Pressure

Pressure is a measure of the amount of force placed on an area. The only thing is that the force does not have a direction. The amount of force can be calculated, but not the direction as the force is in all directions.

There are many ways of speaking about pressure, such as Pascals, newtons per square meter, or pounds per square inch and others.

hot-air-balloon

If you blow up a balloon, the gas inside is putting pressure everywhere inside the balloon. If you measure the pressure, it will be the same no matter where on the surface you measure.

Air pressure is the weight of air molecules pressing down on Earth and is the greatest because the air molecules are the closest together at sea level. Air pressure lessens as you move away from sea level upwards to distances above ground and lessens more over mountains.

Scientists called meteorologists study air pressure and air movements over the land and oceans to forecast weather.

They use barometers to measure the air pressure at different places and different times of day. A barometer is a tube with mercury inside. The air pressure makes the mercury move up or down in the tube and the movements are recorded in inches or centimeters.

By measuring air pressure, meteorologists can make a good guess or prediction as to when the air pressure changes in a place. They can tell when rain or snow is expected or when winds could cause damage, such as tornadoes and hurricanes. They can also predict the speed of the winds and the direction.

tornado-bottle

Meteorologists can give warnings to people in the path of a storm and warn airline pilots to expect turbulent winds. They can warn ship captains of sea storms that are brewing in the path of their ships.

There is pressure under the sea. The weight of the water puts pressure on anything under it: the greater the depth, the greater the pressure. For every 10 meters under water, there is an additional 6.47 kg of pressure on every square inch of surface of an object.

Anyone exploring deep under the ocean must wear or be inside specially designed equipment and oxygen.

Here’s a scary thought: If you didn’t have special equipment when you went 2,000 meters under the ocean, there would be more than a ton of pressure being put on every square inch of your body. In other words, you would be squashed flat.

Here are two experiments you can try. Make sure an adult is supervising.

Pressure Experiment 1!

Fill a glass one third full of water. Put a piece of cardboard over the top and place your palm over the cardboard. Then tip the glass upside down!

Result: no water escapes because the water inside the cup is lighter than the air around the glass.

science-experiments-kids

Pressure Experiment 2!

Fill a 2-liter pop bottle half full of water. Put a long straw into the mouth of the bottle and make a seal of tape over the bottle top and sticking to the straw. Now blow into the straw to increase the air pressure inside the pop bottle.

Result: The air pressure inside the bottle will push the water out of the straw.

Questions:

  1. Name two ways of speaking about air pressure.
  2. Why is air pressure greatest at sea level?
  3. What do meteorologists do?
  4. Why is it important to know when a storm is heading your way?
  5. Why do you need special equipment to explore deep beneath the sea?

thunderstorm

Answers:

  1. Air pressure can be expressed in Pascals or pounds per square inch.
  2. Air pressure is greatest at sea level because the molecules of air are the closest together.
  3. Meteorologists can predict the weather.
  4. If you know a storm is in your path, you can change your position or find protection.
  5. Pressure is very high deep beneath the sea and you need protection and oxygen to travel there.

Physics