Twisting...What You Need To Know

[Stretchsportguy]

The forces in a rotating object project outward from the axis of rotation. The further away you get from the center, the greater the force becomes due to the increase in speed. The further away from the center, the more forces there are.

Any changes relating to the length of the object that is spinning results in changes of the forces.

Hence changing the length of the body by bending, dropping an arm, a forearm, a shoulder, bringing one leg in more than the other, tilting the head to the side with the arms already at your sides, etc., affects these forces in that they increase or decrease. The off balance of doing this on one side of the body while rotating is what creates the momentum for twisting because the body wants to speed up on that side.

http://iweb.tntech.edu/murdock/books/v2chap1.pdf

 

[gymcoach26]

Where is your source from stretch?
I clicked the link and there was no author, organization, institution etc? For all we know you wrote it yourself.

 

[Deleted member D3987]

here is where it is from and credit given....sorry so long. be certain to read the very bottom paragraph with its advice.

Worked Examples from Introductory Physics
(Algebra–Based)
Vol. I: Basic Mechanics
David Murdock, TTU
September 9, 2008
2
Contents
Preface i
1 Mathematical Concepts 1​

1.1 The Important Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

1.1.1 Measurement and Units in Physics . . . . . . . . . . . . . . . . . . . ​

​

1

1.1.2 The Metric System; Converting Units . . . . . . . . . . . . . . . . . . ​

​

2

1.1.3 Math: You Had This In High School. Oh, Yes You Did. . . . . . . . . ​

​

3

1.1.4 Math: Trigonometry . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

5

1.1.5 Vectors and Vector Addition . . . . . . . . . . . . . . . . . . . . . . . ​

​

5

1.1.6 Components of Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

6

1.2 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

8

1.2.1 Measurement and Units . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

8

1.2.2 Trigonometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

10

1.2.3 Vectors and Vector Addition . . . . . . . . . . . . . . . . . . . . . . . ​

​

14

2 Motion in One Dimension 19
2.1 The Important Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

19

2.1.1 Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

19

2.1.2 Speed and Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

19

2.1.3 Motion With Constant Velocity . . . . . . . . . . . . . . . . . . . . . ​

​

20

2.1.4 Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

20

2.1.5 Motion Where the Acceleration is Constant . . . . . . . . . . . . . . ​

​

21

2.1.6 Free-Fall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

22

2.2 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

23

2.2.1 Motion Where the Acceleration is Constant . . . . . . . . . . . . . . ​

​

23

2.2.2 Free-Fall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

24

3 Motion in Two Dimensions 33
3.1 The Important Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

33

3.1.1 Motion in Two Dimensions, Coordinates and Displacement . . . . . . ​

​

33

3
4 CONTENTS
3.1.2 Velocity and Acceleration . . . . . . . . . . . . . . . . . . . . . . . . ​

