# how is inertia involved in Newton's first law?

Newton's first law says about two things when no force is there.

1)State of rest. 2) state of uniform motion

'State of rest' means to us as 'speed is zero' and 'state of uniform motion' means to us 'speed is constant.

But Newton did not mean that. What he meant is the quantity ' momentum'

To him
'State of rest' meant 'momentum is zero'and 'state of uniform motion' meant 'momentum is constant'

Another name for momentum is inertia. Therfore, we say Newton's first law is about inertia.

But momentum is the mass x velocity(speed).
But in practice, many of the times we donot come across bodies that change their mass due to the force. Hence we perceive by Newtons first law the earlier meaning,''State of rest' means 'speed is zero' and 'state of uniform motion' means 'speed is constant. and Inertia as mass.
Newton's First Law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. It may be seen as a statement about inertia, that objects will remain in their state of motion unless a force acts to change the motion. Any change in motion involves an acceleration, and then Newton's Second Law applies; in fact, the First Law is just a special case of the Second Law for which the net external force is zero.

Newton's First Law contains implications about the fundamental symmetry of the universe in that a state of motion in a straight line must be just as 'natural' as being at rest. If an object is at rest in one frame of reference, it will appear to be moving in a straight line to an observer in a reference frame which is moving by the object. There is no way to say which reference frame is 'special', so all constant velocity reference frames must be equivalent.
Index

Mass on string example.

Newton's laws concepts.
The principle of inertia is one of the fundamental laws of classical physics which are used to describe the motion of matter and how it is affected by applied forces. The concept of inertia is today most commonly defined using Isaac Newton's First Law of Motion, which states:

Every body perseveres in its state of being at rest or of moving uniformly straight ahead, except insofar as it is compelled to change its state by forces impressed. [Cohen & Whitman 1999 translation]

It should be emphasised that 'inertia' is a scientific principle, and thus not quantifiable.

In common usage, people may also use the term 'inertia' to refer qualitatively to an object's momentum or its 'amount of resistance to change in velocity' (its mass), depending on context (e.g. 'this object has a lot of inertia'). The term 'inertia' is more properly understood as a shorthand for 'the principle of inertia as described by Newton in his First Law'.
Inertia is the property of mass that resists change to its movement.

Another way to describe inertia is 'an object at rest tends to remain at rest, and an object in motion tends to remain in motion'.

This is Newtons first law. See the link below for more details.

THE HAT LAW (beeep! beeep! Move it Hat Guy!)
THE YOU BIG BULLY LAW (try & knock me down)
THE HELP I'M A BUG LAW (SPLAT! *Help, I'm a bug!*)

Your question rocks because all you hear from books and teachers is (use Peanuts TV show teacher voice here)

'bwah bwah INERTIA bwah bwah tends to remain in motion bwah bwah equal and opposite reaction bwah bwah bwah'

I think this is because they do not really understand it.

You know who understands this stuff by the seat of their pants? Bikers! Harley, Suzuki, Honda, you name it, they totally get it.

But you have asked what is so QUESTION NUMBER ONE in physics.

Here's a way to remember and understand through a totally whack story.

It took a super-genius, I mean way smarter than Einstein, to figure it out. A good old farm boy, astrologer, magician & alchemist, religious fanatic, mathematician and all around kook. Yes sirree, Sir Isaac Newton.

Well we all know what a force is, it is a sort of push or pull -- think of it as something that changes or *tries to change* the motion of stuff.

Newton first figured out that if you leave a thing alone, or if the pushes and pulls on it cancel out, then it will sit there like a lump. This is called INERTIA, Like those drivers wearing hats, and like sit there after the light has already turned green two minutes ago.

Or else a thing will keep moving in the same straight line direction and speed like those drivers wearing hats who go 40 mph on the expressway with their turn signal blinking on and on. This is also INERTIA and is also known as 'THE HAT LAW'.

It comes from the Latin words meaning artless -- not like painting 'art' but an art like a skill. LIke if you ask your buddy to help you change your tire and he is like 'dude, I would but I so do not know how.. I am artless.. sorry man'

All was well until he noticed that things move faster in an amount equal to how much you bully them or push them around. Twice the force, twice the fasterness and fasterness (also known as acceleration). This is called the 'YOU BIG BULLY LAW'.

Then he discovered a fly in the ointment. His HAT and BULLY laws didn't really explain all that much. Something was gumming up this beautiful theory. We call it MASS and it is still an unknown mystery as to what it really is. So we vaguely call it the amount of stuff or matter in a thing.

So he found out that for a certain force the faster-isity (acceleration) is cut in half if you double the mass. The bully has to push twice as hard to fasterize two little kids. So he was like 'I'll just add that in, and all will be cool'. The 'YOU BIG BULLY LAW' and 'THE HAT LAW' totally did it all. Let's hear it, big-time: Boo Yah!

But then Newton had a road accident. He was gunning his Harley over London bridge at like 250 when a bug hit him in the mouth and knocked out one of his wooden teeth. He was all 'Why am I so in pain?'. And the bug as it squooshed said 'Help! I'm a bug!'

So spitting out the splinters of his wooden tooth and the splattered bug, he had this revelation. He realized that because he was moving so fast, and the bug slowed down so fast, that even a miniscule mass like a bug was like taking a hammer to his tooth.

He noticed that the force was equal to the mass of the bug times the speed of impact all happening in a brief moment.

Since Newton spoke Latin (he was the love child of Joe Newton and an Italian governess) he wrote 'Fastus buggus ina momentum hurtus like crazy.' Today we call this 'momentum' (really) It is just 'mass times speed' or 'force times a small moment of time'.

And he realized that the bug smashed up his tooth, but also that the bug was squashed (like a bug) because they were trading off the EXACT same amount of momentum.

The force on the tooth by the bug in the moment of time was PRECISELY equal to the smacko-ing the tooth used to stop the bug dead.

He said 'Hey, like he broke my tooth, but I killed him soooo dead!' He did the math and found that the force of the bug on the tooth was equal to the force of the tooth on the bug!

No way did the two equal forces cancel, after all, his tooth was hammered to splinters, and the bug was flattened. They were equal and opposite, but since one was on the tooth, and the other force was on the bug they did serious damage! Today we call this the 'HELP I'M A BUG' law.

Now our man 'Zack was all set. He wrote down his three laws:

THE HAT LAW (beeep! beeep! Move it Hat Guy!)
THE YOU BIG BULLY LAW (betcha can't knock me and my brother down)
and
THE HELP I'M A BUG LAW (OUCH!*Help, I'm a bug!*)

He got so totally wealthy from this that he ran for political office and became head of the Mint and happily pottered away the rest of his life trying to turn lead into gold (really!). Until his bladder burst and killed him.
I can't even spell inertia. Wait I just did.
idontno