Chapter 7 - Angular Kinetics in Sports

Study of rotation and the forces that cause and act on rotation

Angular Kinetics

Angular kinetics is all about what 2 things?

Rotation and forces acting on rotation

What do rotating objects turn about?

An axis of rotation

What is another term for rotation around an axis

Angular Motion

What can gravity do in movement?

Initiate OR limit rotation

What happens when an athlete falls from a higher height?

Greater final velocity

Does a falling object accelerate forever? Why not? What does it eventually reach?

No; Air resistance increases; Terminal Velocity (~200 km/h)

Balance point where weight is evenly distributed.

Center of Gravity

What's another way to describe COG?

Balance Point

Why is COG different for each person?

Body is made of different materials with different weights/densities

Where is COG typically in males?

Around belly button (57% of height)

In females, COG is ________ _____ than in males.

slightly lower

What affects where your COG is located?

Body build (muscle distribution)

Can athletes change their COG? How do they change it?

Yes; By moving their limbs (MOST important factor)

What happens to COG when stepping forward?

It shifts forward

What determines how much COG shifts?

How much mass moves and how far it goes

Why do wrestlers/judo athletes lower COG?

To increase stability

Why do sprinters shift COG foward?

Faster start

Why do throwers adjust COG?

Apply maximum force over time

When is an athlete's flight path determined?

At takeoff

What shape is the flight path? Why is it curved?

Parabolic (curved); Gravity pulls downward

What is angular momentum (H)?

Amount of motion in a rotating object

Formula for angular momentum?

H = I x ω

What is moment of inertia (I)?

Resistance to rotation (depends on mass + distribution)

Wheat is angular velocity (ω)?

Speed of Rotation

What 3 things affect angular momentum?

Mass, Distribution of Mass, Speed of Rotation

What is radius of gyration?

Distance mass is from the axis

What matters most for moment of inertia?

Distance from the axis

How do you increase angular momentum? Why can't you maximize all 3 easily?

Increase mass, Move mass farther from axis, Increase speed (ω); You must balance them

Batting example: how to increase H?

Heavier bat, extend arms, swing faster

Why do high jumpers swing arms and leg upward? What does this movement do?

Generate more angular momentum; Adds to force from the ground

Which law is Conservation to Angular Momentum related to?

Newton's 1st Law

What happens to spinning objects during conservation of angular momentum?

Keeps spinning unless stopped

When is angular momentum constant?

In flight

During conservation of angular momentum, if one factors factor decreases, what must happen?

Another must increase

If moment of inertia increases, what happens to angular velocity?

It decreases

If moment of inertia decreases, what happens to angular velocity?

It increases

What determines a diver's angular momentum?

Takeoff, Mass, Body position

Why can't divers create new momentum in air?

No surface to push against

1. When a figure skater's arms are OUT, what happens? 2. When they are IN, what happens? 3. Why? 4. What stays constant?

1. Large inertia, slow rotation

2. Smaller inertia, faster rotation

3. Mass moves closer to axis

4. Angular momentum

If legs move upward in the air, what happens to upper body? Why

Moves downward; Equal and opposite reaction

What determines moment of inertia?

Mass + distance from axis

What matters more in moment of inertia? Mass or Distance from Axis?

Distance from Axis

Why does bending knees reduce inertia?

Mass moves closer to axis

Why do jumpers rotate arms'legs foward? What happens without rotation?

Get better landing position; Feet hit sooner, which leads to a shorter jump

Which law explains Transferring Angular Momentum

Newton's 3rd Law

How is angular momentum transferred?

Between body parts

What matters most in transferring angular momentum?

Mass + angular velocity

Do cats need angular momentum to twist?

No

How do cats land on their feet? What do they reduce?

Rotate body segments against each other; Rotary inertia of one part

What determines angular momentum overall?

Mass = distribution + angular velocity

Does angular momentum change in flight? What changes instead?

No, it stays constant; Speed changes based on body position

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