​

34

3.1.3 Motion When the Acceleration Is Constant . . . . . . . . . . . . . . . ​

​

35

3.1.4 Free Fall; Projectile Problems . . . . . . . . . . . . . . . . . . . . . . ​

​

36

3.1.5 Ground–To–Ground Projectile: A Long Example . . . . . . . . . . . ​

​

36

3.2 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

39

3.2.1 Velocity and Acceleration . . . . . . . . . . . . . . . . . . . . . . . . ​

​

39

3.2.2 Motion for Constant Acceleration . . . . . . . . . . . . . . . . . . . . ​

​

40

3.2.3 Free–Fall; Projectile Problems . . . . . . . . . . . . . . . . . . . . . . ​

​

41

4 Forces I 49
4.1 The Important Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

49

4.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

49

4.1.2 Newton’s 1st Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

50

4.1.3 Newton’s 2nd Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

50

4.1.4 Units and Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

51

4.1.5 Newton’s 3rd Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

51

4.1.6 The Force of Gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

52

4.1.7 Other Forces Which Appear In Our Problems . . . . . . . . . . . . . ​

​

54

4.1.8 The Free–Body Diagram: Draw the Damn Picture! . . . . . . . . . . ​

​

56

4.1.9 Simple Example: What Does the Scale Read? . . . . . . . . . . . . . ​

​

56

4.1.10 An Important Example: Mass Sliding On a Smooth Inclined Plane . ​

​

58

4.1.11 Another Important Example: The Attwood Machine . . . . . . . . . ​

​

61

4.2 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

63

4.2.1 Newton’s Second Law . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

63

4.2.2 The Force of Gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

65

4.2.3 Applying Newton’s Laws of Motion . . . . . . . . . . . . . . . . . . . ​

​

65

5 Forces II 69
5.1 The Important Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

69

5.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

69

5.1.2 Friction Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

69

5.1.3 An Important Example: Block Sliding Down Rough Inclined Plane . ​

​

70

5.1.4 Uniform Circular Motion . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

71

5.1.5 Circular Motion and Force . . . . . . . . . . . . . . . . . . . . . . . . ​

​

73

5.1.6 Orbital Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

73

5.2 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

75

5.2.1 Friction Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

75

5.2.2 Uniform Circular Motion . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

78

5.2.3 Circular Motion and Force . . . . . . . . . . . . . . . . . . . . . . . . ​

​

80

5.2.4 Orbital Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

83

CONTENTS ​

​

5

6 Energy 87
6.1 The Important Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

87

6.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

87

6.1.2 Kinetic Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

87

6.1.3 Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

88

6.1.4 The Work–Energy Theorem . . . . . . . . . . . . . . . . . . . . . . . ​

​

89

6.1.5 Potential Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

89

6.1.6 The Spring Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

90

6.1.7 The Principle of Energy Conservation . . . . . . . . . . . . . . . . . . ​

​

91

6.1.8 Solving Problems With Energy Conservation . . . . . . . . . . . . . . ​

​

92

6.1.9 Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

92

6.2 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

93

6.2.1 Kinetic Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

93

6.2.2 The Spring Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

93

6.2.3 Solving Problems With Energy Conservation . . . . . . . . . . . . . . ​

​

94

7 Momentum 99
7.1 The Important Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

99

7.1.1 Momentum; Systems of Particles . . . . . . . . . . . . . . . . . . . . ​

​

99

7.1.2 Relation to Force; Impulse . . . . . . . . . . . . . . . . . . . . . . . . ​

​

99

7.1.3 The Principle of Momentum Conservation . . . . . . . . . . . . . . . ​

​

100

7.1.4 Collisions; Problems Using the Conservation of Momentum . . . . . . ​

​

102

7.1.5 Systems of Particles; The Center of Mass . . . . . . . . . . . . . . . . ​

​

104

7.1.6 Finding the Center of Mass . . . . . . . . . . . . . . . . . . . . . . . ​

​

105

7.2 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

106

8 Rotational Kinematics 107
8.1 The Important Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

107

8.1.1 Rigid Bodies; Rotating Objects . . . . . . . . . . . . . . . . . . . . . ​

​

107

8.1.2 Angular Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

109

8.1.3 Angular Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

110

8.1.4 Angular Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

111

8.1.5 The Case of Constant Angular Acceleration . . . . . . . . . . . . . . ​

​

111

8.1.6 Relation Between Angular and Linear Quantities . . . . . . . . . . . ​

​

112

8.2 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

113

8.2.1 Angular Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

113

8.2.2 Angular Velocity and Acceleration . . . . . . . . . . . . . . . . . . . ​

​

113

8.2.3 Rotational Motion with Constant Angular Acceleration . . . . . . . . ​

​

114

8.2.4 Relation Between Angular and Linear Quantities . . . . . . . . . . . ​

​

114

6 CONTENTS
9 Rotational Dynamics 117
9.1 The Important Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

117

9.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

117

9.1.2 Rotational Kinetic Energy . . . . . . . . . . . . . . . . . . . . . . . . ​

​

117

9.1.3 More on the Moment of Inertia . . . . . . . . . . . . . . . . . . . . . ​

​

119

9.1.4 Torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

119

9.1.5 Another Way to Look at Torque . . . . . . . . . . . . . . . . . . . . . ​

​

124

9.1.6 Newton’s 2nd Law for Rotations . . . . . . . . . . . . . . . . . . . . . ​

​

124

9.1.7 Solving Problems with Forces, Torques and Rotating Objects . . . . . ​

