Lesson Six - Levers & Free Body Diagrams

Lesson 6
Quote of the day...
“It is the mark of an educated mind to be able
to entertain a thought without accepting it.”
- Aristotle
General Feedback From Phase 1
 Questions & Concerns:
 The use of class time
 Problems with technology
 Formatting / Independent study skills
 Things Done Well
 Anatomical terms and descriptive detail
Phase 1 Feedback
 Areas for Improvement
 Repetition of similar observations
 Avoid using LEFT & RIGHT terminology
 Dominant hand + Non-dominant hand
 Lead foot + Trail foot
 Weight bearing leg + Non-weight bearing leg
 Front foot + Back foot
 What to look for? Where do I find it?
 P. 231 – First 3 Principles of Biomechanical Analysis
Review Key Concepts
1. What are Newton’s Three Laws of Motion?
2. What are the different types of motion?
3. Linear & Rotational Motion Terminology
Key Terms
Linear Motion
Rotational Motion
- Displacement
- Velocity
- Acceleration
- Force
- Mass
- Angular displacement
- Angular velocity
- Angular acceleration
- Torque
- Moment of inertia
Moment of Inertia
Recall the relationship between Mass, Force and
 The moment of inertia describes the distribution
of mass in relation to it’s distance from the axis of
 The further the mass is from the axis of rotation,
the greater the moment of inertia (therefore the
harder it is to cause it to spin or stop it from
 The closer the mass is to the axis of rotation, the
easier it is to rotate it or stop it from rotating
Moment of Inertia Continued
Linear Motion:
Acceleration: Force
Rotational Motion:
Moment of Acceleration: Torque
Moment of Inertia
 Key Idea: The larger the moment of inertia,
the more difficult it is to change the state of
motion of that object.
Small Moment of Inertia
Large Moment of Inertia
Lever Systems
Every moveable bone in the human body, acting
alone or in combination with others, is part of a
lever system that facilitates movement.
Components of Lever Systems:
1) Fulcrum (axis) – the pivot about which a lever turns
2) Load (resistance) – the amount of weight placed on
a lever system
3) Force (muscle) – the pull acting in opposition of the
Lever Systems
Class 1 Lever: (Teeter-totter)
 The fulcrum is located between the force and
the load
Example – the neck moving from a position of
flexion to extension
Lever Systems
Class 2 Lever: (Wheelbarrow)
 The resistance is between the force and the
Example – the ankle joint. The gastrocnemius
muscle pulls on the calcaneus to plantar flex
the foot
 Second class levers can lift the largest
amount of weight
Lever Systems
Class 3 Lever: (Snow Shovelling)
 The force is between the fulcrum and the
 The most common lever system in the human
Example – the bicep-elbow complex
 With this lever system there is a
speed/muscle trade-off
 Handout - Labelling Lever systems:
Free Body Diagrams
Simplified representations of the body, and forces acting
upon it
Construct a Free Body Diagram:
1) Isolate the body or interest
2) Draw all external forces acting on the body
3) Label the center of mass and base of support
4) Identify and fully label the lever systems in use
5) Show direction of motion for the major limbs in use
Website practice - http://www.physicsclassroom.com/class/newtlaws/u2l2c.cfm
 Review Phase 1 of your sport skills analysis:
 For each phase, assess where the fulcrum, load
and force are located.
 What type of lever system is causing movement?
 Come to LAB tomorrow with Phase 1 and
homework questions completed

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