Chapter 2: Kinematics and Kinetics Introduction
Summary
TLDRThis script delves into the fundamental concepts of biomechanics, focusing on kinematics—the study of motion—and kinetics, which involves the forces behind motion. It explains the three key measures of motion: distance, speed, and acceleration, and contrasts them with angular displacement and velocities. The discussion highlights the importance of understanding both the description of motion and the forces causing it, particularly in the context of sports performance. The script also touches on the complexities of measuring these biomechanical aspects and their applications in improving athletic performance.
Takeaways
- 📚 Kinematics is the study of motion's description, focusing on distance, speed, and acceleration.
- 📏 Distance is a fundamental measure in kinematics, indicating how far an object has moved.
- ⏱ Time is crucial for calculating average speed, which is the ratio of distance to time taken.
- 🔢 Speed is quantified as the rate of motion, typically measured in miles per hour or meters per second.
- ⏩ Acceleration is the rate of change of speed, which can be positive (speeding up) or negative (slowing down).
- 🔄 Kinetics involves the study of forces that cause or result from motion, differentiating it from kinematics.
- 🤸♂️ Both linear and angular movements are types of kinematics, with the latter measured in degrees for sports like golf.
- 📊 Angular velocity, such as Rory McIlroy's pelvic angular velocity, is significant in sports performance analysis.
- 🔄 General motion in biomechanics refers to a combination of translations and rotations happening simultaneously.
- 🏌️♂️ The golf swing is an example of general motion, involving both translation and rotation.
- 🔧 Kinetic measures like force and pressure are essential for understanding the cause of motion, complementing kinematic data.
Q & A
What is kinematics in biomechanics?
-Kinematics is the study of the description of motion, which includes measures such as distance traveled, speed, and acceleration.
How is speed calculated in kinematics?
-Speed is calculated by dividing the distance traveled by the time taken to travel that distance.
What is acceleration in the context of motion?
-Acceleration is the rate at which an object speeds up or slows down, and it can be positive (speeding up) or negative (slowing down).
What is the difference between kinematics and kinetics?
-Kinematics deals with the description of motion, while kinetics is concerned with the forces causing or resulting from motion.
What are the three basic measures of kinematics?
-The three basic measures of kinematics are distance (how far), speed or velocity (how fast), and acceleration or deceleration (how quickly the speed changes).
Can you explain the concept of angular displacement in kinematics?
-Angular displacement refers to the measurement of the angle through which a body rotates, typically measured in degrees.
What is the significance of Rory McIlroy's pelvic angular velocity in golf?
-Rory McIlroy's high pelvic angular velocity, which is the rate at which his pelvis rotates, is believed to contribute to his exceptional driving distance in golf.
What are the two types of motion described in the script?
-The two types of motion described are linear translation, where all points on a body move the same distance in the same time, and rotation, where points move through the same angle but different distances.
What is the term used to describe a motion that is a combination of translations and rotations?
-The term used to describe a motion that is a combination of translations and rotations is general motion.
How is pressure related to force in kinetics?
-Pressure is a kinetic measure that involves force as part of its calculation, along with other factors such as area.
What is the difference between linear and angular velocities in terms of units?
-Linear velocity is measured in units like meters per second or miles per hour, while angular velocity is typically measured in degrees per second.
Outlines
📚 Introduction to Kinematics and Kinetics
The paragraph introduces the basic definitions of biomechanical terms, focusing on kinematics, the study of the description of motion, and kinetics, the study of the forces causing or resulting from motion. It explains how motion is described through distance, speed, and acceleration, using everyday examples like driving a car. It also differentiates between kinematic measurements (distance, speed, acceleration) and kinetic measurements (forces), highlighting the importance of understanding both in biomechanics.
🏃♂️ Measuring Motion and Forces in Biomechanics
This section delves deeper into kinematic and kinetic measurements, explaining how we observe and measure motion through video cameras and 3D motion capture systems. It discusses the importance of new technologies in measuring forces that cause motion, such as those provided by Swing Catalyst products. The paragraph reiterates the three primary kinematic measures—distance, speed, and acceleration—and introduces the concept of angular displacement, using examples like Rory McIlroy's pelvic angular velocity to illustrate these concepts.
