Week 4 - Work, Energy & Power

work (U)

another way of describing the effect of a force

• is done on an object when a force causes a change in position

• the product of average force and displacement

work equation

U = Fd

positive work (concentric)

done by a force acting on an object if the object is displaced in the same direction as the force

negative work (eccentric)

done by a force acting on an object when the object is displaced in the direction opposite to the force acting on it

Example of negative work in the gait cycle?

early stance phase (loading response)

energy

the capacity to do work

kinetic energy (KE)

energy resulting from motion

linear KE equation

KE = 0.5mv²

potential energy (PE)

capacity to do work because of position or form

linear PE equation

PE = mgh

conservation of mechanical energy

when gravity is the only external force, mechanical energy remains constant

conservation of mechanical energy equation

TE = KE + PE

What is the path of the CoM during walking gait?

inverted pendulum

Where is the PE the greatest?

functional location of CoM

Where is the KE the greatest?

midstance/ when potential energy is lowest

work-energy relationship

when a force, excluding gravity, performs work on an object, there is a change in total mechanical energy

(work is = to the change in total energy that it produces on an object)

where is PE greatest in running?

during float phase

work-energy relationship equation

U = ΔKE + ΔPE

law of conservation of energy

PE is OPPOSITE KE in magnitude

if vGRF is high then KE ____ and PE _____

high, low

power

the rate at which work is performed

power equation

power = F*d/Δt

power is an indicator of the ____ of the task

intensity

What are the components of human power production?

strength (force producing ability) and speed (velocity) of muscle contraction

Force-velocity relationship

as speed increases, maximal force production capability decreases