​

125

9.1.8 An Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

126

9.1.9 Statics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

128

9.1.10 Rolling Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

129

9.1.11 Example: Round Object Rolls Down Slope Without Slipping . . . . . ​

​

130

9.1.12 Angular Momentum . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

133

9.2 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

135

9.2.1 The Moment of Inertia and Rotational Kinetic Energy . . . . . . . . ​

​

135

10 Oscillatory Motion 137
10.1 The Important Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

137

10.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

137

10.1.2 Harmonic Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

137

10.1.3 Displacement, Velocity and Acceleration . . . . . . . . . . . . . . . . ​

​

140

10.1.4 The Reference Circle . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

141

10.1.5 A Real Mass/Spring System . . . . . . . . . . . . . . . . . . . . . . . ​

​

144

10.1.6 Energy and the Harmonic Oscillator . . . . . . . . . . . . . . . . . . ​

​

145

10.1.7 Simple Pendulum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

146

10.1.8 Physical Pendulum . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

148

10.2 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

149

10.2.1 Harmonic Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

149

10.2.2 Mass–Spring System . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

149

10.2.3 Simple Pendulum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

150

11 Waves I 151
11.1 The Important Stuff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

151

11.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

151

11.1.2 Principle of Superposition . . . . . . . . . . . . . . . . . . . . . . . . ​

​

152

11.1.3 Harmonic Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

154

11.1.4 Waves on a String . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

157

11.1.5 Sound Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

157

11.1.6 Sound Intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

158

CONTENTS ​

​

7

11.1.7 The Doppler Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

160

11.2 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

161

11.2.1 Harmonic Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

161

11.2.2 Waves on a String . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

162

11.2.3 Sound Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ​

​

162

8 CONTENTS
Preface
This booklet can be downloaded free of charge from:
Physics Study Guides
The date on the cover page serves as an edition number. I’m continually tinkering with
these booklets.
This book is:
• ​

​

A summary of the material in the first semester of the non–calculus physics course as

I teach it at Tennessee Tech.
• ​

​

A set of example problems typical of those given in non–calculus physics courses solved

and explained as well as I know how.
It is not intended as a substitute for any textbook suggested by a professor. . . at least not
yet! It’s just here to help you with the physics course you’re taking. Read it alongside the
text they told you to buy. The subjects should be in the rough order that they’re covered
in class, though the chapter numbers won’t exactly match those in your textbook.
Feedback and errata will be appreciated. Send mail to me at:
murdock@tntech.edu
i​

i

​

 

[Stretchsportguy]

I'm going to make a lot of people happy. But before I do, tell me what it is about "tilt" that makes it work. Explain it in your own terms in language that is easy to understand.

Go ahead, make my day.

Remember that one great advantage of "tilt" is that it puts you in a position to borrow energy from the flip and transfers that energy into the twist. Expand on this. Also remember to explain how "tilt" allegedly creates "twist." I gotta see someone tell me that story...

 

[Stretchsportguy]

Speak so that even a 7th grader would understand. I'll give you an hour or more to answer. If you need more time then let me know.

 

[Stretchsportguy]

Oops...please include why you only need a little energy from the flip to get a lot of energy to twist. Sorry, you can have an extra 15 minutes.

 

[Geoffrey Taucer]

First of all, if you triple post again, I'm going to ban you. Please acquaint yourself with the "edit" function.

Second of all, if you continue to state your arguments in such a rude and unnecessarily aggressive manner (ie, arguing like a caveman), I'm going to ban you.

Ok, with that out of the way, let's look at this. Please stop me at any point here where you disagree.

Oops...please include why you only need a little energy from the flip to get a lot of energy to twist. Sorry, you can have an extra 15 minutes.

Ok, first off, we can agree that a body with a shorter turning radius requires less energy to turn, yes?

You only need a little energy from the flip to get a lot of twist because your radius about the vertical axis (ie axis of twisting) is MUCH MUCH shorter than your radius about the lateral axis (ie axis of flipping).

In terms a 7th grader could understand: are you a sumo wrestler? No? Then your height is greater than your width.

Therefore, it takes far more energy to rotate about an axis perpendicular to your height than one perpendicular to your width.

I'm going to make a lot of people happy. But before I do, tell me what it is about "tilt" that makes it work. Explain it in your own terms in language that is easy to understand.

Go ahead, make my day.

Remember that one great advantage of "tilt" is that it puts you in a position to borrow energy from the flip and transfers that energy into the twist. Expand on this. Also remember to explain how "tilt" allegedly creates "twist." I gotta see someone tell me that story...

Sadly, I don't believe I can explain this in simpler terms than I already have.

So we'll have to look at this from a different angle. We can agree that the article we have both been referencing, the one you accuse me of not understanding, is an accurate analysis of the mechanics of twisting, correct?

