Anchor Phenomena: For every force between colliding objects, there is an equal and opposite force, related to mass.
To engage students, they are introduced to Newton’s Third Law, that every action has a reaction, through a video of Gene Cernan’s spacewalk during the Gemini 9 mission. The system shown in the video is an astronaut and his space capsule. The students ask questions about why the spacewalk was so difficult and why he was repelled from the space capsule. They may ask questions about why that does not happen here on Earth, we are not repelled when we push on things, why not?
Students explore Newton’s Third Law through investigations of several systems. First, students explore by gathering information and diagramming the forces and motion in the following systems: walking, swimming, and a space shuttle launching. Students should use their diagrams to construct an explanation for the motion of the objects. Through class discussions, a definition of Newton’s Third Law begins to form. Students use evidence of what they have observed to state and write that each action in the above systems has an opposite reaction. Next, students gather information and make a force diagram two more systems, Newton’s cradle and balloon rockets, to explore that each reaction is equal to the initial action. Through class discussion, students should be able to fully explain what Newton’s Third Law is by this point. Students are shown a video of crash test dummies wearing seatbelts. The students use their constructed definition of Newton’s Third Law to explain why the seat belt and airbag are able to keep the crash test dummies in the car and safe.
The previous explorations should allow the students to see that every action does indeed have a reaction, but some of them will notice that every reaction may not create equal motion. For example, the spacewalk video in Episode 1, where Astronaut Cernan was repelled from the spacecraft when he pushed a button, but we are not repelled when we push buttons here on Earth. These observations lead to the next question: does the mass of an object actually change the reaction force? Students investigate how mass affects the reaction force by performing a few tasks while standing on the ground and then again while they are on wheels. Students explain why they move while on wheels, but not on the ground. Students learn that objects with different masses still follow Newton’s Third Law, but the motion/acceleration created by the reaction force is not equal if one object has far more mass than the other.
Students elaborate on their understanding of Newton’s Third Law by designing a solution and building something for this standard. Students are told that NASA is getting ready to send astronauts to Mars and needs to design a lander that will help the astronauts safely land on the surface of Mars. In this system, they apply Newton’s Third Law to design a solution--a lander--to a collision involving a spaceship and a stationary object, Mars.. Their task is to design a lander, using the provided materials (and maybe adding a few of their own) and their knowledge of Newton’s Third Law, that can safely land 2 ping pong balls/eggs/water balloons on the surface after being dropped from a designated height (like the top of a staircase or building). Students keep a design journal to document the tests they perform and the changes they make to their design. They also must document how they applied Newton’s Third Law in their design.
Finally, students are evaluated on their understanding of Newton’s Third Law by diagramming and designing a solution to the problems Gene Cernan had on his spacewalk.
Storyline Narrative 7.1.2
You found the secret message! Huzzah!
Every time Cernan exerted a force, it had the opposite reaction he had hoped for.
What is Newton’s Third Law of Motion and how does it affect the motion of an object?
Students watch a video about Astronaut Gene Cernan’s spacewalk, record and share their observations, and generate questions to answer as they continue to explore Newton’s Third Law in future episodes.
Students carry out investigations of Newton’s Third Law, diagramming the forces involved in each system.
Every force exerted on an object has an equal and opposite reaction force.
Does the mass of an object change the reaction force, especially if one object is more massive than they other?
The earth is so massive that when our mass is combined with the mass of the earth, the reaction forces has no affect on our motion. When we are not attached to the earth, the reaction force does have an affect on our motion.
How can Newton’s Third Law help us design solutions for safer collisions?
Students explain that very massive objects do have equal and opposite reactions, but it may not seem equal and opposite.
Students design a “Mars Rover Lander” that will safely deliver a golf ball/egg/water balloon to the ground.
Newton’s Third Law can be applied to design a solution to a problem involving the motion in a system to minimize the impact of the collision between two objects--in this case, the ground and the “lander”.