In high school I had to memorize the definition of inertia. It was something along the lines of: an object in motion will remain in motion and an object at rest will remain at rest until acted on by another force.
This principle applies to so many areas of my life.
I have found that if I get up and get going first thing in the morning, I accomplish a lot that day. I get started and keep moving. But if I get up and I don't get going--like perhaps getting on my computer too early, or sit around talking to kids too long--I just seem to stay at rest. I suspect this is true for most people.
Children can act as a force that changes my current state of motion. If I am at rest and hear certain things, like crying, something breaking, or quite a few other things actually, I will jump up pretty quickly. If I am in motion and a child needs comfort, I will find myself at rest holding that child.
And my will power can change my state of motion too. This is an important principle I have finally figured out. I can be busy and needing rest and tell myself, "Stop!" and then get some rest. When I do this, I find I'm better able to get things done later. Duh. It shouldn't have taken me so long to learn this. And equally important is that when I find myself resting too much and not getting things done, I can tell myself, "Time to get moving." and get up and get going. And I feel good when I'm running around getting things done.
So there's one law of physics I'm finally mastering. If only my children could figure out the one about how no two objects can occupy the same place at the same time (like my lap perhaps) and then if there isn't one already, there should be one about how no one can be in two places at once.