Section 2 review
Newton’s three laws describe how motion is affected by forces. The first law says that, in the absence of a net force, an object at rest or in motion will continue to be in the identical state of rest or motion (that is, it will continue to have the same velocity). The second law states the relationship among net force, mass, and acceleration experienced by an object. The third law states that forces occur in pairs: For every “action” force (on a particular object), there is an equal but opposite “reaction” force operating at the same time, but on another object. Read the text aloud
friction, Newton’s first law of motion, Newton’s second law of motion, Newton’s third law of motion, reaction force

a= F m

Review problems and questions

  1. Which of Newton’s three laws of motion best applies to each statement?
    1. A 120 lb student sat on a stool, and the stool applied a 120 lb normal force to the student.
    2. The spacecraft cruised toward the North Star at a constant 500 m/s through the vacuum of interstellar space.
    3. Now that the moving van was full, its driver had to apply more force to reach highway speed before the on-ramp ended. Read the text aloud Show
  1. Two students are debating the meaning of Newton’s laws of motion.
    Arjun: “See that guy pushing the crate across the gym floor? He’s working hard, but the crate never speeds up. No acceleration! Newton’s second law can’t be right!”
    Buell: “I wonder. Newton’s second law has to do with net force, which is the total force you are left with after you add up all the forces pushing on something. I think there is another force at work.”
    Which student is correct, and why? Read the text aloud Show
  1. Rank the following objects by the magnitude of the net force that each experiences, from weakest to strongest:
    1. 150 g hockey puck that leaves a player’s stick at 30 m/s and enters the goal one second later at 29 m/s
    2. 20 g marble that has been dropped 1 m above the floor (and is still falling)
    3. golf ball that is tapped with a 0.5 N force while resting on a table Read the text aloud Show

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