biomechanics final

mechanical work

something you “do”

product of force/torquw applied to the object and the displacement caused by the force

produced when force causes the object to move or deform

positive work

force and displacement are in the same direction

negative work

the force and object’s displacement are in opposite directions

displacement is 0

no work is done (like planking/isometric)

concentric contraction

positive work

eccentric contraction

negative work

mechanical energy

the energy the objects possess due to motion or position in space

something the object “has”

scalar (always positive)

two forms of mechanical energy

kinetic

potential

kinetic energy

energy possessed by moving object

“energy of motion”

determined by mass and velocity

potential energy

energy stored in an object due to its height or deformation

gravitational or strain

gravitational potential energy

potential energy and object possesses due to its height

determined by mass and height

strain

potential energy an object possesses due to deformation

• energy is stored in object when

  • obejct is compressed

    • object is stretched

energy is neither created nor destroyed

it’s converted to another form

like a car engine

law of conservation of mechanical energy

when gravity is the only external force acting on the object, the total mechanical energy remains constantth

the mechanical energy of an object changes only when…

the energy is being transferred to or from another object

diver standing on cliff

potential energy

diver dives

turns into kinetic energy

as the diver falls, his COM _____. as a result, the gravitaional potential energy of the body _____. downward velocity will _____. as a result, kinetic energy will ______. total energy will _____.

DECREASES. DECREASES. DECREASE. INCREASE. STAYS THE SAME

work-energy relationship

work produced on an object is equal to the change in mecanical energy of the object

when an object produces mechanical work on another object, energy is being transferred

power

rate at which the mechanical work is produced

represtents rate of energy transfer

the more mechanical work produced over shorter time…

the higher the power produced

high pwer=

high force at high velocity

strength training effect on power

increases power production capacity (improves muscle strength)

• training specific to improving force production at high velocity results in better results

power is + when

work is +

muscle in contracting concentrically

power is - when

work is - and muscle is contracting eccentrically

fluid

anything that can flow and change shape quickly

fluid force

force exerted on the object by the fluid as the object is placed in fluid or is moving relative to the fluid

buoyant force

upward force that acts on any objects that are placed in fluid

dynamid fluid force

force that acts on obejct when there is a relative motion between the object and the fluid

• object is travelling thru fluid and/or

  • fluid is moving around the object (wind blowign around u)

buoyant force magnitude

buoyant force magnitude is equal to the weight of the fluid displaced by the object

greater the volume and higher the density of the fluid displaced by the object, the greater the weight of the fluid displaced

net force acting on the object in vertical direction is…

the sum of the weight of the object and the buoyant force

object floats when

weight of the object is equal to buoyant force

object sinks when

weight of the object is greater than the buoyant force

boundary layer

thin layer of fluid adjacent to object’s surface

wit

within the boundary layer

fluid closest to object moves with the object

fluid farthest from object moves with fluid around it

difference in velocity between object and fluid around it creates friction within boundary layer

laminar flow

smooth and regular flow of particles

initially contours the object, but eventually moves away fromit

smoother object= longer it follows its contour

turbulent flow

area of low pressure

can develop on surface boundary layer or behind the object

wake

turbulent flow that develops behind the object

earlier the laminar flow separates, the greater the turbulent flow and bigger the wake

how is dynamic fluid produced?

fluid particles produce force against the object

dynamic fluid force is collective force produced by the fluid particles around the object

two components of dynamic fluid force

drag force

lift force

drag force

component of dynamic fluid force

acts parallel to the direction of fluid that passes the object

lift force

component of dynamic fluid force

acts perpendicularly to the flow of fluid that passes the object

drag force tends to ___ object’s motion

resist

decreasing drag is important in speed and time sports!

the lift force will ____ or ___ the object’s path of motion

turn or bend.

the lift force sometimes lifts the object up, but not always

drag force is produced by

surface drag

pressure drag

surface drag

friction between object and fluid

created in boundary layer due tto difference in velocity

pressure drag

difference in pressure between front and back sides of object

front of object: collision between object and fluid = area of high pressure

behind object: wake creates area of low pressure

greater the pressure difference,

greater the pressure drag

what factors affect drag force?

relative velocity between fluid and object

characteristics of object (size, frontal shape, smoothness)

characteristics of fluid (density & viscosity)

relative velocity

object’s velocity relative to fluid velocity

subtract ur velocity minus velocity of fluid

high drag coefficient

more resistance and more drag experienced by the person/object

low drag coefficient

less resistance and less drag experienced by the person/object

how is the M5 low racer different than riding a regular upright bike?

m5 has a smaller projected front area and smaller draeg coefficient. therefore, it experiences less drag forces and the rider doesn’t have to work as hard to overcome the wind

two ways in which lift force is created

angle of attack

magnus effect

angle of attack

angle of object relative to direction of motion. greater angle, greater lift force.

greater lift force= longer flight time (BAD)

greater angle= greater drag force (due to increased projected front area

greater drag force= greater resistance moving forward (BAD)

magnus effect

deflection in the path of the spinning object caused by the lift force created by the object’s spin.

causes trajectory of an object traveling through air to “bend”

ex curve balls in baseball, slicing and hooking in golf

density

mass per volume

higher density of fluid= grater pressure and surface drag

HIGHER ALTITUDE AND TEMPERATURE RESULTS IN LOWER FLUID DENSITY

LOWER DENSITY IS EASIER TO FLOW THRU

viscosity

thickness

measure of resistance to flow

higher the viscosity, greater the pressure drag and surface drag

higher temperatures lower viscosity

drag coefficeint

value that quantifies the resistance of an object in the fluid due to surface and pressure drag

measure of aerodynamics/hydrodynamics

lower drag coef= lower resistance (more aerodynamic)

drafting (trailing close to another rider)

used to decrease drag force acting on cycliss

decreases drag force of back rider by decreasing relative velocity between rider and fluid

decreases drag force on front rider by decreasing wake

when fluid is turned up by object, the lift force will push the object

up

when fluid is turned down, the lift forward will push the object

down

when the fluid is turned right by the object, the lift force will push the object

left

when the fluid is turned left by the object, the lift force will push the object

right

magnus effect on ball increases as

as the linear and angular velocity (spin rate ) increases

when the angle of attack is very small…

decreases the drag force but also decreases the lift force, leading to less flight time

when the anfle of attack is very large..

increases lift force which increases flight time, but increases drag force and resistance

optimal angle of attack

angle at which effects of lift fprce and drag force on object is optimized

magnus effect on downward ball spin

results in upward lift force

open club face angle

club glides along left side of ball, resulting in ball curving to the right

closed club face angle

club glides along right side of the ball, resulting in ball curving to the left

how mass of object affects effects of fluid force on projectile motion

smaller mass= stronger influence of fluid force

how dynamic fluid force acting on object affects effects of fluid force on projectile motion

greater fluid force= stronger influence of fluid force