Center of Gravity and Stability (Biomechanics)

Write the formula for angular momentum.

(L) = mr x ω moment of Inertia x angular velocity

Where should the line of gravity be if the person wants to remain in the same position and be stable if he or she is pushed from behind?

(Low to the ground, so ground reaction force is really low.) Stay inside base so you can make quick movements if needed.

Describe how to determine the base of support.

Analyze the area you have around you and your feet, then determine how much space you have to move along the line of gravity all while staying within the space or "circle" you have.

List the 3 variables in angular momentum.

Angular momentum=moment of Inertia x angular velocity (L = I x ω) I = mass x radius (similar to R x RA = Torque)

Which picture on slide 9 provides the best stability?

Both your hands and feet on the ground

T or F All balance tests will have a strong correlation among each other if the same group is measured on all of the tests.

False

T or F Females always have better balance than males.

False

T or F The center of gravity is a fixed position in the body.

False

Where is the COG relative to the support foot to accelerate?

Front of it

Where is the COG relative to the support foot to decelerate?

Front of it

What effect does the height have on balance and stability?

Height of center of gravity changes with body position

What is the best position of the COG to decelerate?

High

A low COG during throwing or hitting produces primarily what type of ground reaction force?

Horizontal

Slide 11, if the girl leaned left or right, when would she start falling?

If she's standing up, she can lean over about 30 degrees, but if her hands are up she can only move about 20 degrees before falling

What effect does increased mass have on the stability of a stationary object?

It effects because it could make someone change their base and topple over (Ex. Johnny Bravo)

Slide 11, who has the best stability?

It honestly depends on the direction they are moving, either front to back or left to right

How long is angular momentum maintained if there is no outside force to oppose it?

It'll keep going until it is acted on (inertia). It has the same momentum unless an outside force stops it (wind, ground, etc.)

List the 2 variables in linear velocity.

Linear Momentum= mass x velocity Low center of gravity Most of forces pushing against the ground horizontal, and you want the center of mass towards the front. Push and transfer to front side.

What is the best position of the COG to accelerate?

Low

Which is best position for the COG to change directions?

Low

Based on the pic of Lincecum #55, do you want a low or high COG?

Low COG

Who has a higher center of gravity, males or females?

Males

Slide 14, how does the skater increase the spin rate?

Push against the ground and crates angular momentum of her body to spin. The momentum she has created stays the same because theirs very little friction in ice and skates. If she wants to speed up she'll out her arms together towards the center of her body and tucks into a tiny ball and then spreads her arms when she wants to sow down. Overall her angular momentum stays the same.

How is angular momentum created in the body during a throw?

Pushing angular momentum and transfer up the chain into the body and up the arm. Push against the ground which causes angular momentum. (use your whole body) How much mass, R is for radius (how far away from the axis is all of that mass?) times the angular velocity. One more variable than linear momentum.

How is balance affected with a lower center of gravity?

The lower the center of gravity the more stable of you are, girls have better balance

Slide 11, what do the parallel vertical lines and the V shape lines represent?

The parallel lines are the outside base of support left and right. The v-shape lines show that when it crosses the parallel lines demonstrate there is some angular rotation and that's as far as you can lean left or right before falling.

Slide 10, describe the difference in stability between the 2 pictures.

The picture on the left side is stable from front to back, while the picture on the right is more stable left to right

What foot do you transfer your weight toward while throwing?

Transfer from the back to front foot and keep COG low

During hitting a baseball or golf ball, what foot has most of the weight near ball contact?

Transfer the force from the back foot to the front foot

T or F The line of gravity always goes through the center of gravity.

True

How long would it take to improve an athlete's agility during training (estimate)?

You can do it instantly, if you change your technique. Very quickly, within minutes

True of False for a throwing motion

a. FALSE The arms have more mass than the trunk. b. FALSE Momentum is created first with the arms. c. FALSE Momentum in the trunk is transferred next to the legs. d. TRUE Momentum from the arm is transferred to the hand. e. FALSE Momentum from the legs is reduced as is approaches the hand. f. TRUE Body mass is reduced up the chain of body parts as momentum is transferred. g. TRUE Velocity of the body parts increase as the body part increases in mass as momentum is transferred. h. TRUE The hand is the fastest moving part of the body during a throw. i. TRUE A body part slows down to transfer the momentum to the next body segment.

Describe what happens to the center of gravity in the following:

a. Raise both arms above the head in the same position- (center of gravity moves up, not left or right) b. Abduct the arm to 90 degrees- (center of gravity would up and to the right) c. Place a back pack on your upper back- (center of gravity would go up and backwards) d. Flex your shoulders raising both arms in front of you- (center of gravity would go up.)