Early thoughts

Introduction

Our thoughts about mechanics, or the study of how objects move and interact, have changed over the centuries. During the time of the ancient Greeks, philosophers like Aristotle thought that in order for an object to be in motion, it must have a constant force (an action that causes an object to accelerate or change shape) applied to it. Otherwise, an object's natural tendency was to stay motionless. It was believed that any object in motion had a force of some kind behind it, regardless of whether that object was accelerating or moving at a constant velocity.

Aristotle

Living objects, such as human beings and animals, moved using voluntary motion, according to Aristotle. For objects such as arrows travelling through the air, Aristotle believed that motion was perpetuated (made to continue) by the force of air rushing in behind to fill the vacuum created by the object's movement. Any motion that occurred because of a force was called forced motion. Aristotle also believed that objects fell to the ground because the ground was their 'natural place'. He called falling natural motion. Aristotle's theories were false, although they were very popular at the time.

See Image 1

John Philoponus

In the 6th century AD, a scientist named John Philoponus suggested that once an object was put in motion, it gained a property called impetus which kept an object moving when it was in motion. Eventually, this impetus would run out, and the object would stop moving. At the time, this theory was not particularly popular, although it enjoyed a brief revival during the 14th and 15th centuries by scientists like William of Occam and Nicolas Oresme.

Galileo Galilei

In the 16th and 17th centuries, a scientist named Galileo Galilei studied the motion of various objects and came to a new conclusion. When he rolled balls of different sizes down inclined planes, he discovered that they accelerated at the same rate. This is because gravity acts upon them at the same rate. He also noticed objects tended to stay at the same velocity unless another force acted upon them to change that velocity. He called this property inertia.

See Image 2

Isaac Newton

Isaac Newton was a scientist whose theories strongly influence our understanding of mechanics today. In the 17th century, Newton created three laws that describe the motion found in the universe:

1. Objects in motion tend to stay in motion unless acted upon by an unbalanced force. Objects at rest also tend to stay at rest unless acted upon by an unbalanced force.
2. The acceleration of an object is directly proportional to the force applied to it and inversely proportional to its mass.
3. For every action, there is an equal and opposite reaction.

The effects of Newton's Laws of Motion will be discussed later in this topic.