Lesson 1.9: Newton’s First Law of Motion

When the driver of a vehicle applies the brakes, a net force is applied to the vehicle. This is the force that opposes the vehicle’s forward motion. According to Newton’s second law of motion, the automobile undergoes a negative acceleration. However, what happens when the net force on a moving vehicle is in the direction of the vehicle’s forward motion? What happens when the net force is equal to zero? These are questions you will explore in this lesson. You will gain more insight into the concept of net force and Newton’s first law of motion.

• Read page 228 of the textbook and “Newton’s Second Law Applied to Speeding Up” at the top of page 229. Answer the questions as you encounter them.
  
  Check your answers with those in the “Practice Answers” in the online course.

After working with the applet “Newton’s Second Law,” you discovered factors that affect the rate at which a vehicle slows down. In the next activity you will use the same applet to study factors that affect acceleration in the positive direction. As in the previous activity in Lesson 1.8, sign convention will be used in the next activity. The positive direction will represent the direction of the vehicle’s initial velocity.

 

• Read page 231 of the textbook and the paragraph at the top of page 232.

Newton’s first law of motion explains why a curling rock continues to slide down the ice after it is thrown. The law also explains why a satellite remains in its orbit without the application of an external force to maintain its speed. But this law also has a downside, which is shown during a vehicle collision. Fortunately, vehicles have safety features that protect passengers from the aftermath of the first law. The next two activities show how the first law applies to vehicle safety.