Angular Motion

Question 1

What is the 1st law of angular motion?

Answer 1

A rotating object remains at a constant velocity unless acted upon by an external moment.

Question 2

What is the 2nd law of angular motion?

Answer 2

An external moment produces an angular acceleration that is proportional, and in the direction of, the moment.

Question 3

What is the 3rd law of angular motion?

Answer 3

For every applied moment, there is an equal and opposite reaction moment.

Question 4

Define a moment (torque)?

Answer 4

A moment is not a force, but rather the turning effect of said force in causing rotation.

Question 5

How do you calculate a moment?

Answer 5

The product of the MAGNITUDE of a force and the PEPERNDICULAR DISTANCE of the line of action of the force to the axis of rotation.

Moment = Force * Distance

Question 6

Define the differences between an eccentric and centric force.

Answer 6

The line of action of an eccentric force does not pass through the centre of mass. It always causes rotation and, therefore, a moment. A centric force doesn’t cause rotation as the line of action is in line with the centre of gravity.

Question 7

Define a couple.

Answer 7

A pair of forces that are equal in magnitude, opposite in direction, and displaced by a perpendicular distance or moment.

Question 8

What term describes the tendency of a body to resist a change in motion?

Answer 8

Inertia

Question 9

Define Moment of Inertia.

Answer 9

The tendency of a body to resist angular motion (rotation).

Question 10

What is a resultant moment?

Answer 10

The sum of all moments acting on a body.

Question 11

What are the three methods for determining CoG?

Answer 11

Suspension, reaction board, and segmental.

Question 12

Where must the axis be positioned when determining CoG, using the segmental method, in tracker?

Answer 12

On the outside edge of the image.

Question 13

When an object is made to rotate around a new axis parallel to the first, how does the new moment of inertia relate to the moment of inertia around the first axis?

Answer 13

I = Icm + md^2

Question 14

TRUE or FALSE: segments of the human body rotate around their own centers of mass.

Answer 14

FALSE, segments of the human body rotate around joint centres.

Question 15

TRUE or FALSE: when rotating around a joint center, individual segments have a moment of inertia around an axis parallel to the joint center.

Answer 15

TRUE

Question 16

If, whilst in flight, the body rotates around the whole-body center of mass, what is the significance of individual body segments?

Answer 16

Each individual segment contributes to whole-body moment of inertia.