Home School Life Journal

Home School Life Journal ................................................................................................................painting by Katie Bergenholtz

Elementary and Middle School Physical Science: Mechanics in Motion: Newton's First Law of Motion {Inertia}

Newton's First Law of Motion is the law of inertia, or the fact that something at rest prefers to stay at rest unless something forces it to move, and something in motion prefers to stay in motion unless something forces it to stop moving.

Inertia Demonstration 1
Stack 5 pennies in a neat stack on a table. Lay another penny on the table near the stack. With a lot of force, slide the penny into the stack.

Only the bottom coin of the stack should have moved. It was forced to move by the moving penny which hit it. The other coins resisted movement because they prefer to stay at rest.

Inertia Demonstration 2
Place a glass of water on a table and place an index card on top of the glass of water. Next, carefully place a stack of 5 pennies on top of the index card. Now, yank the card out.

Did you notice the stack of coins was suspended in midair for a moment? That is inertia.

Now, set up the experiment again, but this time grasp the card with your fingers and slowly  put it away from the glass, keeping the card level as you pull it away. 

This time the coins should have traveled with the card instead of falling into the glass. The coin had a certain amount of inertia sitting at rest. In order to overcome this inertia, a strong enough force would have to be applied. In the first part of this demonstration, friction was not allowed to work long enough to overcome the coin's inertia, so the coin did not move with the card. In the second part of the demonstration, however, friction was allowed to work long enough to overcome the coin's inertia and the coin moved with the card.*

sources and resources:

  • Exploring Creation with Chemistry and Physics, Jeannie Fulbright
  • Exploring Creation with Physical Science, Jay Wile*


  1. Great ways to show first law in action! Physics can be fun!

  2. I love this! I'm thinking of doing physics after we do chemistry next year. We'll see...


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