Hi, it's Kaleigh this lesson is on Newton's first law
It will be important that you've already watched the videos
balanced and unbalanced forces and the video and interia
Sir Isaac Newton is a very famous scientist. He's the same guy
we named the SI unit of force after Newton and
He made some really big discoveries when we consider some of his most important
discoveries the laws of physics and
Sir Isaac Newton's first law of motion says
Everybody persist in its state of being at rest or of moving uniformly straight forward
Except insofar as it is compelled to change its state by force
impressed
say what I know this sounds really confusing but it's just a combination of our ideas of inertia and
unbalanced forces so we can rewrite this law as
Objects in motion stay in motion and objects at rest stay at rest unless acted on by an
unbalanced force
So that makes way more sense and now we can look at some examples of this law in the real world
Let's think about pushing a heavy box across some rough ground
So we're pushing really hard on the box. That's that blue arrow, but the box isn't moving yet. Why not?
Because there's a friction force that is just as strong as the force that we are applying to the box and
That means the forces are balanced and the box is at rest and we'll want to stay at rest because of inertia
But if we increase how much force we are pushing in the box
So that it's more than the amount of friction that's acting on the box
we can overrule the friction force and cause the force to be
Unbalanced so now what will happen to the box?
It will begin to accelerate that means a change in its velocity
So we've created an unbalanced force that will force the box to accelerate
The box at rest was unable to stay at rest
after being acted on by an unbalanced force
so let's try an example of an object in motion a
Ball is kicked at the top of this hill
Towards the bottom of the hill and notice that the hill flattens out at the bottom
Will the ball stopped rolling right when it gets to the flat part
Let's go ahead and kick the ball. We know that as the ball rolls down the hill it is gaining speed it is
Accelerating. So what happens when the ball reaches the flat part?
When the ball reaches the flat part of the field it will keep on rolling and this is because an object in motion
wants to stay in motion
And eventually the ball will come to a stop in the real world, but how or why
First it could run into something that could change its direction or stop its motion because of a force acting on it
but eventually the ball will come to rest because the friction of the grass will begin to slow the ball down and
the friction will become the strongest force acting on the ball and
Friction opposes the direction of motion. So the unbalanced force due to
Friction will be in the opposite direction of the balls motion causing the ball to stop
Now let's play another phet game
This is still in the forces in motion game, but this one has friction and we're going to be pushing a heavy box
And we'll see how much force we have to push to bring the box into motion from rest
We can change how much friction is present to see how it changes the motion of the box after we stop applying a force
Let's play
All right. So now we're in the Phet game forces and motion basics and we're on the third game friction
So here we have our box and it's on solid ground that has friction
So here we have a friction bar or we could say no friction. So it's ice or a
Lot of friction you can kind of see where the sand is added to the surface there
So we're gonna keep it about right in the middle for now just to practice
I'm gonna make sure I get my speedometer out and
I'm gonna try to push this heavy box. I'm gonna add some weight to it and
Let's see. I'm gonna add this girl here and let's give her a present
Summer we're investigating Newton's first law
So an object at rest
wants to stay at rest unless acted on by an unbalanced force an
Object in motion wants to stay in motion unless acted on by an unbalanced force
So, let's see right now. We have this big heavy object and it is at rest
Okay, so we're going to apply a force. We know that we have friction present
So we have to see how much force we need to apply to
override this friction
To it. So we are
Exerting an unbalanced force on this object so we can overcome the inertia and make this object accelerate. Okay, so I'm gonna add
Newton's by the 50 here so I'm gonna put 50 Newton's on
My friction force and my pushing force are equal
So I'm not moving yet a hundred Newton's not moving still not moving
200 Newtons we're still not moving. So forces are still balanced the object at rest still wants to stay at rest
300
350 and there he starts to go so our applied force our pushing force is
Unbalanced now, I just overcome the friction force and we can see our speedometer. Our heavy object is moving
so we have
acceleration here
amazing
so now we have an object in motion and we know that an object in motion wants to stay in motion unless acted on
By an unbalanced force. So what happens now if I take away my applied force
So I'm all the way down to you. Let's find zero so hard
And
Look at that she came to a stop because the friction force became the only force so it was unbalanced in the direction
opposite of the motion
So she came to a stop. How fun. So now let's try the same thing if we had no friction, right?
So we add her up here and we add our present
So now what's gonna happen if we only have to apply a small force right? Because we won't have any friction to overcome
So, let's see if I add
one Newton
To newtons, let's see how much force we have to apply to overcome her inertia
It looks like I'm already at two Newtons just barely accelerating
Three. I'm all still going right because there's no unbalanced force cuz there's no friction here
So I'm already in acting that unbalanced force for Newtons five six
Seven look at that, so I'm already going so let's give her some more so we can see this acceleration
So I'm gonna go up to you. Let's say 45
Newton so now we're really jammin she's got some acceleration here. We have no friction. So now what's gonna happen?
When an object in motion
Wants to stay in motion and there's no friction present and I take away all of that applied force
And she keeps moving now constant speed because now the forces are balanced
And she's off
So nice work, why don't you play around with this you can give it more friction or less friction
you can add a lot of mass or
Just double the boxes here and make sure you put your speedometer up so you can track when you are accelerating or not. And
Have fun with this explore Newton's first law and remember to always be clever