Newton's first law tells us that an object at rest will stay at rest

and an object with a constant velocity will keep having that constant velocity

unless it's affected by some type of net force

or you actually could say an object with constant velocity will stay having a constant velocity

unless it's affected by net force

because really this takes into consideration the situation where an object is at rest

you could just have a situation where the constant velocity is zero

So Newton's first law, you're gonna have your constant velocity it could be zero,

it's going to stay being that constant velocity unless it's affected, unless there's some net force

that acts on it, so that leads to the natural question:

How does a net force affect the constant velocity? or how does it affect the state of an object?

And that's what Newton's second law gives us.

So Newton's second law of motion.

And this one is maybe the most famous, they're all kind of famous

actually, I won't pick favorites here, but this one gives us the famous formula

Force is equal to Mass times Acceleration

And acceleration is a vector quantity and force is a vector quantity

and what it tells us, because we're saying okay, if you apply force

it might change that constant velocity

but how does it change that constant velocity?

We'll say I have a brick right here, and it is floating in space

Newton's second law tells us, and it's pretty nice for us that the laws of the universe,

or at least in the classical sense, before Einstein showed up,

the laws of the universe actually dealt with pretty simple mathematics

what it tells us is if you apply a net force on this side of the object

and we talk about net force because if you apply two forces that cancel out,

and have zero net force, then the object *won't* change it's constant velocity

if you have a net force applied to one side of this object,

then you're going to have a net acceleration going in the same direction

and what Newton's second law of motion tells us is that acceleration

is proportional to the force applied, or the force applied is proportional to that acceleration

and the constant of proportionality or to figure out what you have to multiply

the acceleration by to get the force, or what you have to divide the force by to get the acceleration

is called mass, that is an object's mass.

and I'll make a whole video on this, you should not confuse mass with weight

and I'll make a whole video on the difference between mass and weight

mass is a measure of how much stuff there is, now that we'll see in the future

there are other things that we don't normally consider "stuff" that does start to have mass

but for our classical or at least a first year physics course, you can really just imagine how much

"stuff" there is. Weight, as we'll see in a future video, is how much that stuff is being pulled down

by the force of gravity, so weight is a force, mass is telling you how much stuff there is.

And this is really neat that this formula is so simple, because, maybe we could have lived in a universe

where force is equal to mass squared times the square root of acceleration

which would have made all of our math much more complicated

but it's nice, it's just this constant proportionality over here

it's just this nice simple expression

and just to get our feet wet a little bit with the computations involved

in force, mass, and acceleration, let's say that I have a force

and the unit of force is a appropriately called the Newton.

So let's say I have a force of 10 Newtons, and just to be clear, a newton is the same thing

this is the same thing as 10 kilogram meters per second squared

and that's good that a Newton's the same thing as kilogram meters per second squared, because

that's exactly what you get on this side of the formula

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