More to come when you have responded.

 

[gymdog]

I was really hoping you'd go over the allotted hour so we could see what happened. But alas.

 

[bogwoppit]

I was really hoping you'd go over the allotted hour so we could see what happened. But alas.

Personally I was hoping for spontaneous human combustion, 'cos I've had enough!

 

[bogwoppit]

Speak so that even a 7th grader would understand. I'll give you an hour or more to answer. If you need more time then let me know.

THis is is so rude I feel like calling in the manners police! You need to read the rules. Here are a few guidelines ALL internet users should apply.

• Avoid typing in all caps or all bold, as this is the equivalent to yelling on an internet forum.
• Avoid posting extremely long forum posts on a regular basis.
• Read all of the posts in the thread before posting on the internet forum. This will help forum participants avoid repeating points that have already been discussed in depth.
• Do not "hijack" forum threads. Stay on topic and avoid directing the thread away from the current line of conversation, particularly if the original poster is seeking an answer to a question. If you'd like to discuss a different issue or problem, it's best to start a new thread on the forum.
• Avoid derogatory remarks about fellow forum participants; if a forum participant has a problem that they'd like to address with another individual, it's best to discuss the issue off-forum rather than in a more public forum setting.
• When posting on a professional forum, like a forum for writers of a website, it's best to avoid derogatory remarks about the website, website staff, etc. Remember, there's a fine line between constructive and non-constructive criticism in many cases, and those lines can be blurred on the web due to the absence of indicators like tone of voice, facial expressions, etc.
• Remember your audience. Who's reading the web forum? It's important to keep this in mind when making forum posts, as some forum discussions may be inappropriate depending on the forum audience.
• Use emoticons and other symbols to indicate tone. When posting on an internet forum, there is an absence of indicators that help one to decipher tone and the forum poster's intention. In the absence of valuable voice tone, body language, facial expressions and other social cues, emoticons and symbols (smiley face, or "*smile*") can help make tone and intention clear to other forum participants.

​

 

[Geoffrey Taucer]

I was really hoping you'd go over the allotted hour so we could see what happened. But alas.

I considered it, but I think the result would simply be that he would continue to parade his ego about, and I think that's worn out it's entertainment value.

 

[Deleted member D3987]

I considered it, but I think the result would simply be that he would continue to parade his ego about, and I think that's worn out it's entertainment value.

uh oh...me thinks someone is back. heeeeeres johnny! [the shining...jack nicholson]

has chucky posted in a while?

 

[Stretchsportguy]

First time I'm reading the rules. Sorry about all the infractions. Not used to this. Been out of the circuit for over 30 years. I will not be able to post any renderings due to the limitations in the guidlines.

Your answer thus far Geoffrey was predictable and I thank you for stepping forward. You left out references to centrifugal forces. Any explanation of rotation without reference to centrifugal forces is incomplete. But I need room to expand on this. According to the rules I do not have enough leeway. I apologize for breaking the rules. I will not be able to post my renderings due to the rules without risk of being banned. Something I expected to happen. People resist the truth. I don't know why.

 

[Geoffrey Taucer]

First time I'm reading the rules. Sorry about all the infractions. Not used to this. Been out of the circuit for over 30 years. I will not be able to post any renderings due to the limitations in the guidlines.

Your answer thus far Geoffrey was predictable and I thank you for stepping forward. You left out references to centrifugal forces. Any explanation of rotation without reference to centrifugal forces is incomplete. But I need room to expand on this. According to the rules I do not have enough leeway. I apologize for breaking the rules. I will not be able to post my renderings due to the rules without risk of being banned. Something I expected to happen. People resist the truth. I don't know why.

You are perfectly welcome to explain calmly and respectfully why you disagree with me. I will not ban somebody for merely having a differing opinion. I will only ban you if you are rude and overly aggressive, or if you break any other forum rules.

 

[bogwoppit]

I had to break out the dictionary for "renderings". Not that I don't know what it means, more that I had never heard it applied to a forum post. Lo and behold the second use of it fits perfectly!

rendering [ˈrɛndərɪŋ]
n 1. the act or an instance of performing a play, piece of music, etc.
2. (Literary & Literary Critical Terms) a translation of a text from a foreign language
3. (Miscellaneous Technologies / Building) Also called rendering coat render a coat of plaster or cement mortar applied to a surface
4. (Fine Arts & Visual Arts / Architecture) a perspective drawing showing an architect's idea of a finished building, interior, etc.

