##### Teaching Phase: How will the teacher present the concept or skill to students?

Students will follow the lesson instructions for activities that allow students to infer the effects of increasing net force or object mass (see Force, Mass, and Motion attachment).

During the first discussion, the teacher should ensure that students understand the definition of force and have recognized that the force they exerted on the marble caused it to move, so the forceÂ transferredÂ energy into the marble (in the form of kinetic energy).

During the second discussion, the teacher should ensure that students understand that magnetic force and gravitational force can act without contact and that friction is a force that acts to slow moving objects because it is in the opposite direction of the motion of an object. Students should understand Newton's First Law. They should realize that a net force is required to start motion in a stationary object or to change the speed or direction of a moving object.

During the third discussion, the teacher should ensure that students understand that speedÂ or direction will continue to change as long as a net force is applied to an object. Students should understand that when motion is observed over time intervals of the same size equal distances traveled indicates constant speed and different distances traveled indicates changes in speed. Increasing distances traveledÂ indicate positive acceleration and increasing speed. DecreasingÂ distances traveled indicate negative acceleration and decreasing speed. Students should realize that as long asÂ a net force is present, acceleration occurs.

After the first activity in Part 2, the teacher will introduce the video (attached) andÂ explain that air jet thrust is a push force that is produced by touch or contact between air pressure and an object such as a leaf blower or an aircraft propeller. Allow the students to watch the video and answer the questions. This would be a good place to discuss Newtonâ€™s third law of motion, showing that the blower pushing backward on the air and the air pushing forward on the blower/skateboard are a force pair.

During the fourth discussion, the teacher should ensure that students realize that both time and distance intervals can be measured using scientific instruments, including slow motion video. Students should comprehend that the relationship between time and distance can be show using a graph of measurements and that evidence of acceleration as a result of the application of a net force can be seen on the graph as changes in the distances traveled between observations of position when observations are made at equally spaced time intervals. Students should know that Newton's Second Law predicts that acceleration increases as net force increases, but decreases as the mass of the object increases. Students should be able to use the number line graphs to see that increasing the net force increases the distance traveled during each time interval. They should be able to see that increasing the mass of the object decreases the distance traveled during each time interval. Students should understand that thrust from an air jet is an example of aÂ contact force produced by air pressure.