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ZingPath: Newton's First Law

Concept of Inertia

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Newton's First Law

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Lesson Focus

Concept of Inertia


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Learners interactively participate in experiments similar to those conducted by Galileo when developing the concept of inertia.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • (LO 1) State that when there is no net force acting upon an object, an object in motion will continue its straight-line motion.
  • (LO 2) State that when there is no net force acting upon an object, an object at rest will continue its state of rest.
  • (LO 3) Define inertia as the property of an object to resist a change in its motion, where the amount of inertia is directly related to the amount of mass.
  • (LO 4) Explain that when an object is placed on a set of two frictionless planes joined together in a “u” shape and released from some height on the left plane, it will continue moving forward until it reaches the same height on the right plane.
  • (LO 5) Explain Galileo’s experiments that helped him to develop the idea of inertia.

Everything You'll Have Covered

The concept of motion has evolved over the past two thousand years, and much of this change occurred as a result of the work done by Galileo and Newton.

Galileo could observe the effects of friction on the motion of objects, and sought to remove this force entirely. But, he could not entirely neglect the effects of friction, and so had to conduct thought experiments instead. He chose to set an object in motion by releasing it on an inclined plane. He noticed that when the amount of friction was small, an object would move down one plane, and reach a final height that was almost the same as the initial height. The object's speed would decrease as it moved up the second plane until it got back to its initial height. Galileo then concluded that in the absence of friction and a second plane, the object would continue moving with a constant velocity forever, because it would never reach its initial height. It is important to focus on the fact that an object will not change its velocity in the absence of a force, and it does not need a force in order to continue its motion as previously thought.

Newton later used Galileo's concept of motion to construct his own laws. In fact, is often called the Law of Inertia. Inertia is simply the resistance to a change in an object's motion, whether it is at rest or moving. In other words, the more massive the object, the greater its resistance to a change in its state of rest or motion.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts acceleration, constant velocity, force, gravity
Course Physics
Type of Tutorial Concept Development
Key Vocabulary acceleration, force, friction