Discuss force and air resistance. Elicit how air resistance depends on velocity and area. Elicit how air resistance is directly proportional to speed and frontal area. Define terminal speed and how acceleration becomes zero at terminal speed and the velocity becomes constant. introduce force interactions, action force and reaction force. Discuss friction as the force necessary for motion. Redefine force in terms of mass and acceleration. Note that acceleration is directly proportional to the force and inversely proportional to the mass. Demo action/reactions forces using a balloon.