Students learn how force is needed to overcome inertia in order to stop or start objects in motion, how friction and gravity affect how objects move, and how forces work in pairs. Students learn that gravity is a force that makes every object attract every other object. The attraction increases as the mass of an object increases, and decreases as distance between the objects increases. Students learn that friction between surfaces or as air resistance slows the motion of objects and can be controlled. By the end of eighth grade, students will develop an understanding of motion and forces.
Students observe the motion of a pendulum.
They explore ways of changing the pendulum's motion and observe the relationship between the motion of the pendulum and the force it exerts on dominoes. Students measure the amount of force needed to move different objects by measuring the length to which a rubber band stretches before the force applied to the rubber band causes each object to move. Students will infer that more force is required to move objects with greater mass or to move objects across rough surfaces. Students study the effects of friction by measuring the height to which a board must be raised to allow an object to slide along its surface. Students build a rocket that is propelled by a balloon.