Fast Facts
Baseballs travel farther in moist air than in dry air. For any given volume of air, moist air has exactly the same number of molecules as dry air at the same temperature and pressure.
Dry air is composed mostly of relatively heavy oxygen (O2) and nitrogen (N2) molecules. However, in moist air, some molecules are the lighter weight water molecules (H2O), rather than heavier O2 or N2 molecules.
Therefore, air is less dense when moist, and this results in less resistance to the ball's motion through air. So, for two baseballs hit with equal force, the one hit in the moist air would travel farther than the one hit in dry air.
Fast Facts
Baseballs travel farther in moist air than in dry air. For any given volume of air, moist air has exactly the same number of molecules as dry air at the same temperature and pressure.
Dry air is composed mostly of relatively heavy oxygen (O2) and nitrogen (N2) molecules. However, in moist air, some molecules are the lighter weight water molecules (H2O), rather than heavier O2 or N2 molecules.
Therefore, air is less dense when moist, and this results in less resistance to the ball's motion through air. So, for two baseballs hit with equal force, the one hit in the moist air would travel farther than the one hit in dry air.
Overview
To show that air has weight, the air is removed from one of two balanced balloons, throwing the balance off.
| TOTAL TIME | 10 minutes. |
|---|---|
| SUPPLIES | Yard/meter stick; two large balloons; string; transparent adhesive or masking tape |
| PRINTED/AV MATERIAL | None |
| TEACHER PREPARATION | You can have someone hold the string (attached to a year/meter stick) or you may want to have a piece of string hanging from the ceiling before class. |
| SAFETY FOCUS | Severe thunderstorm safety |
Procedure
- Inflate two balloons so they are the same size.
- Tape one balloon to each end of the yard/meter stick.
- Tie a string to the center of the stick and adjust it so the stick balances when held by the string. Tape the string in place to prevent it from slipping.
- Ask the students, "If one end were heavier, would the heavier end move up or down?"
- Carefully deflate the other balloon. Try poking the balloon with a pin in its neck to prevent the balloon from tearing apart as it pops.
- Let both balloons hang freely on the yard/meter stick. Ask the students to explain what happens to the balance.
Discussion
Air is all around us. This air is composed of atoms and molecules. Despite their small size, the quantity of atoms and molecules exert a weight on us known as pressure. Since our bodies are adapted to live in this environment, we do not notice the pressure.
Since the inflated balloon now weighs more than the deflated one (due to the air inside of the balloon), it will sink due to the imbalance. Now, imagine the weight of air if that balloon were the height of the atmosphere.
That is actually what is occurring at this moment in your classroom. When we measure air pressure with a barometer, we are measuring the weight of the column of air directly over us.
Building a Weather-Ready Nation
The weight of air molecules also affects the weather. One measure of the severity of a thunderstorm is the wind speed. The National Weather Service defines a severe thunderstorm as one containing wind speeds of 58 mph (50 kt / 93 km/h) or greater and/or hail size of 1" (2.5 cm) or greater.
At those wind speeds, the weight of the air molecules creates the force that knocks down phone and power lines, trees, vehicles, and people. When the National Weather Service issues a Severe Thunderstorm Warning, it means a thunderstorm with those hazardous conditions is occurring or about to occur near you.
Discuss severe thunderstorm safety with your family. Know where your safe rooms are. Know what to do in case all family members are not together. Preparing for a disaster ahead of time helps reduce fear and lets everyone know how to respond during a severe thunderstorm.
Take an American Red Cross first aid and CPR course to learn how to treat burns and administer CPR. You need to know how to respond in an emergency because severe weather can strike almost anywhere in the country.
Fast Facts
Baseballs travel farther in moist air than in dry air. For any given volume of air, moist air has exactly the same number of molecules as dry air at the same temperature and pressure.
Dry air is composed mostly of relatively heavy oxygen (O2) and nitrogen (N2) molecules. However, in moist air, some molecules are the lighter weight water molecules (H2O), rather than heavier O2 or N2 molecules.
Therefore, air is less dense when moist, and this results in less resistance to the ball's motion through air. So, for two baseballs hit with equal force, the one hit in the moist air would travel farther than the one hit in dry air.