30. What class lever is this? What downward force must be exerted at F to balance the downward torques of R1 and R2? 1' 2' 9 lbs. 1 lbs. 3' R1 F R2
31. What class lever is this? What downward force must be exerted at F to balance the downward torques of R1 and R2? 1' 2' 5 lbs. 1 lbs. 4' F R1 R2
32. What class lever is this? What upward force must be exerted at F to balance the downward torque of R? What is the mechanical advantage of this lever? 9' 9' 6 lbs. F R
33. What class lever is this? What upward force must be exerted at F to balance the downward torque of R? What is the mechanical advantage of this lever? 3' 2' 5 lbs. F R
34. What class lever is this? What upward force must be exerted at F to balance the downward torque of R? What is the mechanical advantage of this lever? 5' 5' 5 lbs. F R
35. What class lever is this? What upward force must be exerted at F to balance the downward torque of R? What is the mechanical advantage of this lever? 2' 4' 2 lbs. F R
Forces are vector quantities - have direction and magnitude Physical Movement - velocity, acceleration, deceleration Weight (both mass and pull of gravity) - pounds, Newtons Force - pounds, Newtons Stress - pascal Friction - Work Arrows indicate vectors - #’s usually accompany vectors showing amount of force. Vectors can be added or subtracted if working in the same line Rugby scrum – Five Guys pushing – 70/60/30/40/50 against four guys 100/75/75/75 250 against 325 - four guys win
Magnitude – length of vector indicates “size” Direction – which way it is acting Sense – is it positive (muscle) or negative (resistance) Point of Application – Where it is acting
Example: Movement of arms, legs is rotatory A B
Example: Draw rectangle on board 3 by 4 with internal line 5 3 N 4 N 5 N
Demonstrate with levers
Torque is an expression of effectiveness of a force in turning a lever system. Such as opening a car door Using a lever to lift something - longer the force arm less force needed – demonstrate with levers (Aristotle moving the Earth) Clinical application - passive stretching - demonstrate with elbow extension points at wrist and midway to elbow
Demonstrate with lever and fulcrum. In balance - forces and force arms equal Or in other words if equal weight on each side Think of a see saw -can adjust length of arms
Demonstrate - have fulcrum at one end, resistance in middle and use “fish scale” to show force used Brachioradialis origin – proximal 2/3 of the lateral supracondylar ridge of the humerus and lateral intermuscular septum Inserts - lateral side of the base of the styloid process of the radius
Demonstrate again with the force applied in the middle of the lever. Is more force required if the lever is longer and the resistance further away?
Demonstrate with different lengths of the force arms and resistance arms, to maintain equilibrium. Do calculations - see examples from past. Go back to type of levers 1 st class show amount of force with one pound on one end 2 nd class – resistance is closer to the fulcrum RA – 1ft. FA – 2ft. Resistance is 1# RA x R = FA x F 1 x 1 = 2 x (answer is .5 #) 3 rd class – force closer to fulcrum R equal 1# RA - 2 ft. FA – 1ft RA x R = FA x F 2 x 1 = 1 x (answer is 2#)
Demonstrate with lever and fulcrum - 1 st class lever (R1A x R1) + (R2A x R2) = FA x F (9 x 1) + (3 x 1) = 3 x (answer or Y) 12 = 3 x (Y) or answer is 4 #
Demonstrate with lever and fulcrum 1 st class lever (R1A x R1) + (R2A x R2) = FA x F (5 x 1) + (3 x 1) = 4 x (answer or F) 8 = 4 x (F) or answer is 2 #
Second class lever – (RA x R) = FA x F (9 x 6) = 18 x (answer or F) 54 = 18 x (F) or answer is 3 # MA = FA/RA MA = 18/9 or 2
Second class lever – (RA x R) = FA x F (5 x 3) = 5 x (answer or F) 15 = 5 x (Y) or answer is 3 # MA = FA/RA MA = 5/3 or 1.67
Third class lever – (RA x R) = FA x F (10 x 5) = 5 x (answer or F) 50 = 5 x (F) or answer is 10# MA = FA/RA MA = 5/10 or 0.5
Third class lever – (RA x R) = FA x F (6 x 2) = 2 x (answer or F) 12 = 2 x (F) or answer is 6 # MA = FA/RA MA = 2/4 or 0.5
Example in Brunnstrom - page 36 torque changes for external force – Example is Brunnstrom page 36 picture lifting weight - moment arm is essentially the resistance arm closer to the body less force a person is lifting. -- Overhead # 2 Moment Arm - exists for a moment - Overhead # 3 Example page 62 for internal force or force of muscle - Overhead # 4 Page 73 and 77 of Roberts