Collins English Dictionary – Complete and Unabridged © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003

Stretch do you really mean that you cannot post your translations from foreign languages dues to the Chalkbucket rules?

 

[Geoffrey Taucer]

I was going to wait until stretch responded, but I'm about to sign off for the night, so I'll just have to continue assuming that he agrees the article that both he and I have referenced repeatedly in this thread is an accurate analysis of the mechanics of twisting.

A quick ctrl+f reveals that the word "drag" does not appear one single time in that entire article. Nor does the word "resistance." Nor does "centrifugal." (while centrifugal force does come into play any time we discuss rotation, all it means for twisting is that the gymnast's arms will be pulled out from the center, and she must work a little harder to keep the arms in while twisting than she would if she were stationary; centrifugal force has nothing to do with how the twist is initiated.)

However, it does, in the first paragraph under the section titled "creating tilt," say the following:

....When the same arm movements are made during a somersault this tilt results in twist as shown in the lower sequence.

Lowering the right arm and raising the left arm will cause the body to tilt to the left. This tilt will cause the body to twist to the left during a forward somersault. Similarly lowering the left arm will cause the gymnast to twist to the right during a forward somersault.

In other words, the very article you are referencing -- and accusing me of not understanding -- backs me up on this. And, in fact, the entire article is about using tilt to generate twist.

As for borrowing momentum from the flip and using it to twist, let's look at an article in the Feb, 2010 issue of Technique magazine, written by Peter Pidcoe, PT, DPT, PHD; Tony Gehman, and Donald Mcpherson:

...It is important to note
that the angular momentum is constant
once the gymnast is in free-flight. All the
gymnast can do is manipulate their body
shape to change angular velocity and
transfer energy between the flipping to
the twisting axes.

In simpler terms: the momentum has to come from somewhere; it doesn't just magically appear. So angular momentum must be "borrowed" from the flip and used to twist instead.

I seem to recall there being an excellent section on this in Gerald George's Championship Gymnastics: Biomechanical Techniques for Shaping Winners; unfortunately, I have lent my copy to another coach and cannot quote it from memory, but I will be happy to add Dr. George's thoughts on the matter when I get it back. If anybody else has a copy handy and feels like quoting relevant sections, feel free.

I don't seem to recall him using the term "drag" either.

 

[Stretchsportguy]

...With the risk of throwing caution to the wind, I'm going to cut this into small pieces in the hopes that I will not be banned. I've already stated a few things that for some reason even though they are true, have been resisted. The governing force in a rotating body is centrifugal force. The faster the object rotates and the longer the object is, the greater the force that is generated on the axis.

The tilt analysis is incomplete. Therefore it is impossible to discern a strategy that is useful from it. In other words I don't hear coaches advising gymnasts to work on their tilt. In and of itself tilt is not useful unless you understand what tilt does that makes it useful. And to figure that out, you need to relate it to the axis and centrifugal forces. The forces in a rotating body relate to and affect the axis. And the forces which are generated are centrifugal.

I am purposely repeating principles in the hopes that you will learn what is paramount and what is secondary.

The tilt analysis is incomplete again when the analyst fails to explain that if the arms are returned to the original position then the body also returns to the original position. Try it for yourself and see. There is an equal and opposite reaction at the other end of the body in the air.

Should the air borne diver or gymnast return the arms back to the position they started in, then the body returns to the original starting position. Straight. It does not matter that in between the beginning and the end, the diver was flipping.


If the tilt is sustained into a flip, the flipping body wobbles if it is bent. But as I explained in a previous post, wobbles are actually figure 8's due to rotation. The hips do a figure 8 from one side to the other as the twisting body flips over. If the body is not bent, then the diver remains twisting extended at an angle until the rotation is complete or arms are extended back where they were. (Note: cat twisting does not work in efficiently in flips eventhough it can turn you. Cat twisting is a turn that does not affect the centrifugal force vectors. This is a type of twist that uses internal body dynamics where the body is compressed or extended (piked) (hips lifted) (arched) then opened or compressed to turn out or in. Two of these in a row will result in a full turn. It is often described as hoola hooping in mid air. Related to the swivel hips skill on trampoline.)

The question still remains un-answered. What is useful about the tilt from a coaching aspect?

