Principles 2- WK1 (Ch 1+4 ) Flashcards
Explain Newton’s 3 Laws of Motion:
1st law of inertia: an object will remain at rest unless acted upon by an external force
2nd law of acceleration: sum of forces=mxa; acceleration of a body is proportional to the force causing it
3rd law of action-reaction: for every force there is an equal and opposite directed force
Define Center of Mass:
The point at which mass is evenly distributed in all directions in a body; same as center of gravity
If a cuff weight is added to the wrist then what happens to the extremities center of mass ? How does that affect the muscles that lift the arm ?
- shifted downards
- lifting the arm may require that more work be done by the muscles
What would happen to the body’s overall CoM if a person had a below knee amputation on the right leg ?
it would shift left and up so as to ‘re-center’ the CoM.
What is the relationship between CoM and Mass moment of inertia ?
Mass moment of inertia: quantity indicating resistance change in angular velocity
As individual extremities centers of mass approach a pivot point the lesser the mass moment of inertia, thus having more rotational velocity around said pivot
How does the acceleration of an object change if the force to move it remains constant but the mass of the object decreases ?
F= decrease mass x increased acceleration; increased acceleration
How would the quadriceps muscle force need to change when going form lifting a 5 pound weight during knee extension to lifting a 10 pound weight if the movement speed remained the same ?
increased F= increased mass x acceleration; force would need to increase
Compare joint reaction force to ground reaction force.
JRF: caused in reaction to other forces acting on the joints; joints push back up
GRF: force coming upward from the ground as force is directed into the ground from the body, Newton’s third law
What is a vector ? What characteristics apply to all force vectors ?
quantity that is specified by magnitude and direction
-magnitude, spatial orientation, direction, point of application
- angle of muscle insertion
How can a joint be in static linear equilibrium ?
- When the sum of forces acting on the joint are equal to zero
- internal force and external force + JRF = 0
How can a joint be in static rotary equilibrium ?
- If internal torque and external torque=0
- When the sum of forces acting on the joint are equal to zero
Define moment arm. How does moment arm affect the ability of a force to rotate a segment ?
- perpendicular distance between the axis of rotation and the force
- a longer moment arm provides more leverage, creating a greater torque
What is a force couple ?
when two or more muscles produce forces in different linear directions but same rotary direction.
Describe all 3 classes of levers and their mechanical advantages.
1st class: like a seesaw; AoR between Ext. force and Int. force ( MA= <1, >1, or 1 )
2nd class: like a wheel barrow; AoR at one end with the Ext. force and EMA between the Int. force and IMA and the AoR ( MA>1)
3rd class: IMA and IF between EMA and EF and AoR (MA<1)
Compare the mechanical advantage and lever system of the gastrocnemius muscles with the deltoid shoulder muscles. Which system allows a greater arc of motion or angular displacement ? Why ?
… TBD
