Lecture 29 - Work and Power

Question 1

we must apply a force to

Answer 1

move and object or mass

Question 2

when we use force to move a mass this is

Answer 2

called work

Question 3

equation for work

Answer 3

W = F x s (Jules)

units are Nm but usually represented as Joules (J)

Question 4

what are the 3 principles of work

Answer 4

1. a force can only do work is it causes displacement
2. a force can do work only for the duration of the displacement
3. only the force acting in the direction of displacement can do work

Question 5

can work be negative

Answer 5

yes work can be positive of negative

Question 6

if there is no movement …..

Answer 6

there is no work, you can not measure work for an isometric contraction

Question 7

what is positive work

Answer 7

when object moves in direction of applied force
- force vector is in the same direction as the displacement vector

Question 8

what is negative work

Answer 8

when object moves opposed direction of applied force
- force vector is in opposite direction of displacement vector

Question 9

negative work occurs under what type of contraction

Answer 9

eccentric contraction

Question 10

if two people move the same mass through the same distance, what is said about work

Answer 10

the amount of work they do is the same

Question 11

what is power

Answer 11

measures the rate at which we do work

Question 12

equation of power

Answer 12

P = W/t (watts)

Question 13

power is limited by the rate of what

Answer 13

atp transition

Question 14

limitation of power production in humans

Answer 14

connecting cross linkages and activating muscle fibres takes time, as load increases so does the number of active fibres

Question 15

maximum power is generated at approx

Answer 15

one third of maximum shortening velocity

Question 16

because power is derived from the work equation, the same rules apply, what are they

Answer 16

• 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

Question 17

what is instantaneous power

Answer 17

highest power value achieved during the observed movement

Question 18

what is average power

Answer 18

calculated for average force and average velocity for a given movement

Question 19

the power produced by joints can be determined by the product of

Answer 19

the product of the net torque and the joint angular velocity

Question 20

we can derive joint power time curve by

Answer 20

multiplying our angular velocity and angular acceleration curves together

Question 21

when both the angular velocity and angular acceleration have the same sign (either positive or negative) power will be ….

Answer 21

power will be positive

Question 22

power production is

Answer 22

when power is positive (so angular velocity and acceleration have the same sign)

Question 23

when angular velocity and angular acceleration have different signs (one positive and one negative), power will be

Answer 23

power will be negative

Question 24

what is power absorption

Answer 24

when power is negative, think of it as a breaking mechanism

Question 25

what is the equation of rotational power

Answer 25

power = Tw