Angular Kinetics

Question 1

Angular Kinetics

Answer 1

Angular inertia or rotary inertia

-the property of an object to resist changes in its angular motion

Question 2

Angular inertia

Answer 2

is affected by:

• the mass of an object
• the distribution of mass of an object relative to the axis of rotation

Question 3

Moment of inertia

Answer 3

the quantification of angular inertia
I = mk^2
I = moment of inertia
m = mass of object
k = distance from the mass to the axis of rotation (radius of gyration)

Question 4

manipulating the moment of inertia (human)

Answer 4

influenced by changing the orientation of the limbs in relation to the rest of the body (i.e. figure skater pulling arms in towards body to spin faster)

Question 5

Pole Vaulting

Answer 5

• builds kinetic energy in the run up
• stores elastic potential energy as he exerts force on the pole to bend it
• swinging his body up, he reduces the rotation of the pole as well as increases his rotation about the pole
• now the pole pushes back as it starts to straighten and he gains gravitational potential energy as he loses the elastic potential energy
• then he releases the pole and falls to his doom

Question 6

Angular momentum

Answer 6

the tendency for an object to remain in angular motion
L = I Ω
L = angular momentum
I = moment of inertia
Ω = angular velocity

Question 7

conservation of angular momentum

Answer 7

people ( or non-rigid objects) can change their moment of inertia and thus their angular velocity while maintaining the same angular momentum

Question 8

angular momentum of the human body

Answer 8

is dependent on the sum of the angular momentum of the limbs

Question 9

Angular interpretation of Newton’s 1st law

Answer 9

angular momentum of an object remains constant unless a net external torque is exerted on it
-if the moment of inertia changes, the angular velocity of the object will change to maintain the same momentum

Question 10

Angular momentum of a hurdler

Answer 10

while jumping, the arm and trunk turn in order to balance that angular momentum of the leg
-keeping the trailing leg close to the body minimizes the angular momentum because there is a small moment of inertia

Question 11

Newton’s 2nd Law: The law of angular acceleration

Answer 11

a torque (moment) applied to a body causes an angular acceleration of that body of a magnitude proportional to the torque, in the direction of the torque (moment), and inversely proportional to the moment of inertia

Question 12

the greater the inertia of an object…

Answer 12

the more force or torque is required to make it accelerate

Question 13

Angular and Linear (momentum??) formulas

Answer 13

Angular: M = Iα
M = moment (torque)
I = moment of inertia
α = angular acceleration

Linear: F = ma

Question 14

Newton’s 2nd Law angular (it’s literally the entire slide on the answer so don’t feel bad if you don’t get it, but then it’s also pretty simple so maybe you should feel bad… :/ )

Answer 14

net external force is exerted on an object at a distance from the axis of rotation, the object will accelerate angularly in the direction of the net external torque, and its angular acceleration will be proportional to the net external torque and inversely proportional to its moment of inertia

Question 15

Angular impulse

Answer 15

a measure of torque applied for a certain amount of time
Angular impulse = Torque X time
J = Mt

Question 16

In sports, changes in momentum happen in… (hint: human caused changes)

Answer 16

• the entire body
• a piece of equipment
• an individual body part

Question 17

Maximizing the time the torque is applied

Answer 17

Diving: maximize the time that the force is applied by having a large moment of inertia but then quickly minimizing the moment of inertia to increase his/her angular velocity

Question 18

changing an objects angular velocity (increase momentum) from rest requires that we produce…

Answer 18

according to impulse (J = Mt),

a large torque over a short period of time or a small torque over a long period of time

Question 19

Newton’s 3rd law: the law of angular reaction

Answer 19

every torque is accompanied by a reaction torque, equal in magnitude and opposite in direction