Week 3 - forces Flashcards
Define force
An influence that can change the motion of an object
Define vector
A force that has both magnitude and direction
Define tensile forces
Opposing eg. tug o war
Define compression force
Pushing together eg. spring
- muscles + tendons not well equipped for this
Shear force
Friction eg. sled pull
What are the 3 force combinations making up muscle force
Internal force, direct contact force, tensile force
What are the 2 force combinations making up ground reaction force
External force, direct contact force
- equal magnitude, opposite direction to force applied to ground
Describe Newton’s first law
Inertia -
- an object will remain at rest or at a constant velocity unless acted upon by an unbalanced force
- resistance to movement is directly proportional to mass
Describe Newton’s second law
Acceleration -
- the acceleration of an object is proportional to the net unbalanced force acting upon the object
eg. object w/ small mass accelerates more than large object w/ same force applied
Describe Newton’s third law
Action-reaction -
- When a mass makes (or is already in) contact w/ another mass, there will be a reaction force that is equal in magnitude but opposite in direction
- for every action there is an equal and opposite reaction
Differentiate b/t a scalar + vector
Scalar = no direction eg. speed
Vector = magnitude + direction eg. velocity
List + describe the 4 components of a vector as seen on a free body diagram
Point of application = where the force acts upon the body ie. where line shows
Action line = line along which force acts ie. location of line
Magnitude = the size of the force ie. length of line
Direction = the direction of the force ie. direction arrow points
Example of first class lever
Atlantooccipital joint (neck)
- load = weight of head
- fulcrum = atlanto-occipital joint
- effort = cervical extensor muscle
Example of second class lever
Calf raise
- fulcrum = axis of MTP joint
- load = weight of leg
- effort = gastroc/soleus force
Example of third class lever
Bicep curl
- fulcrum = elbow joint
- effort = biceps brachii muscle force
- load = weight of arm
State the mechanical advantage for each lever class
1st = greater than or less than 1
2nd = always greater than 1
3rd = always less than 1
