Hello, [dodge ball swooshes by] fellow scientists! [bounce] It's Justin here again, [swoosh]
and [swoosh] welcome back to — Woah! [laughs nervously] That was coming at
me with some force, huh? [swoosh] Whew. [laughs] OK, I'm going to be honest with you. I know we got
to do science today, but I really wanted to play some dodgeball! So, uh – woah!
[dodge ball continues swooshing back and forth] ...Here we are.
Hey, I've got an idea. Maybe we can use what we're gonna learn today
about forces and motion to help me win this game of DODGE ball.
And quickly. Hmm...
By the end of this lesson (slash extremely competitive dodgeball game), you
will be able to explain what force and motion are and their relationship to each other. Plus, you'll
be able to describe the relationships between force, mass, and acceleration. Let's get into it!
So, what is a force? In physics, a force is any kind of push or pull on an object.
For instance, when I throw this dodgeball, I am exerting a force onto it. I'm pushing it,
and that causes the ball to move away from me. And if I were to pick the ball back up, I would
also be exerting a force on it. This time, I'm pulling it, which causes it to move towards me.
Every day, we are constantly exerting forces onto objects and experiencing forces ourselves. As a
matter of fact, every single thing on this planet is constantly experiencing one very important
force: the pull of gravity. Forces can either be balanced or unbalanced, which is what determines
if an object is moving or still. For example, let's take a look at this dodgeball just sitting
on a table. We know that it's under the force of gravity, which pulls objects towards the Earth.
So why isn't it plummeting to the ground?
Well, the table's holding it up, of course. The table is pushing back against the dodgeball with
a force equal to the pull of gravity. The forces here are all balanced, so the dodgeball stays put.
What kinds of balanced forces do you see around you right now?
Pause the video here to write down what you can see in your guided notes.
But what if the forces were unbalanced? If we remove the table,
there would be no force to balance the force of gravity acting on the ball,
so the ball would be set in motion, plummeting towards the Earth.
So, unbalanced forces are what cause motion. But what is motion exactly? Well, motion is a change
in an object's position. For example, if I were to start on this side of the room and then walk
— boop, boop, boop, boop, boop —
over to this side of the room, I have changed my position, so I've experienced motion.
Are there any objects in motion that you could see around you right now?
Pause the video here and write down what you can see in your guided notes.
We can describe an object's motion by observing its speed and direction. That's called an
object's velocity. When an object's velocity changes, that change is called acceleration.
For example, imagine a car driving down a highway. It's traveling at
a certain speed in one direction. That's its velocity. If the driver changes the
car's velocity by slowing down or speeding up, that change is the car's acceleration.
So, a force is any push or pull on an object, and forces are what cause motion,
or changes in an object's position. Great! But how does that help me with my dodgeball game? Well,
to answer that question, we're going to need to turn to someone really cool for help. You
might have heard of him. His name is Sir Isaac Newton. Over 300 years ago, Newton observed
some fundamental truths about the relationships between forces and motion. Today we call these
truths Newton's Laws of Motion. Let's see how Newton's three laws can help me with my dodgeball.
Newton's first law states that an object at rest will stay at rest and an object in motion will
stay in motion unless an outside force is acted upon it. Cool! So, that means I now know that a
dodgeball that is not moving will continue to not move until I exert a force on it,
and once I do, then the ball will continue to move until another outside force acts upon
it — something like the pull of gravity or another player catching the ball. This additional outside
force will cause all of the forces acting on the ball to balance out, returning it to stillness.
So that's cool and all, but how am I going to figure out how much force I need to get the right
velocity, you know? Well, Newton's second law of motion can help us with that. Newton's second law
states that the force acted upon an object is equal to its mass times its acceleration.
Simply put, the more force I put into an object, the more it will accelerate.
Ah... So the more force I put into my throw, the faster the dodgeball will go,
and that'll make it harder to dodge! Awesome! That's really useful. Now, you might be wondering,
what about that mass part of the equation? Well, Newton's second law also tells us that
the more mass an object has, the more force has to be applied to it to get it to move.
So, uh... hmm... While this gigantic dodgeball I made might seem like it'd give me the edge,
I now doubt that I'd be able to apply enough force to it to get it moving at a reasonable speed.
It's, uh, it's "Dodgeball," not "Slowly Move Out of the Way Ball," so we're gonna [strains]
get it out of here. Sorry! [strains] There you go.
Can you see any objects around you that would require a lot of force to move?
Pause the video here and write down your examples in your guided notes.
OK. So, so far it looks like throwing a regular-sized dodgeball with more force to give
it more acceleration is the best way to go, but what else can Newton teach us that'll help me out?
Newton's third law of motion states that for every action, there is an equal and opposite reaction.
This means that when my ball hits an opponent and exerts a force on them,
my opponent will exert an equal force back on the ball without even trying.
This is what will cause the ball to stop and change direction. If I keep Newton's
third law in mind, I'll be able to see why balls bounce back to my side of the court.
Let's review everything we've learned about force and motion so I can use it to conquer this game.
A force is any push or pull on an object. Forces are what cause motion, or a change in an
object's position. Velocity and acceleration are measurements of an object's motion. And finally,
Newton's three laws of motion each describe the relationship between force and motion.
To learn more about forces in motion, be sure to check out the activities and
practice questions that go with this lesson. And as for me, I think I'm ready to become
the MVP of this game. [triumphant laugh] I know exactly how much force to put into my
throw to get the velocity I want, the mass of the ball is perfect, I have everything —
Oof!
Aw!
Oh...!
Ow...
OK... OK, it looks like the other team was studying forces in motion too.
Great, great. [ball dribbles away on the ground] [sighs]
Well, until next round, remember: Science is all around us. See you next time!
[groans] [laughs it off]