The first law describes inertia: unless acted upon by an outside force, an object in motion remains in motion and an object at rest remains at rest. The second law deals with velocity and the external forces necessary to change an object's velocity. The third law posits that every action, or release of force, has an equal and opposite reaction.
Create a small seesaw by centering a board on a raised support with one end elevated. How long will the board remain in that position? Place a small weight on the raised end of board. What happens to the board? The weight acts as an outside force on the stationary board, putting it into motion. What was the action? The reaction?
Point out that both, the added weight and the presence of the table beneath the board, contribute to the changes. Place a slightly heavier weight on the other end and discuss the results. What happened to the lighter weight? Add another small weight to the lighter end. Is the total weight of that end greater or lesser than the other end? Which force acts more strongly on the board's position? Does the number of weights matter more than the total of the weights? Does the position of the weight relative to the end of the board make a difference?
Suspend a board horizontally between two supports. Place a weight at one end of the board. Inertia causes the weight to remain in place. Gently remove the support at the opposite end of the board and rest the board on the table at an angle. Is the pull of gravity sufficient to put the weight into motion over the forces of inertia and friction? Increase the angle of the board by lifting the upper end even higher, which increases the force of gravity. Does the change in angle change the movement of the weight?
Place the upper end of the board back on the support. Place two objects of differing weight but same shape at the top of the board. The velocity will depend on the angle of the board, but the heavier weight receives more influence from gravity, the force acting on the mass of the weights. Which one moves faster? Now use two objects of the same weight but one flat and one round. Does the difference in shape change how the weights reacts to the incline? Friction's influence on objects depends in part on the shape and texture of the object.
Line up a number of articles of differing mass. Mark another line 6 feet away. Have students push each object in turn across the opposite line to see how different objects require different amount of force to overcome inertia. Does it take more force to make something move quickly than to move it slowly?
Blow up a balloon. Tie it off and place it on a flat surface at a marked point. Blow a puff of air against the balloon. Measure how far it moves. Replace the balloon on the mark and tap it with one finger, slap it with a flat hand, punch it. How does the differing amount of force change how fast or how far the balloon travels? According to Newton, the amount of applied force and size of the mass work together to determine acceleration.
Blow up a balloon and release it into the air. How does the escaping air make the balloon behave? The action of air escaping from the balloon forces the reaction of the balloon flying around the room. How does this principle apply to space travel?