Air Pressure/Inertia - Air Mass Matter (Chelsey Traylor)

Author

Chelsey Traylor

Principle(s) Illustrated

1. Air has mass.

2. Gases have mass, occupy space, and exert pressure.

3. Inertia is the tendency of a body at rest to stay at rest until acted upon by an unbalanced force.

Standards

• 8.3.d. States of matter (solid, liquid, and gas) depend on molecular motion.

• 8.2.c. When the forces on an object are balanced, the motion of the object does not change.

• 8.3.e. In gases, the atoms and molecules are free to move independently, colliding frequently.

Questioning Script

Prior knowledge & experience:

All matter has both mass and volume. Gases are composed of molecules that are separated by an "empty" space. Inertia is the tendency of an object at rest to stay at rest.

Root question:

What happens to a stick placed under newspaper that is struck at different pressures? Students will predict what happens when a stick is placed 10 cm over the edge of a table and is struck quickly by the hand. Then, this is repeated except the stick is placed under some newspaper. The students will predict what happens. Then, the teacher uses different pressures to touch or strike the stick so students can observe differences in touch pressure.

Target response:

The stick will break in half when struck quickly underneath several sheets of newspaper. The stick is pushing up on the weight of the column of air . Inertia causes the paper to remain at rest and rapidly moving end of the stick keeps moving. When the stick is pushed at a slow pace, the air that seeps under the newspaper can counterbalance the air pressure on top of the paper and the stick can easily lift up the paper.

Air pressure = force/area = weight of the column of air/surface area

Common Misconceptions:

Air does not have a mass. Gases are not anything.

Photographs and Movies

References

Reference 1: Brain Powered Science - NSTA

Reference 2: UBC Physics