ch 6 study
Recognize the difference between an ABSOLUTE and a RELATIVE angle position.
Be prepared to identify whether a limb angle position is an absolute or relative angle position.
Absolute- if the other line or plane is fixed or immovable relative to the earth (orientation to angle line) such as angle of forearm to horizontal plane
Relative- if the other line/ plane can move (it is NOT fixed) such as angle of forearm to upper arm
Recognize the three ways to describe an angle.
Recognize equivalences between degrees, fractions, and radians and be prepared to do easy conversions.
90 degrees = pie/2= 1/4 revolution
180 degrees= pie= 1/2 revolution
270 degrees= 3 pie/ 2= 3/4 revolution
360 degrees= 2pie= 1 revolution
Recognize the definition of angular displacement and how the direction of angular displacement is described.
Angular displacement- change in ABSOLUTE angular position (angle formed between final and initial position of a rotating line)
Direction- clockwise= negative
counter clockwise= positive
Since the direction of angular displacement depends upon your VIEWPOINT identify two bits of information necessary to reduce confusion. Be prepared to identify the direction of angular displacement given examples of movement and the conventions of the "right-hand rule"
1. Identify the axis of rotation 2. identify the plane
1. laterally abduct left arm ( from anatomical position)- clockwise = negative angular displacement
2. laterally abduct right arm (from anatomical position)- counterclockwise= positive angular displacement
Identify the mechanical disadvantage humans have in producing torque.
muscle must produce very LARGE force to lift modest (relatively light) loads
Identify the mechanical advantage of having muscle insertions close to the joint's axis of rotation.
muscle contracts ONLY a short distance to produce a LARGE movement (linear displacement) at the end of a limb
Define angular velocity.
Identify three units of measurement for angular velocity
Angular velocity- the rate of change in angular displacement
3 units- rads (radiance per second), degrees per second, and rpm (rotation per minute)
Is angular velocity a vector quantity?
How do you determine the direction of angular velocity?
direction same as angular displacement (counter clockwise= negative)
Recognize definitions of average angular velocity and instantaneous angular velocity.
Average AV- need to determine HOW LONG it takes for something to rotate through a certain angular displacement
Instantaneous AV- HOW FAST something is spinning at a specific instant in time
recognize sports skills where each factor is the most important measurement
Average AV- most important in gymnastics, diving, figure skating
instantaneous AV- most important in softball, baseball
Tennis- how fast will travel based on angular velocity of bat or racket at instant of impact
Under the label angular linear velocity identify the TWO advantages of using implements as extensions of the performers limbs.
1. Implements amplify the motion (displacement) of the limbs
2. implements enable us to impact faster linear velocities to the ball (pack, shuttlecock)
To explain the relationship between angular and linear velocity which accounts for the advantages experienced with implements, identify how different points (positions) on a swinging implement are the same or different in regard to - angular displacement, angular velocity, linear speed, and linear displacement.
All points on a swing implement are:
SAME FOR: 1. angular displacement 2. average angular velocity
Different for: 1. longer ARC length travelled 2. faster linear speed (farther from axis) 3. longer linear displacement
Explain each of the following questions using the relationship between linear and angular velocity.
Why can you hit a golf ball farther with a wood than a shorter heavier IRON club
The ball is hit harder.
The ball travels FARTHER due to faster linear velocity and instantaneous angular velocity.
Why can you hit a baseball farther with a longer bat?
By the time the ball is hit in tennis, golf, or baseball, what is the EFFECTIVE (real) length of the radius of the racket, club, or bat?
1. longer baseball bat will generate faster instantaneous angular velocity
2. the effective radius is LONGER than the rocket, club, or bat length
In the last question where is the axis of rotation upon ball impact?
What enables our hands and feet to move at faster linear velocities THAN the much slower muscle contraction velocities initiating the movement?
Its within the body- often between the shoulders or at shoulder joint/
At the end of limb, linear velocities has been AMPLIFIED
Define angular acceleration.
Identify three units of measurements for angular acceleration.
Is angular acceleration a vector quantity?
How do you determine the direction of angular acceleration?
1. the rate of change of angular velocity
2. radian/sec/sec or degrees/ sec/ sec or revolution/min/min
3. determine direction, use the right hand rule
Identify the THREE occurrences of angular acceleration
1. spins faster and factor
2. spins slower and slower
3. spinning object axis of rotation changes direction
What happens to the linear velocity of a point on a spinning object when the angular velocity of that SPINNING object increases?
What is tangential acceleration?
1. linear velocity increases
2. the component of linear acceleration tangent to the circular path on a rotating object
Does a point on a rotating object experience any linear acceleration if the object spins at a constant angular velocity (with no angular acceleration) WHY
Yes, even though it doesn't speed up or slow down the point is constantly changing direction as it follows a circular path.
What is the force responsible for this effect?
In which direction does this force act?
1. centripetal force (caused by centripetal or radial acceleration)
2. force is directed toward the axis of rotation. Therefore centripetal acceleration is LINEAR acceleration.
How does a performer exert centripetal force when running a curve or swinging a hammer?
When must the centripetal force be greatest- around an outside or INSIDE
Which produces the greatest centripetal force a hammer throw with a SHORTER OR LONGER throw chain
on a curve, shoes use friction. On hammer, pull is centripetal force.
Define the anatomical reference position.
Stand erect, feet aligned parallel, toes forward, straight arms at sides , plans forward.
SAGITTAL PLANE also called the...
This plane divides the body into...
Right and Left parts
FRONTAL PLANE also called the...
This plane divides the body into..
coronal or lateral
Anterior (front) ad posterior (back) parts
TRANSVERSE PLANE also called the...
This plane divides the body into
Superior and inferior
What is a cardinal plane
Plane passing through midpoint or CG