Lecture 29 - Work and Power Flashcards
we must apply a force to
move and object or mass
when we use force to move a mass this is
called work
equation for work
W = F x s (Jules)
units are Nm but usually represented as Joules (J)
what are the 3 principles of work
- a force can only do work is it causes displacement
- a force can do work only for the duration of the displacement
- only the force acting in the direction of displacement can do work
can work be negative
yes work can be positive of negative
if there is no movement …..
there is no work, you can not measure work for an isometric contraction
what is positive work
when object moves in direction of applied force
- force vector is in the same direction as the displacement vector
what is negative work
when object moves opposed direction of applied force
- force vector is in opposite direction of displacement vector
negative work occurs under what type of contraction
eccentric contraction
if two people move the same mass through the same distance, what is said about work
the amount of work they do is the same
what is power
measures the rate at which we do work
equation of power
P = W/t (watts)
power is limited by the rate of what
atp transition
limitation of power production in humans
connecting cross linkages and activating muscle fibres takes time, as load increases so does the number of active fibres
maximum power is generated at approx
one third of maximum shortening velocity
because power is derived from the work equation, the same rules apply, what are they
- no movement = no work = no power
- measured in the direction of movement (velocity vector in rotation)
- power may be positive or negative (see this as producing or absorbing)
- time dependent waveform
what is instantaneous power
highest power value achieved during the observed movement
what is average power
calculated for average force and average velocity for a given movement
the power produced by joints can be determined by the product of
the product of the net torque and the joint angular velocity
we can derive joint power time curve by
multiplying our angular velocity and angular acceleration curves together
when both the angular velocity and angular acceleration have the same sign (either positive or negative) power will be ….
power will be positive
power production is
when power is positive (so angular velocity and acceleration have the same sign)
when angular velocity and angular acceleration have different signs (one positive and one negative), power will be
power will be negative
what is power absorption
when power is negative, think of it as a breaking mechanism
