Module 3—Effects of Force on Velocity
Reflect and Connect
Knowing Newton’s laws, how could a child holding a physics textbook get off of a perfectly frictionless sheet of ice?
Try This
TR 4. Sketch a diagram to show how an action-reaction pair of forces could be used to move across a frictionless surface.
TR 5. Explain where the forces originate and how the child could minimize the time it takes to get off the frictionless sheet of ice.
TR 6. Compare and contrast the child's strategy for getting off the ice with the operating principles of a rocket engine. In your answer indicate what a rocket engine throws out that serves a similar purpose to the textbook used in the child’s strategy.
Module 3: Lesson 2 Assignment
Remember to submit the answers to D 1 and D 2 to your teacher as part of your Module 3: Lesson 2 Assignment.
Discuss
Go to page 141 of your textbook, and read "3-4 Decision-Making Analysis: The Airbag Debate.” Consider Newton’s third law, where every action has an equal and opposite reaction.
D 1. Answer question 3 of “Analysis” on page 141 of the textbook. Post your solution to the airbag issue to the discussion area, and respond to postings from at least two other students. If you wish to change your answers before submitting them to your teacher, do so.
D 2. Answer question 4 of “Analysis” on page 141 of the textbook. Post your proposed changes to the airbag design to the discussion area, and respond to postings from at least two other students. If you wish to change your answers before submitting them to your teacher, do so.
Reflect on the Big Picture
Each of the Reflect on the Big Picture sections in this module will ask you to consider the movement of people or goods. To help you reflect on your learning experience in this lesson, complete at least one of the following activities:
- Friction is both a help and a hindrance to transporting people and products. Without friction, it would be impossible to walk. But frictional forces make machines less efficient. Research how the Inuit solved the friction problem on their komatiks (sleds).
- Create a list of action-reaction pairs that you see when a child rides a bicycle. Choose at least two of the pairs, and make a textual, audio, or video presentation detailing how the reactive force helps the cyclist get to his or her destination.
Store your completed reflection in your Physics 20 course folder
Going Beyond
A block is resting on a table as illustrated. The normal force (N), which is the supporting force of the table, is equal in magnitude but opposite in direction to the force of gravity or the block’s weight (W). At first glance, this appears to be an application of Newton's third law. In fact, it is not.
Self-Check
SC 6. Explain why this illustration is not an example of Newton’s third law. (Hint: Think about what object the forces are acting on, and compare this to the forces acting on the two skaters that you studied earlier in the lesson.)
Self-Check Answer
SC 6. This is not an application of Newton’s third law because both of the forces are acting on the same object—the block. In any application of Newton’s third law, the action and reaction force must act on different objects.
Module 3: Lesson 2 Assignment
Remember to submit the Module 3: Lesson 2 Assignment to your teacher.