Basic BiomechanicsBasic Biomechanics• Mechanics-study of forces and

motions produced by their action.• Biomechanics-apply that to the

structure and function of the human body.

Basic BiomechanicsBasic Biomechanics• Statics deal with factors associated

with nonmoving.• Dynamics deal with moving systems

– Kinetics are the forces causing the motion

– Kinematics are time, space and mass of the moving system.

Basic BiomechanicsBasic Biomechanics• Kinematics-

– Osteokinematics bones moving in space in regard to joint surface (flexion)

– Arthrokinematics are the manner in which joint surfaces move in relation to each other.(concave)

Basic BiomechanicsBasic Biomechanics• Vector- mechanical quantity having

both magnitude and direction– Force is vector quantity-push or pull

action– Force has direction and magnitude– You throw a ball with direction and

speed

Basic BiomechanicsBasic Biomechanics• Scalar- mechanical quantity that has

only magnitude(strength of force). – Common scalar terms=Length, area,

volume, mass• Mass is the amount of matter a body

contains.• Inertia is change in motion in either

speed or direction.

Basic BiomechanicsBasic Biomechanics• Law of Inertia- an object at rest tends

to stay at rest, and an object in motion tends to stay in motion.

Basic BiomechanicsBasic Biomechanics• Think about what happens with your

head in a car. It is not in motion, so when acceleration/deceleration happen your neck is not always happy.

Basic BiomechanicsBasic Biomechanics• Law of Acceleration-the amount of

acceleration depends on the strength of the force applied to an object.

Basic BiomechanicsBasic Biomechanics• Acceleration is inversely proportional

to the mass of an object.– If you roll a soccer ball , then a bowling

ball, with the same force, the heavier object will not travel as far.

Basic BiomechanicsBasic Biomechanics• Law of action-reaction- every action

there is an equal and opposite reaction.– Strength of reaction is equal to strength

of action, just in the opposite direction.– Harder you

jump harder you rebound.

Basic BiomechanicsBasic Biomechanics• Go outside and create a

demonstration of one of the laws of physics for us all to understand.

• In a simple paper write up what you have done and how it demo the law you chose.

• You have 30 minutes to complete this task and paper.

Basic BiomechanicsBasic Biomechanics• Force -a vector describes both

magnitude and direction; push or pull; one object must act on another object

For example a person pulling a box with a rope. The rope tension is the magnitude, the pull on rope is the direction.

Basic BiomechanicsBasic Biomechanics• Force -a vector describes both

magnitude and direction– Linear force- 2 forces act on the same

line in the same direction or opposite direction.

or

Basic BiomechanicsBasic Biomechanics• Parallel Forces-

– In the same plane and in the same or opposite directions.

Basic BiomechanicsBasic Biomechanics• Concurrent Forces- two or more

forces act from the same common point but pull in different directions. Resultant force will move toward

stronger force.

Basic BiomechanicsBasic Biomechanics• Concurrent Forces- two or more

forces act from the same common point but pull in

different directions

Basic BiomechanicsBasic Biomechanics• Force Couple- two forces act in an

equal but opposite direction resulting in a turning effect.

TorqueTorque• Torque is the amount of force

needed by a muscle contraction to cause rotary joint motion.

• This is most effective at » 90 degrees» Read Torque(pg 97)» Fig 8-9, 8-10, 8-11

TorqueTorque– Angle of Pull: angle between muscle insertion and bone on which it inserts.

• Components of Force – Angular Force: force of a muscle contributing to bone's movement around a joint axis;

greatest when muscles angle of pull is perpendicular to bone (i.e. 90 degrees). – Stabilizing force: degree of parallel forces generated on the lever (bone and joint) when the

muscles angle of pull is less than 90 degrees. – Dislocating force: degree of parallel forces generated on the lever (bone and joint) when the

muscle's angle of pull is greater than 90 degrees. force directed away from the joint (distal)

Basic BiomechanicsBasic Biomechanics• State of equilibrium- when all torques

acting on an object are even.• Center of gravity- COG-balance point

of an object at which torque on all sides are equal.

