Wheels and Axles | Pulleys | Cams | Incline Plane | Gears, Belts, Chains
Wheels and Axles
- Examples
- Can opener, volleyball net crank, tricycle, old bicycle.
- Example of wheel and axle-like arrangements in body
- shoulder internal rotation with elbow bent during overhand throw or tennis serve
- forearm pronation in badminton
- Mechanical advantage
- Radius of wheel/Radius of axle
- Increased range of motion advantage during throwing movement.
Pulleys
- Function
- Main function of pulley system is to change effective direction of applied motive force
- Compound pulleys allow a greater load to be hoisted through a shorter distance
- Split pulleys allow a single load to be lifted with two independently acting motive forces
- Example
- cable pulley weight training machines
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- Pulley-like arrangements in body
- Patella at knee
- pulled between the condyles of femur
- patellar tendon - patella - quadriceps arrangement
- quadriceps muscle pull proximally toward their bellies
- yet knee extension (from flexed position) cause leg to move in opposite direction
- Lateral malleolus of ankle
- Patella at knee
Cams
- Characteristics of first class lever and simple pulley.
- Typically implemented with lever, pulley, gear and chain mechanisms.
- Examples
- Used in weight training machines to vary resistance throughout movement
- in attempt to match natural strength curve (e.g.: Nautilus, Cybex, etc.)
- or develop strength curve throughout a targeted portion of the movement
- eg: Strive Smart Strength Equipment
- See image of adjustable variable cam.
- Used in weight training machines to vary resistance throughout movement
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Incline Plane
- Examples
- Pushing or pulling a loaded wagon up a slope.
- Cycling up the side of a hill.
- Exercise Examples
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Gears, belts, and chains
- Characteristics
- Can change direction, speed, or force
- Speed of rotation inversely affects force transmitted
- Bigger wheel rotates more slowly but with more force at the axle
- gears are comparable to first class lever
- belts and chains are similar to simple pulley
- Types of Gears
- Spur:
- two gears on same plane (parallel axles)
- Rack and pinion:
- one wheel and one rack (flat toothed bar)
- converts rotary motion into linear motion or vice versa
- Bevel
- AKA: pinion and crown or pinion and ring gears
- two wheels intermesh at an angle changing the direction of rotation (the axles are not parallel)
- Worm
- one wheel gear (a pinion) and one shaft with surrounding screw thread
- Spur:
- Belts and chains
- work like spur gears, but do not change direction of motion
- Examples
- Some weight training equipments
- Cycling
- Current speed (mph) = (gear inches x 3.14) x (rpm x 60) / 63.36
- Also See Cycling Gear Chart Calculator