14. Angular Momentum & Newton's 1st Law

Question 1

What is Angular Momentum?
How do we calculate it?

Answer 1

When an object rotates, it has angular momentum,
Angular momentum is the quantity of motion

Angular momentum (H) = moment of inertia x angular velocity

○ H = Iω
○ H = mk2ω
○ Units: kg m2/s

Question 2

Explain Newtons 1st Law in relation to angular motion. (Conservation)

Answer 2

• According to Newton’s First Law, in the absence of an external torque every system remains in a constant rotational state
• So, the angular momentum in one instance should be the same as the angular momentum in another (H1 = H2)
• Conservation of Angular Momentum

Question 3

When angular momentum is conserved, there is a tradeoff between moment of inertia and angular velocity. How is that possible?

Answer 3

Question 4

How is the angular momentum maintained for this diver?

Answer 4

• Although total body angular momentum is conserved, the diver can alter their orientation in space
• Independently moving the arms can shift the axis of rotation
• The diver will start to twist and spin in the air
• The direction of the spin depends upon which arm moves

Question 5

As the diver (45 kg) leaves the platform, she becomes a projectile subject only to the influences of gravity and air resistance

Therefore, angular momentum is conserved

As she leaves the board, her radius of gyration is 0.5 m, and her angular velocity is 4 rad/s

What is her angular velocity when she assumes a tuck position,
altering her radius of gyration to 0.25 m?

Answer 5

H1 = H2
mk^2 * ω1 = mk^2 * ω
k^2 * ω1 = k^2 * ω
(0.5^2)(4) = (0.25^2)(ω)

ω = 16 rad/s

check again might be wrong

Question 6

What are the 3 components of Asymmeterical Movements?

Answer 6

Initial Movement

Compensatory Movement &

Counter-rotation

Question 7

Explain what is happening to the body during this movement.

Answer 7

Initial Movement:

• Swinging the arm at the shoulder joint will cause the whole body to rotate forward

Compensatory Movement:

• Kicking the legs forward will cause the body to rotate backwards

Counter-rotation:

• Keeps the body’s position stationary

Question 8

Whats the first muscle group to be activated here?

Answer 8

legs activate first compared to shoulders to lock body into place

Question 9

Since moment of inertia is affected by BOTH body and segment orientation, momentum must consider the entire system

What are the two terms of movemnet during angular motion?

Answer 9

Question 10

How does the body work together to acheive angular movements?

Answer 10