Angular Kinetics 2

Question 1

What is angular force?

Answer 1

• eccentric force: away from CoG
• turning effect –> torque
• a force tending to cause rotation around a fixed point

Question 2

The shorter the moment arm, the ____ (more/less) torque on the system.

Answer 2

less

Question 3

Describe levers.

Answer 3

• hinged, rigid structures

- hinged point = axis of rotation (fulcrum)

Question 4

What is the force causing motion in a lever called?

Answer 4

F (or motive force: MF)

Question 5

What is the force acting in opposition in a lever called?

Answer 5

R (or resistance force: RF)

Question 6

Where is the fulcrum, F (motive force), and R (resistance force) in a 1st class lever?

Answer 6

• fulcrum/axis in middle
• downwards motive force on one side
• downwards resistance force on the other

Question 7

Give examples of 1st class levers.

Answer 7

• see-saw

- atlanto-occipital joint

Question 8

Where is the fulcrum, F (motive force), and R (resistance force) in a 2nd class lever?

Answer 8

• fulcrum/axis on one side
• upwards motive force on the other side
• downwards resistance force in the middle

Question 9

Give examples of 2nd class levers.

Answer 9

• wheelbarrow

- ankle when on tip toes

Question 10

Where is the fulcrum, F (motive force), and R (resistance force) in a 3rd class lever?

Answer 10

• fulcrum/axis on one side
• upwards motive force on the same side
• downwards resistance force on the other side

Question 11

The greater the forces acting on a lever system, the ______ (greater/less) tendency to cause rotation and the _____ (greater/less) angular rotation.

Answer 11

• greater

- greater

Question 12

The greater the distance between the two forces (F and R) in a lever system, the _____ (greater/less) the turning effect (torque).

Answer 12

greater

Question 13

A lever of any class will balance when…

Answer 13

the product of the force arm (FA, from F to fulcrum) and the force (F) is equal to the product of the resistance arm (RA, from R to fulcrum) and the resistance (R):
FA x F = RA x R

Question 14

Mechanical advantage (MA) increases as…

Answer 14

the FA gets larger than the RA

Question 15

Shorter levers are ______, while longer levers are ______ .

Answer 15

• faster

- stronger

Question 16

Describe the ARF where the lever is an arm held at a 90 degree angle holding a dumbbell.

Answer 16

• Axis of rotation (fulcrum): elbow
• Resistance Force: dumbbell weight x gravity (Newtons)
• Motive Force: bicep muscular contraction upwards

Question 17

What is angular inertia?

Answer 17

property of an object to resist changes in its angular motion

Question 18

Name the 2 factors that affect angular inertia.

Answer 18

• mass

- distribution of mass

Question 19

Ia would be greater when:

Answer 19

• greater mass (heavier)

- mass is further away from the axis of rotation

Question 20

What is the moment of inertia (I)?

Answer 20

quantity of angular inertia

Question 21

Distribution of mass is also referred to as…

Answer 21

radius of gyration (k)

Question 22

What is the radius of gyration (k)?

Answer 22

Distance from axis of rotation to a point at which the mass of the body can theoretically be concentrated without altering the inertial characteristics of the rotating body

Question 23

What is angular momentum (H)?

Answer 23

the product of the angular inertial property (moment of inertia) and angular velocity

Question 24

What are the 3 factors that affect angular momentum (H)?

Answer 24

• mass
• distribution of mass
• angular velocity

Question 25

Is mass, length (radius of gyration), or angular velocity more important in calculating angular momentum?

Answer 25

length (radius of gyration)

Question 26

What is the conservation of angular momentum?

Answer 26

the total angular momentum of a given system remains constant in the absence of external torques

Question 27

Does gravity affect the angular momentum of a body rotating in the air? Why or why not?

Answer 27

• no

- gravitational force acts through the CoG, therefore, there is no torque (eccentric force)

Question 28

Can an athlete add angular momentum once their body has left the ground?

Answer 28

no

Question 29

In order to speed up or slow down rotation once their body has left the ground, the athlete must…

Answer 29

redistribute mass (lengthen or shorten k – tuck legs in, fold into pike, etc.)

Question 30

Once the body has left the ground, _____ must change to conserve angular momentum.

Answer 30

angular velocity (ω)