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Newton's First and Second Laws

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The Flowers Are Still Standing
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The Flowers Are Still Standing

Credit: Robert Lopez
Source: CK-12 Foundation
License: CC BY-NC 3.0

An old magician’s trick is to take a table that is covered with various objects and to quickly remove the tablecloth without knocking over any of the objects. Whether they know it or not, this old magician’s trick demonstrates Newton’s 1st law.

Why it matters

  • Newton’s 1st law states that an object in motion stays in motion, while an object at rest stays at rest unless acted upon by an external force. 
  • Newton’s 1st law describes what is known a frame of reference. The law states that there must be at least one frame of reference relative to which the motion of an object (excluding external forces) is a straight line at a constant velocity.
  • Newton's 1st law is necessary because all of Newton’s other laws are based off of the first law. By starting from the statement that there must always be an initial reference frame, you are able to determine the acceleration on objects, reaction forces, torque and numerous other quantities. Using the links below you can see how the objects at rest (the flowers and plates) hold their position even though the tablecloth is quickly removed from underneath.
  • See the trick in action below: 

http://www.youtube.com/watch?v=cuG8sIiV8iQ

  • See the high-speed video of the Mythbusters experiment: 

http://dsc.discovery.com/tv-shows/mythbusters/videos/tablecloth-pull-high-speed-1.htm

Can You Apply It?

Using the information provided above, answer the following questions.

  1. In the videos above, you can clearly see that some of the objects moved and on one of the videos an object fell off the table. Why did this happen?
  2. How does a book sitting on your desk demonstrate Newton’s 1st law?
  3. Imagine you given an initial velocity v, to an ice cube that is sitting on a smooth. Initially the ice cube will have a constant velocity, but eventually it will come to a stop. Was Newton’s 1st law violated? Explain.

Image Attributions

  1. [1]^ Credit: Robert Lopez; Source: CK-12 Foundation; License: CC BY-NC 3.0

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