⛷ Understanding Linear and Angular Motion
This paragraph explains the different types of motion—linear and angular—and their relevance in activities like skiing and golfing. It describes linear translation as motion through the same distance in the same amount of time and angular motion as rotation around a point. The example of speed skaters switching lanes to equalize distance highlights these concepts. The paragraph also introduces general motion, a combination of linear and angular motions, and discusses the kinematic sequence in the golf swing, emphasizing the importance of understanding both types of motion in biomechanics.
🎯 Kinematic and Kinetic Measures in Golf
The final paragraph focuses on applying kinematic and kinetic measures in golf, discussing how these measurements are taken in linear and angular terms. It explains how velocities and accelerations are calculated, and introduces the kinematic sequence, which is crucial for transferring energy efficiently in a golf swing. The paragraph uses Rory McIlroy's swing as an example to discuss how golfers decelerate their pelvis to transfer energy to their thorax and arms, and speculates on the long-term impact of such motions on an athlete's body.
Mindmap
Keywords
💡Kinematics
💡Motion
💡Speed
💡Acceleration
💡Kinetics
💡Force
💡Linear Motion
💡Angular Motion
💡Displacement
💡Velocity
💡Pressure
Highlights
Kinematics is defined as the study of the description of motion.
To describe motion, three essential measures are distance, speed, and acceleration.
Speed is calculated as the average distance traveled over time, measured in miles per hour.
Acceleration is the rate at which an object speeds up or slows down.
Kinematic measures include displacement, velocity, and acceleration.
Kinetics involves the study of forces causing or resulting from motion.
Modern products like Swing Catalyst enable the measurement of kinetic forces in motion.
Kinematics can be observed with a video camera or a 3D motion capture system.
Kinetics requires specialized tools to measure the forces involved in motion.
Linear motion refers to movement in a straight line, such as a skier going down a hill.
Angular motion is movement around an axis, such as a golfer's rotation during a swing.
Golf swing involves a combination of linear translation and angular rotation.
The sequence of motion in golf, such as the order of translation and rotation, is a topic of biomechanical study.
Kinematic sequence is important for energy transfer in sports like golf.
Rory McIlroy's high pelvic angular velocity is an example of advanced kinematic measurement.
Biomechanical analysis can help improve athletic performance by understanding motion and force.
Understanding the difference between linear and angular kinematics is crucial for analyzing sports movements.
The practical application of biomechanics in sports can lead to better training and performance.
Advanced motion capture systems provide detailed data on angular velocities and accelerations.
Biomechanical studies can reveal the secrets behind exceptional athletic performance.
Transcripts
so some basic definitions biomechanical
terms that we need to realize so the
first term we're going to talk about is
kinematics and when I teach this to my
undergraduate students in Los Angeles I
always tell them kinematics has an
eminent and M stands for motion and so
kinematics is the study of the
description of motion and so if I had to
describe motion there's three things I
need to know if I was going to describe
any motion to you the first thing I need
to know is how far you went how many
people drove here today how far did you
come six miles okay so that is a measure
of the distance he went how long did it
take you 25 minutes let's say it took
you half an hour because it's going to
make my math way easier okay good okay
so if he went six miles and it took him
half an hour he went on average how fast
anybody do that math twelve my head
twelve miles per hour right so you went
12 miles per hour and was 12 miles per
hour a measure of miles per hour would
be a measure of speed exactly right so
we can know how far you went you need to
know how long it took to calculate the
average speed or how long or how quickly
or how fast you went and then we also
need to know a third thing
the third measure that describes motion
is something called accelerations which
is basically how quickly or slowly you
speed up or slow down and so obviously
he didn't drive you didn't get in your
car and go 12 the whole time right no
you probably sped up to 50 or so if
you're on a freeway no okay 60 good and
then down to zero while you wait good
and so if he's sitting his car and he's
going zero miles per hour and a couple
seconds later he's going 60 miles per
hour
he just accelerated so he went from zero
to 60 in a certain amount of time that's
a positive or an acceleration and he's
going 60 and he pulls up to a stop sign
what does he got to hit the brake good
oh well done yeah or the sign or a brick
wall sure and so when he hits the brake
that's going to be he's going to be
going from 60 back down to zero and
