Motion and Forces: Newton's First Law of Motion

By Accessible Science on Nov 07, 2014

The activity described below gets everyone’s attention! Students with a visual impairment benefit from a chance to feel the weight of the various items placed on the tablecloth, as well as a chance to examine the table before and after the table cloth is pulled.
 

Vocabulary

Inertia – the tendency of an object to keep its motion
 

Inertia

Place a book on your desk. Does the book move? Unless you push the book, it will stay put just the way you left it. Imagine a spacecraft moving through space. When the engines are turned off the spacecraft will coast through space at the same speed and in the same direction. The book and spacecraft have inertia. Because of inertia, an object at rest rends to stay at rest. An object in motion tends to keep moving at a constant speed in a straight line.

book on a desk

 

Newton's First Law

Newton’s first law of motion explains how inertia affects moving and nonmoving objects. Newton’s first law states that an object will remain at rest or move at a constant speed in a straight line unless it is acted on by an unbalanced force. According to Newton’s first law, an unbalanced force is needed to move the book on your desk. You could supply the force by pushing the book. An unbalanced force is needed to change the speed or direction of the spacecraft. This force could be supplied by the spacecraft’s engine.
 

Effects of Interia

You can see the effects of inertia everywhere. In baseball, for example, to overcome inertia a base runner has to “round” the bases instead of making sharp turns. As a more familiar example of inertia, think about riding in a car. You and the car have inertia. If the car comes to a sudden stop, your body tends to keep moving forward. When the car starts moving again, your body tends to stay at rest. You move forward because the car seat exerts an unbalanced force on your body.

 

Materials

  • Table cloth
  • 2 unbreakable plates
  • 2 unbreakable cups drawing of a place setting
  • 2 forks, spoons, napkins
  • The heavier the cups and plates, the better it works A textbook
 

Procedure

  1. Start with the table cloth on a table or desk.
  2. Set the table as if for dinner.
  3. Notice the difference in mass of each object. The book has the most mass and the napkin has the least.
  4. Try the magician’s trick of grabbing the edges of the table cloth and then quickly jerk it out from under the items on the table.
  5. Hopefully you’ll notice that the napkin flew off (less inertia), and things like the silverware, plates and book stayed put.

 

Questions and Conclusions

  1. In space, a spacecraft with its engines turned off will move with constant speed in the same __.
  2. A book will not move by itself because it has __.
  3. A book will remain at rest unless it is acted on by an __ force.
  4. When a car stops suddenly, your body tends to keep moving __.
  5. Newton’s first law explains how inertia affects moving and __ objects.
 

NGSS Standards:

Motion and Forces:
The motion of an object is determined by the sum of the forces acting on it; if the total force on the object is not zero, its motion will change. The greater the mass of the object, the greater the force needed to achieve the same change in motion. For any given object, a larger force causes a larger change in motion. (MS-PS2-2)
 
PS2.A: Forces and motion: The role of the mass of an object must be qualitatively accounted for in any change of motion due to the application of a force. (Grades 6-8)
 

Article and activity adapted from Concepts and Challenges: Physical Science, Fourth Edition. Parsippany, NJ: Globe Fearon Inc., Pearson Learning Group, 2009, pages 280 to 281.

 
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