Work, Energy, Power Flashcards
What is a definition of work?
The energy transferred to a body by a force
What two requirements are there for work to be done?
- A force needs to act on a body
- Movement needs to occur
What is the equation for work?
What are its units?
Force x distance
Nm = Joules (J)
What is power?
What is the equation to calculate power?
What are the units of power?
The rate at which work is done
Work / time
J.s-1 = Watt (W)
What is the formula for kinetic energy?
m.v2/2
How is the formula for kinetic energy derived?
= F.d
=m.a.d
=m.((v2-v1)/t).(v1+v2).t/2)
(where v1 -= 0)
=m.v2^2/2
What is the equation linking power to force and how is it derived?
Power = work/time
= F.d/t
=F.v
(either instantaneous or average)
What is the formula for angular power?
T.w
What is the sign convention for muscular power?
+ve - working concentrically
-ve - working eccentrically
Definition of energy (from a mechanical perspective)?
The capacity of a body to do work
What are the 3 types of energy in mechanics?
- Kinetic energy
- Potential energy
- Elastic energy
Formula for rotational kinetic energy?
I(w^2)/2
Derivation of rotational kinetic energy formula?
= kinetic energy of sum of all individual parts (molecules of body)
= sum (mass(i).(v(i)^2)/2
= sum (mass(i)(w(i)^2)(r(i)^2)/2
= (w^2) sum (mass(i).(r(i)^2))/2
= (w^2).I/2
Formula for potential energy?
m.g.h
Formula for elastic energy?
stiffness.(change in length^2)/2
= k.(delta l ^ 2)/2
Where k = spring constant
Derivation of formula for elastic energy?
Compressive force F = k . distance compressed (l)
Where k = spring constant
Energy = work done = integration of the force distance curve
= k . l^2 / 2
What is the law of conservation of energy?
In a closed system energy cannot be created or destroyed
What is a closed system?
A system which is isolated from its surroundings and does not experience any forces external to it
What concept and formula do you use to determine the velocity of block which has slid h metres measured vertically down a slope of frictionless ice of varying gradient?
Law of conservation of energy
m.g.h = m.v^2/2
What is the relationship between work done and energy
Change in energy = work done
Explain what constitutes positive and negative work regarding muscular force.
What is the application of this with regard to a dumbbell curl?
Positive work = force applied in same direction as movement takes place (muscle working concentrically)
e.g. upwards movement of dumbbell curl
Negative work = force applied in opposite direction as movement takes place (muscle working concentrically)
e.g. downwards movement of dumbbell curl
What is the definition of internal vs external work?
Give examples
Internal work - work which results from the motion of body segments (e.g. dumbbell curl)
External work - work which is done on the whole body (e.g. going up/down stairs)