that's a negative acceleration or
deceleration so there's three types of
kinematic measures we can measure how
far how fast and then how quickly so
it's a displacement or distance you went
speed or velocity and then acceleration
or deceleration all of those things are
simply describing motion well then our
other term is kinetics and in the study
of K'NEX is a study of the forces
causing or resulting from motion and so
remember things don't move without
forces so if we measure only kinematics
and anything that we use video camera
wise to measure movement is going to
measure kinematics and so we've been
measuring kinematics for years even if
you're not measuring it you've been
watching it with your phones or your
video cameras but we haven't been able
to measure the kinetics or the forces
that cause that motion for very long and
so now we have some products that allow
us to do that which I think can help us
make our players get better much more
quickly so kinematics is motion the
description of motion we can see that
with a video camera with a phone with a
3d motion capture system some of the
fancy 3d motion capture systems we have
now kinetics forces the cause motion we
can't really see those we need something
to help us measure that and swing
catalysts now has some products that we
can do that so some of the measures of
kinematics like we said are there's only
basically three of them there's how far
you went the distance you went there's
how fast you went the speed or velocity
that you had and then how quickly you
sped up or slowed down which is
accelerations or decelerations and we
got to remember that these things can
happen in a straight-ahead sense so you
told me that you went six miles which is
a linear distance but if I'm standing
here and I twist my shoulders this far
how far did they go
I'm here to here you had to measure that
if I went from here 90 degrees sure and
that's a measure of angular displacement
right so I can move 90 degrees that's a
distance that I went in an angular way a
lot of people now are talking about Rory
McIlroy's pelvic angular velocity have
you heard about this he's probably had
the highest pelvic angular velocity that
anyone's ever measured so he gets his
pelvis moving very quickly I think it's
something like 1,200 degrees per second
that's probably why he hits it so far
and so we can talk about linear sense so
a linear distance would be in miles
kilometers inches feet anything that
measures a straight-ahead distance most
time when we measure angular distance
we're going to measure it in degrees so
we're going to measure 90 degrees or 180
degrees or whatever and then when we
measure velocities we just have to
divide our linear distance by time so we
can have meters per second we can have
miles per hour we never kilometers per
hour and then an angular sense we can
have degrees per second degrees per hour
most time angular is going to be in
degrees per second and then the
accelerations are a little bit more
complex we'll get to those in a second
kinetic measures
so remember kinetics has anything to do
with force so one thing you can measure
kinematics is motion kinetics is force
and so in level 2 we're probably get
into a little bit more of the formulas
the physical formulas that calculate
things like torque and work and impulse
and momentum and power if you look at
some of the formulas or if you look at
the formulas that calculate those things
force as part of that equation the only
one we're going to talk about today is
pressure so force is part of the
equation to calculate pressure so
anything that has to do with force is
going to be a kinetic measure the only
two we're going to talk about today are
just plain old force and then pressure
as well and those are the kinetic
measure and again you can see kinematics
you can't see kinetics you need
something to help you see kinetics and
so anytime we move we can move in one of
three ways if you look at this skier
going down a hill if you look at any
point on that skiers body it's going to
move through the same distance in the
same amount of time so if you look at
their ear their hip their wrist
their knee their ankle all of those
things are going to move the same
distance in the same amount of time we
call that a linear translation so that
thing's moving linearly its translating
as it moves down the hill so there's one
type of motion we can do is linear
motion and that happens in the golf
swing so if I go back to the top of the
backswing my trunk is going to translate
on top of my front foot a lot of that
time
okay so if this moves from here to here
in a linear sense that's a linear
translation type motion but that doesn't
happen in isolation while that's
happening we're also rotating so we can
move in a linear sense which we call
translations or we can move in an
angular sense which we call rotations
and so if we do a hamstring curl on a
hamstring machine in the gym and we look
at any point along my lower leg or my
foot it's going to move through the same
angle in the same amount of time but
it's not going to move through the same
distance so if you think about it if I
