Robin Ford, April 2018

 Setting the scene

What exactly Newton wrote in his laws of mechanics is a regular topic in books and blogs. Because you have chosen to read this you are probably familiar with the argument; maybe you have posted your views on your own blog?

So why am I adding to it all?

I’m offering a jingle that encapsulates the story. Here it is.

The jingle

Newton did not say
F = ma
The treatise that he sent’em
Linked impulse and momentum

Explanation

If this idea is new to you, you could follow this up with web-searches, but to save you time here’s a summary.

Newton’s second law is often expressed as

Force = (mass)x(acceleration)

Where the acceleration is in the same direction as the force.

Or

 F = ma

Where the underline means a vector quantity.

What Newton actually wrote (in Latin) is translated something like this:

 The change in the quantity of motion is equal to the motive force impressed and takes place in the line of the motive force impressed.

In modern terms this becomes

 Change in momentum = impulse

Or

 (mv₂-mv₁) = Ft

And the story is complete.