Mr. Croft's Home Page

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Playing Card Demo

Place a playing card over the top of a drinking glass.

 Put a coin on top of playing card.

 If you flick the card with your finger the card will fly out from under the coin... Inertia




Raw or Boiled?


I have 2 eggs.  One is raw and the other is boiled.  How can I tell them apart without cracking them open?

Spin the eggs.  The hard boiled egg will spin easily but the raw egg will not spin as well because of inertia.  The yolk is slower moving.



Hanging Books


Suspend two identical books by yarn from the ceiling. Tie yarn below the books too.  I can break the yarn above or below the books.  By pulling on the yarn slowly the book will begin to move and the yarn should break above the book.  If I yank quickly on the yarn it should break below the book.   This one is a little tricky and I would encourage you to practice.


Inertia Trick

Cut rings from a large plastic container.  Place the ring on an empty drinking glass and place a coin on top of the ring. 

Hit the inside of the ring and the coin will drop into the glass. 

Hit the outside of the ring and the coin will fly across the room.


Wine Glass Inertia Demo

 Materials for Inertia Demo
2 glasses I picked up a couple of wine glasses at the local dollar store. I used my wife's crystal once... Fill the glasses with water.

2 dowels. One thin (5/16 inch) and the other thick (5/6 inch).


Place  two wine glasses filled with water on two matching desks or chairs.  Carefully balance a small dowel on the edges of the two glasses.  You may have to take some time to adjust the distance so that the edges of the dowel do not overlap the edges of the glasses by too much. I face the class when doing this demo and make sure that no one is standing on either end of the small dowel.  I usually talk a little about Sir Isaac and his First Law of Motion.  I always take 3 practice swings with the students counting




Strike the small dowel as quickly as you can in the center.  I have not lost a glass or a drop of water yet.... but I would practice this at home first.




          Isaac Newton's First Law of Motion

An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.




Web Sites


Comeback Can

Inertia Experiments  Rahi and Abokor  Fayetteville State University

More Inertia Experiments   Institute of Physics

Physics Classroom tutorial   (Has animation)


Tide 2     Kelly Ripa's commercial with classic  inertia demo.


Thank you for visiting the Inertia Page.

I last checked this page on March 9  2010

We have had visits from Glendale Oregon, Oxford Mississippi,  Toronto Ontario Athens Georgia,  Lufkin Texas,  Barrie Ontario,  the Philippines, Charlotte North Carolina, Owosso Michigan, and Jupiter Florida

Please take time to post a note on the  Inertia Wall


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Last updated: 01/02/13.