Force and Motion Cover Photo
  • What’s in This Unit?

    Scientists send research instruments into space to collect data on astrophysical objects such as stars, planets, moons, and asteroids. These missions are incredibly expensive and require precise and meticulous planning to avoid failure. The teams of scientists and engineers who work together to design and build the spacecraft usually plan successful missions, but occasionally, costly mishaps occur. When these happen, scientists carefully investigate what went wrong, wanting to avoid future mistakes. In this unit, students engage in authentic work as they take on the role of student physicists working for the fictional Universal Space Agency (USA). They are called upon to assist in the investigation of one recent mishap. Students apply their developing knowledge of force and motion to explain why a space pod failed to dock at the space station as planned. This mystery serves as the anchor phenomenon for the unit. As they investigate, students will learn about the relationship between force, change in velocity, mass, and the equal and opposite forces exerted during collisions. This complex physics reasoning will be reinforced by the Force and Motion Simulation, a digital environment in which students can manipulate the mass of objects, their initial velocities, and the forces exerted on them as they observe the resulting change in motion. Students can also use this digital tool to simulate collisions and see how different objects are affected during these events. With this digital tool, students gather data about how forces affect the motion of objects, which they use as evidence to explain what happened to the pod. By the end of the unit, students will understand how forces can affect the motion of objects.



    This unit provides students with an exciting context in which to consider forces, motion, and collisions: outer space. Students are naturally curious about space and the new frontier of innovation in space exploration. They are fascinated by the fictional problem of the docking mishap, and they are motivated to apply their understanding of the relationship between mass, force, and changes in velocity to this mystery. The setting of deep space allows us to create a scenario where students can think deeply about one-dimensional collisions without the complications of friction or strong gravitational attraction. Most middle school physics units use a series of narrowly defined contexts, such as hockey and billiards, for creating their examples. This unit provides one broad, central context for the content knowledge and puts meaningful application of Newton’s laws within the reach of middle school students’ understanding by inviting them to explain a mystery through engaging in the reasoning and practices of a real-world science role. Throughout the unit, examples of earthly forces, especially those cited in the articles, give students opportunities to apply their thinking to more familiar situations.



    The Force and Motion unit begins as students are introduced to the fictional problem. Scientists at the Universal Space Agency lost communication with an asteroid-sample-collecting pod, just as it was preparing to dock and deliver its samples to a space station. Students are challenged to figure out why the pod ended up moving in the opposite direction rather than docking. Explaining this unexpected result in the pod’s motion is broken down into smaller problems over the course of three chapters.

    In Chapter 1, students work to answer the question, What caused the pod to change direction? They begin by investigating the relationship between the force exerted on an object and the object’s change in velocity. Students apply forces to stationary and moving objects and observe the resulting changes in velocity, using both physical materials and the digital simulation. They conclude that forces exerted in different directions will cause different types of velocity changes and different strength forces will cause different amounts of velocity change. Students consider how the force exerted by the thrusters might have played a role in the pod's unexpected velocity change.

    In Chapter 2, students work to determine why this pod moved differently when its thrusters exerted the same strength force as thrusters on other pods. Students follow up by asking whether the pod's mass might be a consideration since the thrusters had a very different effect on this pod’s velocity. In the digital simulation and in hands-on tests using physical materials, students apply equal strength forces to objects of different mass and observe the resulting changes in velocity. Students also read an article about designing wheelchairs for different purposes in order to gather additional evidence about the relationship between mass, force, and changes in velocity. Students conclude that if the same strength force is exerted on objects of different mass, the force will cause the greatest velocity change in the object with the least mass. Students learn that this pod was more massive than pods on previous missions, which allows them to conclude that the same strength force exerted by the thrusters only slowed the pod, so it collided with the space station.

    In Chapter 3, students learn that not only is the pod moving, but the space station is also moving as a result of the collision. Students then gather evidence about the pod’s motion compared to the motion of the space station. Students read an article about collisions and directly observe collisions between objects of equal mass and objects of different mass in the digital simulation and in a hands-on test using physical materials. Students learn that every collision involves a pair of forces that are equal in strength, but opposite in direction. Students use concepts from all three chapters to develop an explanation for why the Universal Space Agency’s asteroid-collecting pod moved quickly away from the space station after the collision.

    In Chapter 4, students apply all they have learned about force, mass, and velocity to explain a new phenomenon. They are tasked to determine the difference between a collision scene in a film and a film student's attempt to recreate that scene. Students analyze evidence provided by the film student as they reason through the possibilities and try to pin down why her attempt to recreate the movie scene failed. In the Science Seminar, students cite their evidence and reasoning as they debate the differences between the test scene and the film.