WEBVTT

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Hi.

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Welcome back.

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In this video, we're going
to talk about biomechanics.

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In the last video, we
talked about anatomy,

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which is that study of
structures of your body.

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Now, we're going to apply
mechanics to that biology

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and talk about
how the body moves

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and what words we
use to describe that.

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Do you have a
favourite definition?

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For biomechanics?

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Yeah.

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Well it is a combination of
biology and mechanics, I guess.

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Yeah, exactly.

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So it's a pretty
interdisciplinary field--

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you've got physics thrown
in there, some biology,

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some medicine--

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so you're going to
use a lot of words

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that you may have
seen in other classes.

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What I like to do when I
talk about biomechanics

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is to first break it
down into two parts.

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OK, so the first is kinematics,
and that's what you can see--

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your angles, the positions.

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And then the next is the
kinetics, what you can't see,

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what's going on underneath
body movement-- forces

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like good old gravity.

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So, Victor, do you have
a favourite movement?

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Jumping.

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Jumping.

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All right, so
Victor jumps, right?

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He jumped.

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So in the last video,
we talked about words

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to use to describe what
moved-- anterior, posterior,

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flexion, extension.

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Now, we're going to talk about
how we actually analyse these.

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There's different ways to
describe Victor's jump, itself.

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We could talk about
how high he jumped.

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We could also talk about
how good his jump was.

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When we quantify things, those--

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or we could qualify things.

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So how would you rate
yourself from a qualification

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of your jump?

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Mediocre.

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Yeah, all right.

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Do you know how high you jumped?

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20 centimetres?

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OK, so those are just difference
in quantitative variables

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and quantitative variables.

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Now if we'd talk about,
say, kinematics--

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you saw that his foot
position changed.

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We could say if he
jumped 20 centimetres,

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his toe moved 20 centimetres.

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We could also talk about angles,
because we have both vector

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and scalar options.

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Could you give me a
difference between your jump,

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in vector and scalar?

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Vector and scalar could
be the speed of the jump--

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Yeah, so if he jumped, say,
at 3 metres per second,

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that was a speed.

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If we then make it
a vector, we say

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he jumped 3 metres per second
in that upwards direction.

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So vectors have magnitude--
or what we call a direction--

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to it.

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So in biomechanics, you'll see
a lot more vector quantities

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because we talk about how
something got from one place

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to another, not just
general scalar quantities.

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Another thing we like to do
is talk about the difference

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between linear and angular.

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So when you watch
Victor jump, you'll

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see that his body
moves linearly up.

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But his knees, because
they're bending and rotating,

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they're actually moving
angularly in that knee joint.

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So they're moving about the knee
angle, in that rotation term.

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So those are other ways to
describe our kinematics.

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You talked about metres
per second, before.

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What's the word for that?

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Speed.

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Speed.

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And then, we also have velocity.

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So if we go even further, to how
fast your movement is changing,

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you have acceleration--

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how much your speed is changing.

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So right now, Victor is not
really accelerating up at all.

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But then, all of a sudden,
he accelerates up fast,

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stops, and comes back down.

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So those are our three main
things we talk about is that

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distance, the position, whether
it's in scalar and vector;

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that velocity, whether
it's in scalar or vector--

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as just a speed or
velocity with a direction--

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in a linear and angular way;
and then also acceleration,

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that change in rate of velocity.

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Those are our main
kinematic variables.

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In kinetics, that's a
little harder to look at.

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So right now, Victor actually
has a force applied to him.

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Do you remember what we
talked about in the beginning?

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What's my favourite force?

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Gravity.

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Gravity.

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So that gravity
is keeping Victor

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from floating out into space.

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So the gravity is
pushing up into Victor,

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and Victor is pushing back.

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If he pushes down more, he's
then pushing against gravity

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to build up some
energy in his body,

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and then release that kinetic
energy so he can move upwards.

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So what actually happens
internally, in his body,

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is he's using his
muscles to create

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kinetic energy to actually
move that power into generating

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a jump.

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Do you have a favourite force,
or do you also like gravity?

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It was gravity.

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Gravity is pretty good, too.

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I like staying on the ground.

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So forces also exist--

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a big thing when we talk about
kinetics is static and dynamic.

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So static is when
you stay still.

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So that's how we look at
how his body is moving.

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So if we're going to do a
static analysis of his body,

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the force applied would be from
gravity up, and then the weight

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from his body down--

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so that counterbalance
to keep him stationary.

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When we talk about
dynamic motion,

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it is how the forces then
go throughout your body

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to create movement.

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So, say, if I was
going to push Victor,

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I'm then putting
a force onto him

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that makes him go from
static to dynamic movement.

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You can quantify that force,
or you could just qualitatively

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say, Kayla, that's mean.

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The other aspect, with kinetics,
that we like to talk about

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is balance.

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You've done a bunch of
work with balance, right?

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Yeah.

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Yeah, so balance is just that
ability to stay at equilibrium.

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And so you could see, Victor is
just balancing on his two feet,

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here.

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When we look at balance from
a quantitative perspective,

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we actually look at
that centre of gravity.

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Do you know where your
centre of gravity is?

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Around here.

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Yeah, it's just a little
bit below your belly button.

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So right now, because we
look at-- all of his body has

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different weight, his centre
of gravity is right here.

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But if he was going
to stand on one foot,

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his centre of gravity would
shift because there's only one

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point of contact
with that force.

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And then if, say, you were
going to move to the side--

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yeah, can you stay like that?

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I can try.

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Yeah, how's your balance, there?

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So his centre of gravity
is shifting even more.

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And then when he can't
overcome, internally,

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that centre of gravity,
he loses his balance.

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I almost fell.

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All right.

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So that's just a
basic introduction

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to human biomechanics.

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There's a lot more
in our worksheets,

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and then there's
a lot more if you

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want to go look at any other
type of physics textbook

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or biomechanical resource.

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Remember, this is a little
bit more complicated

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than you might have
seen, but there

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are a general set of vocabulary
that's used to describe things.

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So as you're talking
about movement,

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there's different things
that you can analyse--

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that you might know existed--

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and then there's also
different ways to describe what

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you're analysing so that
everybody can understand.

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Again, it's important
to note-- you don't

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have to memorise this now.

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This is just an
introduction so that you

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know these things exist, and
then you can look for them.

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When you read something
and you find these terms,

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you know what they mean and
you can come back to this video

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and review these things.

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All right, see you later.

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[EXIT MUSIC]

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