Lecture 7 - Angular Kinematics II

Question 1

Instantaneous centre of rotation:

Answer 1

the precise centre of rotation at a joint at a given
instant in time or given position

Question 2

In a joint, bones move relative to one another. True or False

Answer 2

True

Location of joint centre changes as position of the joint changes

Question 3

In regards to “Instantaneous centre of rotation” why is the centre of rotation changing instantaneously as the joint move

Answer 3

The centre of rotation is changing instantaneously as the joint moves because it is not a perfectly round joint

Question 4

Angular Displacement and Angular Distance

Answer 4

Same concept as difference between linear displacement and distance

ex: Picture a pendulum swinging

Question 5

Displacement:

Answer 5

difference between where it starts and ends (change in angular position)

Question 6

Angular Displacement:

Vector of Scalar:

Units:

Answer 6

The directed angular distance from initial to final angular position

A vector quantity; has both magnitude and distance

Units: degrees, radians, or revolutions

Question 7

For most calculations using an angular kinematic measure (angular velocity, displacement, or acceleration), you must convert the angle to radians

Question 8

How many radians in a complete circle

Answer 8

There are 2πradians in a complete circle

Question 9

πradians =

Answer 9

180 degrees

Question 10

1 radian =

Answer 10

57.3 degrees

Question 11

How do you get from degrees to radians

Answer 11

To get from degrees to radians, take the angle in degrees, and divide it by 57.3

Or,

take the angle in degrees, multiply it by π and then divide by 180 degrees

Question 12

This is a unitless unit because…

Answer 12

= Angle (rad) = arc length (m) / radius(m)

= 2πr X fraction of a rev / r

= 2π X fraction of a rev

The metres cancel out, so it becomes unitless

Since both length and radius are in the same units, they both cancel, and the resulting radian is unitless

Question 13

90 degrees = _____ radians = ____ revolution

180 degrees = ______ radians = ______ revolution

270 degrees = _______ radians = _______ revolution

360 degrees = ______ radians = ________ revolution

Answer 13

90 degrees = π/2 radians = 1⁄4 revolution

180 degrees = π radians = 1⁄2 revolution

270 degrees = 3π/2 radians = 3⁄4 revolution

360 degrees = 2π radians = 1 revolution

Question 14

Direction of Angular Motion defined in terms of ……

Answer 14

Defined in terms of direction of rotation around the axis of rotation

Question 15

Is Counterclockwise(going towards y-axis) positive or negative ?

Answer 15

Counterclockwise is defined as a positive rotation (going towards y-axis)

Question 16

*You can draw an angular motion vector as a straight line in the direction of the axis of rotation using the right hand rule

Question 17

Right hand rule:

Answer 17

the procedure for identifying the directions of an angular vector

Fingers curl in the direction of motion

Thumb indicates direction of vector (it is really the axis)

Question 18

Angular speed (scalar) =

Units:

Answer 18

angular distance/change in time (this is scalar)

deg/s, rad/s, rev/s, & rpm

Question 19

Angular velocity (vector) =

Units:

Answer 19

angular displacement/change in time (this is a vector)

deg/s, rad/s, rev/s, & rpm

Question 20

Angular acceleration =

Units:

Answer 20

change in angular velocity/change in time (vector)

Units: deg/s^2, rad/s^2, & rev/s^2

Question 21

Average Vs. Instantaneous Angular Kinematic Relationships

Average:

Answer 21

the average distance from stop to start

Question 22

Average Vs. Instantaneous Angular Kinematic Relationships

Instantaneous:

Answer 22

plotting individual movements (slope)

Question 23

READ OVER “Kinematic Parameters: Vectors” AND “Kinematic Parameters: Scalars” ON LAST PAGE OF NOTES