One thing the tilt does is corkscrew the rotation. The corkscrew is a skill being developed and perfected in some gymnastics schools but as yet has not been utilized significantly in the sport. This will soon change. The door is open to anyone who performs this skill first on the balance beam. Full twisting butterflies are also game.

I am borrowing the name applied to the corkscrew skill to describe what is occurring in a tilt that is useful. The tilt is useful because the body is leaned into the axis. Leaning into the axis as the body begins to rotate reduces the original stature that was rotating on that axis. Draw a horizontal line across the top of the head and where the feet were and you will see that the original top to axis and bottom to axis distances have been shortened. By reducing the stature that used to exist on the axis, your rotation speeds up. Unless of course you "borrow" that force to start twisting at an angle. The corkscrew and full twisting butterfly skills exaggerate this principle.
Twisting is always initiated by a change in centrifugal force vectors. The tilt itself only works to place the body in an asymmetrical position where the centrifugal vectors will be redirected when the body rotates.

The knowledge that a tilt leans you into the axis of rotation and shortens the stature that was in that axis is useful knowledge. Now you know where that flipping energy is coming from that is being borrowed to spin with. Tilt is always present when one arm is brought in before the other in mid air. It appears as a hip lift on one side and a shoulder drop on the other. This also explains how flipping energy is transferred to the twist from the flip.
Tilt then serves to transfer flipping energy to the twist. But tilt does not twist you. Changing the momentum vectors or centrifugal force vectors does that. Twist initiation has already been explained as one side of the body speeding up due to a reduced stature or shortened distances from the axis on that side.

All I can say is watch a lot of videos including ones in slow motion and you will see all of this is consistent and evident.

By now some people are already very happy. Its what happens when you finally understand something that means a lot to you and that never had a straight answer.

Drag is another term I borrowed for my own personal use. The fact that one arm remains long and keeps that side of the body long in relation to the axis, means that it will resist flipping more than the other side of the body where you have pulled in the arm. The long side of the body acts as a pivot bar or brake or I am calling it "drag." Therefore the side that you shortened the radius wants to speed up but guess what? The long side resists. The force vectors make a turn and start going into the other axis. Hence, you spin.

Please read the first paragraph again at this point. Thanks a bunch.

 

[Stretchsportguy]

Sorry for this subsequent post. The edit button disappeared. I can't get it to pull up. I've reloaded the page several times and even signed in on new tabs but no edit button.

Future renderings I intend to offer include how to take advantage of the figure 8 phenomenon that occurs during twisting flips as a result of tilt.

How to know where you are or where the floor is at all times during flipping and twisting.

How to twist fast.

How to stay level on full twisting or more vertical jumps and keep your feet under you for a square landing. Tilt interferes with straight jumps. What to do about it.

 

[Geoffrey Taucer]

...With the risk of throwing caution to the wind, I'm going to cut this into small pieces in the hopes that I will not be banned. I've already stated a few things that for some reason even though they are true, have been resisted. The governing force in a rotating body is centrifugal force. The faster the object rotates and the longer the object is, the greater the force that is generated on the axis.

The tilt analysis is incomplete. Therefore it is impossible to discern a strategy that is useful from it. In other words I don't hear coaches advising gymnasts to work on their tilt. In and of itself tilt is not useful unless you understand what tilt does that makes it useful. And to figure that out, you need to relate it to the axis and centrifugal forces. The forces in a rotating body relate to and affect the axis. And the forces which are generated are centrifugal.

Yes, that's what centrifugal force means. However, centrifugal force is merely something that happens once rotation has been initiated. It has nothing to do with actually initiating the rotation.

I am purposely repeating principles in the hopes that you will learn what is paramount and what is secondary.

The tilt analysis is incomplete again when the analyst fails to explain that if the arms are returned to the original position then the body also returns to the original position. Try it for yourself and see. There is an equal and opposite reaction at the other end of the body in the air.

Should the air borne diver or gymnast return the arms back to the position they started in, then the body returns to the original starting position. Straight. It does not matter that in between the beginning and the end, the diver was flipping.

Yes, I am well aware of this. This is what I meant when I said that the twist can be stopped in preparation for landing.

