Chapter 2: Kinematics and Kinetics Introduction

Summary

This 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

00:00

📚 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.

05:00

🏃‍♂️ 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.

10:01

⛷ 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.

Keywords

💡Kinematics

Kinematics is the study of motion without considering the forces that cause it. It is a fundamental concept in biomechanics and is central to the video's theme of understanding motion. In the script, kinematics is described as having three key measures: distance, speed, and acceleration. The example given is calculating average speed by dividing the distance traveled by the time taken, such as driving six miles in half an hour, resulting in a speed of 12 miles per hour.

💡Motion

Motion is the act of moving or being moved and is the core subject of the video. It is the basis for discussing kinematics and kinetics. The script explains that motion can be described by how far an object travels (distance), how quickly it moves (speed), and how its speed changes (acceleration), all of which are essential to understanding biomechanics.

💡Speed

Speed is a measure of how fast an object is moving, defined as the distance traveled per unit of time. In the script, speed is used to illustrate the concept of motion by calculating the average speed of a car traveling six miles in half an hour, which is 12 miles per hour. Speed is a key component of kinematics.

💡Acceleration

Acceleration is the rate at which an object's speed changes over time. It is a critical concept in kinematics, as it describes how quickly or slowly an object speeds up or slows down. The script uses the example of a car accelerating from zero to 60 miles per hour and then decelerating to zero when stopping at a sign, to demonstrate positive and negative acceleration.

💡Kinetics

Kinetics is the study of the forces that cause or result from motion. It is a complementary concept to kinematics and is essential for a complete understanding of biomechanics. The script explains that while kinematics can be observed directly, kinetics requires tools to measure the forces involved in motion.

💡Force

Force is a push or pull upon an object that results in a change in its motion. It is a central concept in kinetics and is related to the video's theme of understanding the causes of motion. The script mentions that force is a component of various physical formulas, such as those for calculating pressure, torque, work, impulse, and momentum.

💡Linear Motion

Linear motion refers to movement along a straight path. In the script, it is one of the three types of motion discussed, with the example of a skier moving down a hill, where all points on the skier's body move the same distance in the same amount of time.

💡Angular Motion

Angular motion is movement around an axis, involving rotation. The script explains that angular motion can be measured in terms of angular displacement, such as degrees, and is relevant to the golf swing, where the body rotates through a certain angle in a given time.

💡Displacement

Displacement is the change in position of an object. In the script, it is differentiated into linear and angular displacement, with examples including the straight-line distance traveled and the angle through which a body part rotates, respectively.

💡Velocity

Velocity is the speed of an object in a given direction. The script explains that velocity can be calculated by dividing the distance traveled by the time taken, and it can be expressed in units like meters per second or miles per hour. Angular velocity is a specific type of velocity that measures the rate of rotation in degrees per second.

💡Pressure

Pressure is defined as force per unit area and is a kinetic measure discussed in the script. It is an example of how force is involved in various physical phenomena and is calculated using force as part of its equation. The script mentions pressure as one of the kinetic measures that can be analyzed in biomechanics.

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