• In an adult the center of gravity is just anteior to s2

Basic BiomechanicsBasic Biomechanics• Base of support is that part of the

body that is in contact with the supporting surface. (BOS)

• Line of gravity is the imaginary vertical line that passes through the COG to center of earth. (LOG)

• Draw this in your notes pg 78

Basic BiomechanicsBasic Biomechanics• Equilibriums

– Sable- to disturb you would have to raise COG

– Unstable- only slight force needed to disturb

– Neutral- COG is not raise or lowered to disturb.

– Lower COG is more stable.

Basic BiomechanicsBasic Biomechanics• The closer COG is to center of BOS

the more stable you will be

Basic BiomechanicsBasic Biomechanics• Lets try it together. • Stand up and stand on both legs,

then balance on one standing straight up.

• Then lean to the side you are standing on. What changes.

• Go do questions 7&8 in text pg 90discuss

Basic BiomechanicsBasic Biomechanics• List some ways to increase stability

– Wider base of support– Greater mass (which will decrease

speed)– Increase friction (carpet vs ice)– Focus on stationary

Basic BiomechanicsBasic Biomechanics• Simple Machines

– 4 types of Machines• Lever• Wheel and Axle• Inclined plane• The pulley

Basic BiomechanicsBasic Biomechanics• Lever is a rigid bar that can rotate

about a fixed point when a force is applied to overcome resistance.

Basic BiomechanicsBasic Biomechanics• A-Axis is the fixed point around which

the lever rotates.• F-Force causes the lever to move.

(muscle in the body)• R-Resistance that must be overcome

for motion to occur. ( can be gravity or the weight to move.)

Basic BiomechanicsBasic BiomechanicsForce Arm is distance between force

and axisResistance arm is distance from axis to

resistance.

A F R

Basic BiomechanicsBasic Biomechanics• First-class lever FAR

– Axis is located between the force and the resistance.

– Balance

F

R

A

Basic BiomechanicsBasic Biomechanics• Second Class Lever ARF

– Has the axis at one end, the resistance in the middle, and force at the other end.

– power

AR F

Basic BiomechanicsBasic Biomechanics• Third class Leaver

– Has the axis at one end with the force in the middle and resistance at the opposite end.

– ROM

A FR

Basic BiomechanicsBasic Biomechanics• The body has more 3rd class levers

because the body favors the advantage of ROM.

• Levers can change class depending on where the resistance is, if there is resistance added vs just gravity. Or if the direction gravity comes from changes. Pg 83-84

Basic BiomechanicsBasic Biomechanics• Mechanical Advantage- ratio

between the force arm and resistance arm.

MA=FA RALess force is needed when mechanical advantage is greater.

Page 85 force arm on leg

Basic BiomechanicsBasic Biomechanics• Pulley is a grooved wheel that turns

on axle with rope or cable. – It allows for change of direction of force

or to change the magnitude of a force.

Basic BiomechanicsBasic Biomechanics• Fixed pulley is one attached to a

beam. It acts like a fist class lever, it is used to change directions.

• Medical malleolusActs as a pulley for the Tendon of peroneuslongus

Basic BiomechanicsBasic Biomechanics• Movable pulley has one end of the

rope attached to a beam then the rope runs through the pulley to the other end where the force is applied.

• What is gained in force is lost in distance.

Basic BiomechanicsBasic Biomechanics• Wheel and Axle- a lever in disguise.

– Wheel with a crank attached. It helps increase the force exerted.

– Large radius requires less force.

Basic BiomechanicsBasic Biomechanics• Incline Plane is a flat surface that

slants.– It creates more distance with less effort

Simple MachinesSimple Machines• Basic rule of simple machines: what

is gained in force is lost in distance.• Lever lab