Bionics

Warm-Up Do you think technological advances in prosthetics give an unfair advantage in sports?

Warm-Up Videos Hugh Herr Previous Scientist of the Month (last semester) Double amputee MIT professor of biomechanics Rock climber http://www.youtube.com/watch?v=g-26_y30Tww During this next video, towards the end, Hugh talks about one of Newton’s Laws – which one is it? http://www.youtube.com/watch?v=8AoRmlAZVTs

Which Law did Hugh Herr Mention? Newton’s Third Law: Action/Reaction

Moving Forward Hugh mentioned that in his lab they are trying to understand how our natural bodies function in order to build technological models that function the same way. Now that we have learned one very important application of physics and biology – prosthetics – we are going to spend some time understanding how our limbs generate movement.

Archimedes “Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.” Take a moment to identify unknown words in this expression. What do you think Archimedes is trying to say here?

“Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.”

What is a lever? Simple machine designed to increase velocity or move high inertia objects. Who remembers what inertia is?

Components of a Lever Resistance (load) Effort or Applied Force Fulcrum (pivot) dl = resistance arm de= force arm

Resistance Arm (RA) – distance from where resistance acts to the fulcrum Force Arm (FA)– distance from where a force is applied to the fulcrum

“Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.”

First Class Fulcrum lies between R and F. FA can equal RA, but it doesn’t have to This would create a balance FA < RA – produces greater speed and range of motion FA > RA – produces greater output of force Force Magnifier Designed for balance

Second Class Resistance lies between fulcrum and applied F. FA and RA are on the same side of the lever. FA>RA (always) Magnifies applied force

Third Class F lies between the R and fulcrum FA < RA F is always greater than the Resistance Distance magnifier.

Third Class Generates speed over distance at point of resistance. Longer the lever the longer RA will be and thus more speed produced to resistance (load) Pitching: Increase should muscles increases F applied, which increases velocity of arm and transfer of momentum to the ball.

Warm-Up What are the 3 classes of levers? Which class is always a force magnifier? Which class is always responsible for increase in speed and range of motion. Which class of lever can be both a force magnifier and a speed/range of motion magnifier?

Classes of Levers First Second Third Fulcrum lies between the resistance and applied force. Resistance lies between fulcrum and applied force. Force lies between the resistance and the fulcrum.

Expanding Summary Pick a lever class. Draw a pictorial summary for the lever. Using your visual summary to help you, write a 5-8 word summary for your lever class. Find other students who wrote about the same class lever as you.

Expanding Summary Share your summary with someone who did the same class lever as you. Discuss everything you learned about this lever with your group. Write a 25 word summary about your class of lever.

Which class do you think is most common in the human body? Levers in the Body Which class do you think is most common in the human body?

Levers in the Body Bones represent the lever bars Joints are the axes (fulcrum) Resistance – may be the weight of the bones, body, or an applied load Effort (applied force) - Muscles contract to apply force at point of insertion Note: you have to pay attention to the insertion site of muscles, some are at the joint (triceps), but some aren’t (biceps).

First Class Levers in the Body

Second Class Levers in the Body

Third Class Levers in the Body

Summaries Add 1-2 sentences to your summary that explains how your class of lever is found in the human body.

Mechanical Advantage Ratio between Force Arm and Resistance Arm. MA = FA/RA MA > 1 Mechanical advantage in force (amplification of force) First and second class levers MA < 1 Mechanical advantage in speed and range of motion First and Third class levers FA must always be greater than resistance – no mechanical advantage

MA in the Body Origin and insertion of muscle determines the mechanical advantage. The further the insertion point from the joint, the less force required

Torque Turning force T = Fd Greater the force, greater the torque Greater the distance, greater the torque In order to move an object, the T generated by the body must be greater than the torque generated by R.

Torque in the Body Our bodies are built for speed and range of motion at the expense of force. Short FA and long RA require great muscular strength to produce movement. Biceps: FA = 1-2 in Triceps: FA < 1in

Thought Question How might our knowledge of mechanical levers and their application in the body impact the design and functionality of a prosthetic (keep in mind, not all prosthetics are limbs)?