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LessonGrades 7 - 9

May the Force Be with You: Thrust

An animation shows a metal frame with five steel balls hanging from it in a line, each touching the balls next to it. As one of the balls is pulled away from the line and let go to be set into motion, it hits the next ball in line and causes a reaction to the subsequent other balls, resulting in the movement of the ball on the opposite end of the line. When this last ball falls back to the ball lineup, the energy is again transferred ball to ball, returning to the first ball. This process repeats and is an illustration of Newton’s third law of motion: for every action there is an equal and opposite reaction.Newton's cradle illustrating Newton's third law of motion.

Students study how propellers and jet turbines generate thrust. This lesson focuses on Isaac Newton's third law of motion for every action there is an equal and opposite reaction.

When designing airplanes, engineers apply Newton's third law of motion to determine how to best power the aircraft. The physical law states that for every action there is an equal and opposite reaction. Engineers design systems that create an action that in turn causes the airplane to move forward; this action is called thrust. To create thrust, they may use propellers, jets or rockets, and the heavier the airplane, the more thrust it requires to move.

After this lesson, students should be able to:

  • State that thrust is one of the four main forces acting on an airplane.
  • Identify that thrust is an example of Newton's third law of motion.
  • State Newton's third law of motion and provide real-world examples of the law.
  • Explain the difference in how jet engines create thrust compared to propeller engines.

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