have a point right here on my calf and I
take another point down here in my foot
and I do this which point moved through
a greater distance the point on my foot
right so I was in Norway last weekend
and I was watching speed skating on the
TV and speed skaters they race against
each other and they go out and they do
one loop and then they cross over right
so the guy in the outside lane goes to
the inside lane because if I stayed in
the outside lane the whole time I'd have
to go a further distance and the guy on
the inside line so they cross over so
that they skate the same distance so the
further you get away from the point
that's the axis of rotation the further
that thing is going to move in a linear
sense so all those points don't go
through the same linear distance in the
same amount of time but they go through
the same angle so if I move purely
angular that's a pure rotational type
movement and that happens in the golf
swing so if my pelvis starts here and it
rotates through there that's a rotation
or an angular motion but in golf both of
those things happen at the same time and
so in in biomechanics what we call that
type of motion is just general motion
which is a combination of translations
and rotations so if you think of the
downswing from here I'm going to
translate and rotate all those things
are going to happen simultaneously and
some people now are talking about the
sequence of motion in terms of when
those things happen should we translate
first and then rotate should we rotate
and then translate do we want to do them
at the same time we don't really know
the answer that question but a lot of
people are talking about the linear and
angular kinematic sequence if you've
heard those terms before we're learning
a lot more about that but what you need
to know right now is the golf swing is a
general motion its translations and
rotations happening at the same time so
if we talk about our kinematics in
linear terms our kinematics can be
measured in
anything that measure the distance so
feet inches miles kilometers do you guys
do miles here for like road signs really
that's weird
actually like a metric system country as
well okay I don't to cause any
international incidents here so let's
leave it that so miles inches feet
kilometers anything that measures a
straight-ahead distance if we divide any
of those things by a unit of time that's
going to be a velocity or a speed so if
we take a kilometer and we divide it by
an hour kilometers per hour that's going
to be a velocity or a speed and then if
we do an acceleration we're not going to
talk too much about accelerations but if
the time term is squared on the bottom
that's going to be an acceleration so
meters per second squared miles per hour
squared don't worry too much about that
that might be in level three or level
four but decided where we're going to
put that yet it's a little more complex
and then in angular terms if you move an
angular terms pretty much the only one
that we care about is golf pros is
degrees not too often you're going to
talk in revolutions or radians if you're
a figure skating coach you'll talk in
revolutions right I did a three and a
half revolution whatever they call those
jumps salchow or whatever yeah whatever
they're called so we're going we don't
talk in revolutions in golf we talk in
degrees so that's probably the only one
we care about in terms of angular
displacement and then if we divide it by
seconds degrees per second a lot of the
3d motion capture systems will give you
torso pelvic angular velocities and
degrees per second or that's pretty much
the only thing they give you and then a
lot of the motion capture systems now
will give you the rate of acceleration
and deceleration of the different
segments so we can see the rate of
deceleration on the downswing of your
pelvis because it's really important
that once you get your pelvis moving
fast you have to slow it down to
transfer that energy up to your thorax
and then transfer it to the arm and then
transfer it to the club that's what we
call the kinematic sequence and one of
the things that they think Rory does
really well is slow down his pelvis so
he gets it moving faster than anyone's
ever measured and then at the end it
turns around and comes backwards so he
slams on the brakes and some people are
arguing about how he does that whether
it's with muscle activity or whether
he's just ramming his hip bones into
each other and
the answer to that question will
probably come twenty years down the road
if he falls apart and it might be he's
ramming his hip bones into each other
who knows we don't really know the
answer to that question yet but so if
we're moving in an angular sense it's
going to be in degrees if it's a
velocity it's going to be degrees per
second and some of the you'll see some
of the 3d motion capture systems will
give you accelerations angular
accelerations or decelerations so if
it's a positive number it's an
acceleration with a negative number and
it all be in degrees per second squared
generally
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