If the tilt is sustained into a flip, the flipping body wobbles if it is bent. But as I explained in a previous post, wobbles are actually figure 8's due to rotation. The hips do a figure 8 from one side to the other as the twisting body flips over. If the body is not bent, then the diver remains twisting extended at an angle until the rotation is complete or arms are extended back where they were. (Note: cat twisting does not work in efficiently in flips eventhough it can turn you. Cat twisting is a turn that does not affect the centrifugal force vectors. This is a type of twist that uses internal body dynamics where the body is compressed or extended (piked) (hips lifted) (arched) then opened or compressed to turn out or in. Two of these in a row will result in a full turn. It is often described as hoola hooping in mid air. Related to the swivel hips skill on trampoline.)

No disagreements here

The question still remains un-answered. What is useful about the tilt from a coaching aspect?

It is useful in that, as stated in the article that we're referencing, it creates twist. It transfers angular momentum from the lateral axis to the vertical axis (and to clarify, when I say "vertical," I mean vertical relative to the gymnast; the twist axis is not fixed, but rather rotates with the gymnast).

By the use of asymetrical arm movement (ie one arm going up while the other goes down, OR one arm going up/down more than the other) tilt is introduced, which causes twist.

Why does this asymetrical movement cause tilt? Simple; for every action, there is an equal but opposite reaction. If one arm goes down more than the other, you are in a sense rotating the arms to one side. Since this rotation was not initiated from the floor, the body must slightly counterrotate, due to the simple fact that angular momentum is conserved unless the body is acted apon by an outside force.

Asking why tilt is useful to coaching is like asking why height is useful to coaching. I wouldn't tell a gymnast "work on your height;" rather, I would tell the gymnast what specifically they need to do to get more height in whatever skill they're performing. Likewise, I wouldn't tell a gymnast to "work on her tilt;" I would, however, tell her specifically what she needs to do to achieve such tilt in order to cause her to twist.

One thing the tilt does is corkscrew the rotation. The corkscrew is a skill being developed and perfected in some gymnastics schools but as yet has not been utilized significantly in the sport. This will soon change. The door is open to anyone who performs this skill first on the balance beam. Full twisting butterflies are also game.

I am borrowing the name applied to the corkscrew skill to describe what is occurring in a tilt that is useful. The tilt is useful because the body is leaned into the axis. Leaning into the axis as the body begins to rotate reduces the original stature that was rotating on that axis. Draw a horizontal line across the top of the head and where the feet were and you will see that the original top to axis and bottom to axis distances have been shortened. By reducing the stature that used to exist on the axis, your rotation speeds up. Unless of course you "borrow" that force to start twisting at an angle. The corkscrew and full twisting butterfly skills exaggerate this principle.
Twisting is always initiated by a change in centrifugal force vectors. The tilt itself only works to place the body in an asymmetrical position where the centrifugal vectors will be redirected when the body rotates.

When we're discussing twisting saltos, we're talking about a small amount of tilt. When we're discussing a corkscrew or a twisting butterflies, we're talking about approximately 90 degrees of tilt.

By now some people are already very happy. Its what happens when you finally understand something that means a lot to you and that never had a straight answer.

Why thank you. Clearly nobody here has ever asked about twisting and gotten an answer before. I don't know what we'd do without you.

Drag is another term I borrowed for my own personal use. The fact that one arm remains long and keeps that side of the body long in relation to the axis, means that it will resist flipping more than the other side of the body where you have pulled in the arm. The long side of the body acts as a pivot bar or brake or I am calling it "drag." Therefore the side that you shortened the radius wants to speed up but guess what? The long side resists. The force vectors make a turn and start going into the other axis. Hence, you spin.

Except "drag" has a completely different meaning in physics. Physics HAS a term for what you're describing: it's called "moment of inertia." Why not simply use the term that already exists rather than grabbing some random other term?

Sorry for this subsequent post. The edit button disappeared. I can't get it to pull up. I've reloaded the page several times and even signed in on new tabs but no edit button.

Odd. I'll ask JBS about it.

 

[bogwoppit]

AGH!!!!

The edit button disappeared because!!!!! Because maybe there is a god and maybe he knows this thread has gone on way tooo long.

We have had great threads on twisting before, they have involved discussion and not pontification. This thread has no value as nothing new is being added, just a whole ton of confusion.

Plus whenever I hear the word drag I think of Priscilla Queen of the Desert"! Now that is DRAG!!

Enough with the "renderings", I gave you the English definition of this word. It is not the correct word for your typing.