Okay...so we're talking about Newton's Three Laws of
Motion, I presume?
As previously answered by
element-water, the first law reads like
this:
I. Every object in a state of uniform
motion tends to remain in that state of motion unless an external force is applied to
it.
What does that
mean, exactly? Things want to keep moving in the direction that they are going, and at
the speed they are going, unless something monkeys with them. For example, roll a
bowling ball and it wants to keep going straight (unless you've given it a wicked
curve!) Out in space it would keep going straight, at that speed, for a long time.
Here on Earth, gravity, friction, imperfections in the wood of the lane, and (of
course!) hitting the pins would all mess with that motion. So, Newton is saying that
things will keep going in a straight direction, at the same speed, unless some outside
force intervenes. Remember, the outside force could be something as simple as
wind-resistance!
This also has to do with objects that
aren't moving at all. They want to stay put. Think what would happen if you put the
bowling ball at the end of the lane and just set it there. The ball would want to stay
put, unless the floor was out of balance or something. This force is called
inertia.
Basically, Things that are
moving want to keep doing so, and things that aren't just stay lazy and want to be
still.
II. The relationship between an
object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and
force are vectors (as indicated by their symbols being displayed in slant bold font); in
this law the direction of the force vector is the same as the direction of the
acceleration vector.
Numero Two-O is a
little harder to get a handle on. It has to do with applying force to an object to move
it. Technically it's acceleration. The gist behind the
second law is that a little force to a big object (meaning mass-wise) won't budge it
much, while a big force to a little object (again, mass-wise) will send it flying. The
more massive an object is, the more force is required to overcome its inertia. Again
with the stupid bowling ball...there are reasons why they come in so many different
weights depending on how strong you are. A heavier ball needs a stronger arm to
accelerate it.
III. For every action there is an equal
and opposite
reaction.
The
third one isn't too hard to get, but the examples are a little harder to wrap the ol'
noodle around. One way to think of this is sort of like what you see when playing pool
sometimes. Have you ever noticed that when people "break" in pool the cue-ball often
sort of bounces back after hitting the balls? Of think of a bird...how does a bird's
wing, pushing down on the air during a flap, make the bird go up? Why doesn't it just
make the air go down? Because of Newton's third law. Pushing down on the air makes
the air push up.
Maybe an easier way to see this law at
work is to watch a rocket. The engine of the rocket pushes down on the ground, and the
ground pushes back against it (thus sending it up into the air.) There is an equal
reaction to the force of the rocket engine, and it is in the opposite direction (rocket
pushes down, it is pushed up in return.)
Anyhow, that's
about it for the three laws.
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