Chapter 9 Flashcards
What is the difference between kinetics and kinematics?
Kinematics studies motion (displacement, velocity, acceleration) without considering forces, while kinetics focuses on the forces and torques that cause motion. Kinematics explains “what happens,” and kinetics explains “why it happens.”
What two pieces of information are provided by the net joint moment?
1 - the sense
2 - the magnitude (referring to muscular effort)
How does point mass idealization represent an object?
The point mass idealization represents an object as a single point in
space. While the object’s geometry is ignored, the object’s mass is considered.
How does rigid body idealization represent an object?
A rigid body has mass and geometry, however, the object may not deform (or is assumed not to deform).
What are the steps to draw a free body diagram of a rigid body?
1 - identify your coordinate system
2 - draw each rigid body independently
3 - identify and draw the inertial characteristics (ie centre of mass)
4 - draw the moments and forces acting on the rigid body
What two conditions must exist for there to be static equilibrium of a rigid body?
Condition 1 states that velocity must equal zero, therefore acceleration is zero. To
achieve this condition, the sum of all forces acting on a rigid body equals zero.
Condition 2 states that angular velocity must equal zero, therefore angular
acceleration is zero. To achieve this condition, the sum of all moments (torque) acting of a rigid body equals zero.
Define a moment of force?
The tendency for a force to turn or rotate a rigid body about a point (torque, moment).
What are the units for a moment of force?
Nm
Why might it be helpful to know the centre of mass (COM) of an individual?
The centre of mass of an individual may give insight into their level of stability.
For example, older people tend to lose muscle mass in their lower extremities. This could raise their centre of mass and in turn make them less stable. This is important for injury prevention and whatnot.
Where is the COM of the foot?
50% between the lateral and medial malleoli and the metatarsal heads
The cross product changes the magnitude of the vector - true or false?
False, the cross products changes the sense of the vector.
What is a compensatory movement strategy?
After an injury, avoiding using certain muscles and compensation by using others.
What is a common compensatory movement strategy for those recovering from ACL injuries?
What net joint moment can measure this?
Quadriceps avoidance strategy.
Knee extensor net joint moment.
