Hi, it's Kaylee and this is the second video on forces about inertia
Galileo is one of the most famous scientist of all time
He lived a long time ago, but made some really important discoveries
one of these discoveries is this a
Body moving on a level surface
We'll continue in the same direction at a constant speed and less disturbed
Really this is just a fancy way of saying
If an object is moving with a constant velocity on flat ground
It will keep on moving forever until something stops it
The best way to think about that definition is a hockey puck on ice
Once the hockey player hits the puck
It will keep on gliding until a player hits it or even better it gets caught in the goals net
So this lesson is all about inertia, so let's define it
Inertia is an object's resistance
To change its motion
But this has two meanings like the hockey puck an object in motion want to stay in motion forever
But oppositely like a big rock at rest things that rest want to stay at rest forever
We can do two examples to show how the these properties of inertia show up in the real world
So let's do a quick lab at home
To prove that an object in motion wants to stay in motion
Fill a glass with water and grab a spoon you can pause the video here to grab supplies
Now that you have your supplies you're going to place the spoon in the glass and you're gonna stir the water quickly in the counterclockwise
direction
That means stirring it towards the left and you're gonna keep stirring for 10 seconds and after 10 seconds
You're gonna lift the spoon straight out of the glass
And now you're gonna watch the water
What does the water do after you remove to the spoon and you've stopped this the stirring?
So make your predictions about what will happen to the water after you stop
Stirring and then pause the video and give it a try
And if you don't want to do it yourself, I have a demo by a friend of mine that you can watch
So I hope you've made your predictions about what you think the water will do after you stopped stirring
So you've stirred the water for 10 seconds, and now you're gonna remove the spoon and if you're ready
You can watch my friend do this demo
Nice work
So the water in your cup should look something like this
after you've stopped stirring the water should still be spinning to the left in the direction that you stirred and
This is because the water has inertia and it wants to keep spinning and resist any change to its motion
like stopping
So great work doing an experiment on objects in motion that want to stay in motion
Now, let's try an experiment about an object at rest that wants to stay at rest
For the demo objects at rest want to stay at rest experiment you will need a dry empty cup an
Index card and a penny and you can pause the video here to collect your supplies
So now that you have your supplies you're going to set them up like this
You're gonna put the index card over the opening of the cup. So it lies flat and next
You're gonna place the penny on top of the index card. So it's about in the center of the cup and
Don't do it yet, but we are quickly going to pull the paper sideways out from under the penny and we're gonna make a prediction
What do you think will happen to the penny?
Take a minute to think about this and whatever you predict will be your
Hypothesis, do you think the penny will move sideways with the paper?
Now go ahead and pause the video and do this a few times pulling the paper quickly out from under the penny sideways
so
Take a few tries and do this here or if you want
I also have a video of my friend doing this demo that you can watch
Now if you've already done the experiment or you've already made your predictions you can keep watching to see the demo by my friend
So what happened to your penny did you like that slo-mo version of my friend doing the experiment
It was then easy to see that the penny went straight down into the cup
This is because the penny was at rest on top of the index card and the light being at rest and wanted to stay there
and when the paper was pulled the penny
resisted the change to its motion and it stayed at rest and
Even though the penny had inertia, it couldn't fight gravity. So it just fell straight down into the cup. Nice work
So now we're gonna play the forces and motion motion game
I'll play together first and then you can play on your own and we're gonna pay attention
To how much mass we push and see what happens to a cart once we stop pushing it
And see how an inertia acts in the real world. So let's play
So now we're in the forces in motion basics game on the plane the second game called motion
So the first thing that we need to clarify when we play this game
Is that the surface the ground that the skateboard is on has no
Friction. Okay, so just keep that in mind. There's no friction in this game
So the first thing I'm going to do is pick how much mass I'm gonna push around
So, um, let's try with the girl first. I'm gonna put her on top of the box and
I'm gonna get my speedometer out so I can keep track of if I'm
accelerating and
Let's see what happens if I start to push on her with only one Newton, so just barely any force
And I have to keep adding some. Oh
And she's barely starting to move. You see the speedometer barely start to go up. So she's accelerating. So I have
gotten an unbalanced force
But you see that it took me nine Newton's to get there and that's because she was at rest and she wanted to stay at
Rest, so we had to overcome that force
And let's see what happens if I push even more all the way up what's happening to my speedometer. Am I getting faster?
Yeah, it looks like her speed is increasing
So now we're moving we have an applied force so we have an unbalanced force and we have acceleration
Now what happens if I take away this applied force? I'm just gonna remove it back down to zero, huh?
So there's no more force applied and now what's happening
She's moving at a constant speed because she doesn't want to stop because of inertia
Look now her forces are balanced because there's no friction and she can just move at a constant speed forever
So now you can click the icon below and you can play around with this you can add all of the things you want to
Put the trashcan and the man and the president and whatever else on top of here and then you can inch it up by
50s by pressing the double arrow or by one Newton and you can see how much force it takes to overcome
The inertia of the object and then what happens when you stop applying the force?
Does it continue to move because an object in motion wants to stay in motion?
So play around with it and have fun and remember to always be clever