Aristotle's Views on Motion

BHS -> Mr. Stanbrough -> Physics -> Mechanics -> Newton's Laws -> Newton's First Law -> this page

Introduction:

Aristotle's writings on motion are important for at least 2 reasons:

• They influenced scientific thought for almost two centuries.
  
• They provide a "common sense" framework that most people would agree "make sense."

Aristotle categorized motions as either "natural" motions or "violent" motions:

Natural Motion:

Any motion that an object does naturally - without being forced - was classified by Aristotle as a natural motion. Examples of natural motions include:

• A book lying at rest on a table naturally remains at rest.
  
  
• If you let go of a book it naturally falls toward the earth.
  
  
• Smoke naturally rises.
  
  
• The sun naturally rises in the east, crosses the sky, then sets in the west.

Violent Motion:

Aristotle classified any motion that required a force as a "violent motion". (He did not mean violent in the modern sense...) Examples of violent motion include:

• Pushing a book along a table.
  
  
• Lifting a book.

Summary:

Basically, Aristotle's view of motion is "it requires a force to make an object move in an unnatural" manner - or, more simply, "motion requires force".

After all, if you push a book, it moves. When you stop pushing, the book stops moving. (Not right away, of course, but, unless you push it, it gradually slows to a stop.) To keep a bicycle moving (on level ground) you have to keep pedaling. To keep a car moving, you have to keep the engine pushing it.

To most people, this is a very reasonable and "common sense" notion. There are only two problems with this idea:

1. It doesn't work, and
   
   
2. It isn't logical.

Read on...

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