This lesson introduces students of any age to introductory physics.  This fun activity leads into a customizable lesson that can be tailored to most elementary grades.

Lesson Title

Forces and Interactions


Kindergarten and/or 3rd Grade Science (physics)

Materials needed

  • hairdryer
  • lightweight ball such as a ping pong ball


  • Students will observe the concept of force and its interaction with Earth’s gravity.
  • Students will observe the interaction between higher air pressure and the pull of gravity.
  • Students will develop an understanding of Newton’s law of action and reaction: 3rd law: for every action there must be an equal and opposite reaction.


Kindergarten: Forces and Interactions, Pushes and Pulls

K-PS2-1:       Plan and conduct an investigation to compare the effects of different strengths or different directions of pushes and pulls on the motion of an object.

K-PS2-2:       Analyze data to determine if a design solution works as intended to change the speed or direction of an object with a push or a pull.

Grade 3: Forces and Interactions

3-PS2-1:       Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object.

Anticipatory set

  • Kindergarten: use a diagramming exercise to focus students’ attention on the class objectives.
  • Third grade: use brainstorming techniques and a Writing to Learn (WTL) exercises to focus students’ attention on the class objectives.


Discuss the concepts of gravity, force, air pressure, action and reaction.

Pose questions to engage students. Have students brainstorm and either write down (grade 3) or discuss (kindergarten) theories that may answer the questions.  Pose more complicated questions to grade 3 students.  Questions may include: How does gravity keep us on the ground? What happens if we don’t have gravity?  How does the concept of force relate to gravity?  How do things float?  Can we make something float despite gravity, and if so, how?

  • Grade 3: Conduct the demonstration and ask questions to further understanding: what do you think will happen to the ball when we put it in the air stream? What will happen if we try to pull the ball out of the air stream?  Why do you think the ball can float?  Is the force of gravity still in effect?  What is the “action” and what is the “reaction”?
  • Kindergarten: Conduct the demonstration and have the students draw what they see. As you discuss action and reaction, have the students diagram using arrows and other symbols to display what they believe is happening, i.e. gravity versus air pressure.


  • Angle the blow dryer in an upright position and turn the speed on to its highest level.
  • Carefully position the ping pong ball in the air stream, then let go.
  • Move the blow dryer slowly and carefully to demonstrate how the ball will move in sequence with the blow dryer. (Further thinking #1)
  • Have a student slowly and carefully attempt to move the ball out of the air stream. (Further thinking #2)
  • Attempt to tilt the air stream to one side and see if the ball stays suspended. (Further thinking #3)
  • Have a student attempt to add another ball to the air flow. (Further thinking #4)


As the experiment is conducted, have students hypothesize outcomes for each “Further thinking” application. Use the hook, “What would happen if…?”

  • Explain: the airflow from the blow dryer pushes the ping pong ball upwards until its upward force equals the force of gravity pushing down on it. When it reaches this point, it gently bounces around, floating when the upward and downward forces are equal.
  • Explain: the reason the ping pong ball stays nicely inside the column of air produced by the blow dryer without shifting sideways is due to air pressure. The fast moving air from the hair dryer creates a column of lower air pressure.  The surrounding higher air pressure forces the ping pong ball to stay inside this column, making it easy to move the blow dryer around without losing control of the ball.
  • Compare: What else works similarly to this concept? The outward-flowing air exerts an inward force on the ball, just like the downward flow of air beneath a helicopter exerts an upward force on the blades of the helicopter.
  • What does it mean when the wavy lines on the paper are higher or lower? How could you use that to measure an earthquake?  Example: height of the largest waves indicates the size of an earthquake.
  • How can scientists use seismographs all over the world to pinpoint the location of an earthquake? Think about ripples in a pond or GPS systems.  Example: length of the earthquake record and the arrival times of each wave, the distance of the focus from the recording point can be determined.
  • What parts of the activity emulate how a true earthquake occurs? What are some of the problems an earthquake causes?  Examples: destruction of buildings, larger earthquakes causing small changes to Earth’s orbit, etc.

What to do next time

  • Have the students consider ways to improve the activity, or present new ways to test action and reaction.