Teaching Newton’s second law

I’ve been teaching Newton’s second law to my 6th graders, and I’m really surprised at how the textbooks try to do the math. When I learned it (back before dirt), I learned f = ma (force is mass times acceleration). Our textbook says a = f/m (acceleration is force divided by mass). But I haven’t seen a textbook use this:

Newton's Second Law

With this, all you do is plug in what you know, and it will show you how to get what you’re missing. For example, if you have force and acceleration, you fill them in, and you have force divided by acceleration. That gives you mass.

You can also think about like this: I want to get the force, so I cover up the f. I’m left with mass times acceleration. Or I want to get acceleration, so I cover up the a. I’m left with f over m.

Now, instead of having to remember 3 formulas (f=ma, m=f/a, a=f/m), I just have to remember this one thing that gives me the 3 formulas. All I really need to remember is that force goes on top (because multiplication is commutative).


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