Simple body machines

Simple body machines 1- Levers. 2- Pullys. 3- Wheel and axle. Musculoskeletel system arrangement provides for 3 types of machines in producing movement: 1- Levers. 2- Pullys. 3- Wheel and axle.

Pulley is a simple machine, that performs a mechanical job. Definition Pulley is a simple machine, that performs a mechanical job. It consists of a grooved wheel and a cord or a rope running over it.

Types of pulleys 1. Fixed pulley 2. Mobile pulley 3. Mixed pulley

Fixed pulley It is the only example of pulley in human body A fixed pulley changes the direction of a force. Mechanical advantage = 1

mobile pulley It is used in exercises. The mechanical advantage of a mobile pulley is equal to the number of ropes that support the mobile pulley.

Mixed pulley It is used in exercises. The combination between fixed and mobile pulleys. Mixed pulleys acts to increase mechanical advantage. Each additional rope increases mechanical advantage by 1.

Functions of pulleys Change direction of force Balance of force Modify the effect of a force Magnify the force via increasing the MA

1. Wheel: Represented by bony component which can be Human equivalents 1. Wheel: Represented by bony component which can be External bone: as patella Bony prominence: as condyles, trochanters, tuberosities 2. Rope or Cord: is represented by tendon, muscle, musculotendinous junction.

Patella as a pulley Patella acts as an external pulley for the tendon of quadriceps muscle tendon

Patella as a pulley

Patella has the following functions Move the muscle away Increase the moment arm Increase the quadriceps torque Patella has the following functions Increase the angle of pull Increase the rotatory component Increase the efficiency of quadriceps muscle Improve the mechanical advantage

Lateral malleolus bone as a pulley lateral malleolus acts as a pulley around which tendon of peroneus longus runs. As peroneus longus contracts, it pulls toward it belly (toward the knee). Using the lateral malleolus as a pulley, force is transmitted to plantar aspect of foot resulting in eversion/plantarflexion.

Wheel and axle Center of the wheel & the axle both correspond to the fulcrum Both the radius of the wheel & the radius of the axle correspond to the force arms

Wheel and axle When either the wheel or axle turn, the other must turn as well Both complete one turn at the same time

Wheel and axle If the wheel radius is greater than the radius of the axle, then, due to the longer force arm, the wheel has a mechanical advantage over the axle a relatively smaller force may be applied to the wheel to move a relatively greater resistance applied to the axle if the radius of the wheel is 3 times the radius of the axle, then the wheel has a 3 to 1 mechanical advantage over the axle

Wheel and axle calculate mechanical advantage of a wheel & axle by considering the radius of the wheel over the axle Mechanical radius of the wheel advantage = radius of the axle Mechanical 3 advantage = 1

Wheel and axle If application of force is reversed and applied to the axle, then the mechanical advantage results from the wheel turning a greater distance & speed if the radius of the wheel is 3 times the radius of the axle, then outside of the wheel will turn at a speed 3 times that of the axle. the distance that the outside of the wheel turns will be 3 times that of the outside of the axle.

Wheel and axle Mechanical radius of the axle Calculate the mechanical advantage for this example by considering the radius of the wheel over the axle Mechanical radius of the axle advantage = radius of the wheel Mechanical 1 advantage = 3

Wheel and axle Used primarily to enhance range of motion & speed of movement in the musculoskeletal system function essentially as a form of a lever Ex. resulting in greater range of motion & speed is with upper extremity in internal rotators attaching to humerus: Humerus acts as the axle. Hand & wrist are located at the outside of the wheel when elbow is flexed 90 degrees. With minimal humerus rotation, the hand & wrist travel a great distance. Allows us significantly increase the speed at which we can throw objects.

The 6 Simple Machines Pulley Lever Wheel and Axle Inclined Plane Screw Wedge

Inclined Planes An inclined plane is a flat surface that is higher on one end. Inclined planes make the work of moving things easier.

Inclined Planes Work input: is the amount of work on a machine. Input force x input distance Work output: is the amount of work done by a machine. Output force x output distance Work out = Work in F out x D out = F in x D in 10 N x 3 m = 2 N x 15 m D in 15 m D out 3 m F in F out 10 N

length of the slope height of the inclined plane Mechanical Advantage (MA) Definition It is the way to measure the efficiency of this machine that means the ability of the machine to magnify force or to increase the output in relation to the input. Mechanical advantage of the inclined plane = length of the slope height of the inclined plane

Inclined Plane Mechanical Advantage The mechanical advantage of an inclined plane is equal to the length of the slope divided by the height of the inclined plane. While the inclined plane produces a mechanical advantage, it does so by increasing the distance through which the force must move.

Inclined Plane Mechanical Advantage Sloping surface used to lift heavy loads with less effort

A screw is an inclined plane wound around a central cylinder

Wedges Two inclined planes joined back to back. Wedges are used to split things.

Wedges Converts motion in one direction into a splitting motion that acts at right angles to the blade.

Wedges Wedges change the direction of an applied force. When force is applied downward on a wedge, it distributes the force outward in two directions, separating a material.

Wedges Mechanical Advantage The mechanical advantage of a wedge can be found by dividing the length of either slope (S) by the thickness (T) of the big end. As with the inclined plane, the mechanical advantage gained by using a wedge requires a corresponding increase in distance.

Compound Machine Bowflex: Pulley lifts the weight, the seat is an inclined plane, and the lever is what you pull to adjust the seat.

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