Week 3 - forces

Question 1

Define force

Answer 1

An influence that can change the motion of an object

Question 2

Define vector

Answer 2

A force that has both magnitude and direction

Question 3

Define tensile forces

Answer 3

Opposing eg. tug o war

Question 4

Define compression force

Answer 4

Pushing together eg. spring
- muscles + tendons not well equipped for this

Question 5

Shear force

Answer 5

Friction eg. sled pull

Question 6

What are the 3 force combinations making up muscle force

Answer 6

Internal force, direct contact force, tensile force

Question 7

What are the 2 force combinations making up ground reaction force

Answer 7

External force, direct contact force
- equal magnitude, opposite direction to force applied to ground

Question 8

Describe Newton’s first law

Answer 8

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

Question 9

Describe Newton’s second law

Answer 9

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

Question 10

Describe Newton’s third law

Answer 10

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

Question 11

Differentiate b/t a scalar + vector

Answer 11

Scalar = no direction eg. speed
Vector = magnitude + direction eg. velocity

Question 12

List + describe the 4 components of a vector as seen on a free body diagram

Answer 12

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

Question 13

Example of first class lever

Answer 13

Atlantooccipital joint (neck)
- load = weight of head
- fulcrum = atlanto-occipital joint
- effort = cervical extensor muscle

Question 14

Example of second class lever

Answer 14

Calf raise
- fulcrum = axis of MTP joint
- load = weight of leg
- effort = gastroc/soleus force

Question 15

Example of third class lever

Answer 15

Bicep curl
- fulcrum = elbow joint
- effort = biceps brachii muscle force
- load = weight of arm

Question 16

State the mechanical advantage for each lever class

Answer 16

1st = greater than or less than 1
2nd = always greater than 1
3rd = always less than 1