07 May 2011

The Second Law

There is no need to throw your bowl
To prove that you are in control.
While Daddy watches from the door
Don't hurl your veggies toward the floor.

There is no need to make a case
Against the peas across your face
But if you decide you simply must
There's still no need to impart thrust.

Hold out one hand, release your grip
And watch the cheerios begin to slip
They'll tumble down and out of sight
With no display of strength or might

And when you wonder why they fall
One equation describes it all
The second law tells us the way
That F is equal to m times a

Where F is force, a word for weight
and a is the rate things accelerate
m is mass, of course, it's true
These laws also apply to you.

Newton said it was all of these
Not just apples falling from trees
But pureed pears, peaches and peas
And little girls with fresh skinned knees

Coins dropped into wishing wells
Or grains of sand pouring from shells
And raindrops falling from the sky
None of these knows how to fly

They only can move toward the ground
All these examples that we've found
I'll tell you now, though you may see
Force in this case is gravity.

But Newton did not specify
Since other forces can apply.
Wagons follow when pulled behind
That's force of a different kind.

And when you give your door a shove
Or throw around that ball you love
They may move fast, they may move slow
But it's a force that makes them go.

There are many things you can lift up:
Your baby brother, your spoon, your cup
But careful not to let them fall
Or gravity will find them all.

For gravity is here to stay
When other forces go away
As long as on Earth we walk or crawl
Things, when dropped, will always fall

And finally we would be remiss
If we failed to mention this
Another way the equation arranges:
F is the rate that momentum changes.

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