr, inches of mercury (symbol Hg), space, atmosphere

Do It
Challenges for you to work on…