Bo: Hey, guys.
Billy: Hey, Bo.
Bobby: Hi, Bo.
♫ (lyrics) Flipping Physics ♫
Mr. P: Ladies and gentlepeople,
the bell has rung, therefore class has begun,
therefore you should be seated to your seat
ready and excited to learn about
uniformly accelerated motion.
Bo: Absolutely.
Bobby: Yes.
Billy: Oh boy.
Mr. P: Uniformly accelerated motion.
An object in UAM, or uniformly accelerated motion,
is an object that is moving with an acceleration
that is uniform, an acceleration that is constant,
an acceleration that is equal to a number and
that number does not change.
There are all sorts of objects that are
in uniformly accelerated motion, or UAM.
You could have, for example, a ball
rolling down an incline.
A person falling from a plane.
A bicycle on which you have applied the brakes.
A ball being dropped from the top of a ladder.
Or even a toy baby bottle, being released
from the bottom of a bath.
All of these are examples of objects
experiencing uniformly accelerated motion.
Yes, I know there is friction.
I know the incline isn't perfectly constant.
I know that the air exists.
I know that the water is actually going to apply
large drag force.
I also know that the brakes aren't going to
apply a perfectly constant braking force.
Therefore, none of these examples are perfectly
uniformly accelerated motion, but we can also
talk about the fact that we live in a non-constant
gravitational field, that the bike is actually
travelling on the surface of the planet, which is the
shape of a sphere, which means it's
not a euclidean surface.
We can also talk about the fact that travelling
you can spell with 1 or 2 "l's".
But none of this is stuff that we're gonna
talk about today because it's close enough.
All of these examples are very close to
uniformly accelerated motion, and therefore
we can consider it for the purposes of this class,
for all of them to be uniformly accelerated motion.
OK?
Bobby: Who is he talking to?
Bo: I don't know.
I didn't think anybody else was here.
Billy: Peanut gallery.
Have you guys never seen the peanut gallery?
Mr. P: Alright, moving on.
Here are the equations that describe an
object moving in uniformly accelerated motion.
There are 4 UAM equations.
I have written them right here and now I'm
going to walk my way through each one of the equations.
Velocity final is equal to velocity initial
plus the acceleration times the change in time.
Displacement is equal to velocity intial
times the change in time plus one half times the
acceleration times the change in time^2.
Velocity final^2 is equal to velocity initial^2 plus
2 times the acceleration times the displacement.
And the change in position is equal to one half times the
quantity of velocity final plus velocity initial
that can be multiplied by the change in time.
Bobby, there are 5 variables.
Could you please identify all 5 varibles
in these 4 equations?
Bobby: OK, let's see, there's velocity final
and velocity initial, acceleration, what else?
Change in time and delta X.
Bo: Words, not letters.
Bobby: Yeah, that's change in displacement.
Bo: Delta X is displacement, it's not
change in displacement.
Bobby: The last one is displacement, or
change in position.
Thanks, Bo.
Bo: You're welcome.
Mr. P: Yes, the 5 variables are velocity final,
velocity initial, acceleration, change in time,
and displacement, or delta X which means
the change in position because delta means
"change in" and X means "position".
Now, one thing that I do suggest when you use
the UAM equations is that you always use
base SI dimensions or meters and seconds.
Now, it's not actually mandatory, but I find
that students make many fewer mistakes
when they use meters and seconds
in the UAM equations.
Every once in awhile you don't have to,
but for the purposes of this class, we
are always going to use meters and seconds.
Now, the way it works is this.
If you know 3 out of the 5 UAM variables,
you can actually figure out
the other 2 unknown variables.
So, here's how it works.
Everybody ready?
Billy: Yeah.
Bobby: Sure.
Bo: Ready for what?
Mr. P: Class, there are how many
uniformly accelerated motion variables?
Billy: Uh...
Bobby: Ah...
Bo: 5.
Mr. P: OK, um, let's try that again.
Class, there are how many uniformly
accelerated motion variables?
Billy, Bobby, Bo: 5.
Mr. P: And there are how many UAM equations?
Billy, Bobby, Bo: 4.
Mr. P: And if you know how many of the variables?
Billy, Bobby, Bo: 3.
Mr. P: You could figure out the other?
Billy, Bobby, Bo: 2.
M. P: Which leaves you with 1?
Bobby: Uh?
Billy: Answer?
Mr. P: Not answer.
Turns out that because there are actually 2 unknown
variables, you could actually have more
than 1 answer, so what you are actually
left with is 1 happy physics student.
Bo: Ugh.
Billy: That's me.
Bobby: Yeah.
Mr. P: Alright, 1 more time.
There are how many UAM variables?
Billy, Bobby, Bo: 5.
Mr. P: And there are how many UAM equations?
Billy, Bobby, Bo: 4.
Mr. P: And if you know how many of the UAM variables?
Billy, Bobby, Bo: 3.
Mr. P: You could figure out the other?
Billy, Bobby, Bo: 2.
Mr. P: Which leads you with 1?
Billy, Bobby, Bo: Happy physics student.
Billy: Yeah.
Mr. P: That's right, 1 happy physics student.
In our next lecture, we're gonna go through
and work through a problem, an example problem
having to do with uniformly accelerated motion.
I hope you enjoyed learning with me today, class.
I enjoyed learning with you.
Voiceover: Lecture notes are available at Flippingphysics.com
Please enjoy lecture notes responsibly.