What are some good examples of "Newtons' Law?"

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ophelious | High School Teacher | (Level 1) Educator

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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.

element-water's profile pic

element-water | Student, Grade 6 | (Level 1) Salutatorian

Posted on

Newton's first law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by a external force. An example of this is a mass on a string. The string provides the centripetal force needed to move the ball in a circle. The straight line motion in the absence of the force is an example of Newton's first law.

 

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