Aristotle lived and died over 2,000 years ago. That’s so far in the past that it’s before they invented last names — so he’s just Aristotle (single name like Cher or Prince). Then 1700 years later we have Isaac Newton (you know he is more modern because of the two names).
Yet here we are — still talking about these two humans in our introductory physics courses. Why do we care? It’s because they disagree with each other in their explanations of how forces make things move. And it turns out that most people agree with Aristotle’s ideas of physics — even though they are mostly wrong.
Let’s start with Aristotle since he built his ideas before Newton was even born. Aristotle was one of those famous Greek philosophers — and that means he was a philosopher and not a scientist? What’s the difference? Well, a scientists builds models based on experimental evidence and a Greek philosopher just makes some starting assumptions.
With that in mind, Aristotle came up with some “rules” about the way nature works. There’s a bunch of stuff that he attempted to describe, but let’s just look at a simple example. Suppose a block sits on a table and someone pushes it from the side (just like the picture at the top). When the block is pushed, it moves at a seemingly constant speed. When the person stops pushing the block, it stops. That’s pretty straightforward.
But why? Why does the block do this? Aristotle uses the following force-motion rule (I’m going to paraphrase this since I can’t write in Greek).
The natural state of motion for the block is to be at rest. If you leave it alone, it will be at rest. So, when you exert a force on the block with a finger, it moves. When you stopping pushing on it, it returns to its natural state — yes, it goes back to being at rest. Physics is simple.
Even without doing an experiment, Aristotle’s ideas seem to be quite reasonable. Right? I mean, we see this all the time. You push something it moves, you stop pushing and it stops. Most people agree with Aristotle’s physics.
Just to match Newton, we can write this as the following:
Aristotle’s 1st Law of Motion: An object stays at rest unless acted on by a force.