14. Moment of Inertia

Question 1

1st Law

What is The Law of Inertia?

Answer 1

Every object has a desire to remain in a static state

Question 2

What is The Law of Inertia as it pertains to Linear Motion?

Answer 2

Every body persists in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled tochange its state by force impressed

Question 3

What is The Law of Inertia as it pertains to Angular Motion?

Answer 3

The Law of Inertia in angular motion states that an object will maintain its state of rotational motion or rest unless acted upon by an external torque.

Question 4

What is Moment of Inertia?

Answer 4

Moment of inertia is the name given to rotational inertia, the resistance of any physical object to any change in its angular state of motion

The moment of inertia is specific to a chosen axis of rotation

Inertia = Linear : Moment of Inertia = Rotational

Question 5

How do we calculate the moment of inertia?

Answer 5

● Moment of Inertia (I) = (mass) x (radius of gyration)2
● I = mk^2
● Units: kgm^2

Question 6

What is the radius of gyration?

Answer 6

The radius of gyration is the linear distance (measured in meters) between the axis of rotation to a point where the body mass is concentrated

Question 7

What is The principal moment of inertia?

Answer 7

The principal moment of inertia examines the amount of resistance to change relative to one of the principal axes of the body

Question 8

How difficult it is to move the body in a particular direction?

Reference the 3 Planes of Motion.

Answer 8

Transverse Plane: (longitudinal/horizontal )

• lowest moment of inertia (easy to shake head no)

Saggital Plane: (Medio-lateral )

• Moderate moment of inertia (harder to nod head yes)

Frontal Plane (Anterio-Posterior )

• Greatest moment of inertia (lateral flelxion)

Question 9

What is rotational inertia affected by?

Answer 9

Rotational inertia is affected by the distribution of mass in a system

Question 10

To move, we must overcome inertia. How can we decrease the moment of inertia to make it easier to move?

Answer 10

Decreasing the radius of gyration, makes it easier to move by decreasing the moment of inertia

Question 11

Imagine you had to carry the heavy object pictured below. What is the best method of carrying the item?
Explain your answer.

Answer 11

Technique 2:

Less torque is required because the radius of gyration is lower and thus moment of inertia is lower