Lecture 30 - Work Energy Theorem Flashcards
what is energy
the capacity or ability to do work
what are examples of forms of energy
thermal, chemical, nuclear, electromagnetic and mechanical
mechanical energy is measured in
Jules (J)
kinetic energy is related to
a body’s motion (linear or rotational)
linear energy is calculated as
one half of the body’s (m) multiplied by the square of its velocity (v)
what is the equation of linear kinetic energy
EK = 1/2 m v^2
rotational kinetic energy is calculated using
the mass moment of inertia (I) of the body in motion and its angular velocity (w)
what is the equation of rotational kinetic energy
E<K = 1/2 I w^2
what is potential energy
energy of position or deformation
what are the two forms of potential energy
gravitational potential energy
deformation energy / strain energy
what is gravitational potential energy
the potential of a body to do work as a function of height (h) with respect to a reference surface, where g is gravitational acceleration
what is deformation energy or strain energy
energy stored in a body by virtue of its deformation
mathematically describing deformation energy will depend upon
the amount of energy will depend upon the material properties of the deformable body
i.e no single equation can describe the deformation of all bodies
what is the equation for gravitational potential energy
Ep = m g h
what equation is for deformation energy
Es = 1/2 k change in x^2
what is total mechanical energy (TME)
the sum of the linear kinetic, angular kinetic, and positional potential energy
total mechanical energy is a
scalar
gravity is a what force
conservative force
when gravity is the only acting external force, a body’s mechanical energy is what
remains constant
(PE + KE) = C
at the gravitational potential energy and kinetic energy when the ball is at the apex
gravitational energy is at max
kinetic energy is 0
at the gravitational potential energy and kinetic energy when the ball hits the ground
gravitational potential energy is 0
kinetic energy is max
in terms of the conservation of energy, when something has max velocity = what is said about kinetic energy
max velocity = max kinetic energy
as the ball ascends into the air what happens to energy
gravitational energy increases and kinetic energy decreases because gravity is slowing the flight
if the resultant force acting on a body is a conservative force then the
bodys total mechanical energy will be conserved
resultant force will be conservative if all
external forces are conservative
a force is conservative if
it does no work around a closed path (motion cycle)
is walking more efficient than running
it depends, walking more efficient than running at certain speeds
what happens to force the faster you run
the faster you run, the more force you need to apply
what is probably not a reason that we transition from walking to running
metabolic energy expenditure
what is probably reasons why we transition from walking to running
- peak ground reaction force ?
- velocity of ankle motion ?
- the length of your leg ?
what happens to the amount of force we develop as we increase speed when walking
when we get to a certain rate of force development that we can no longer maintain that amount of hip rotation we begin to run
walking is restricted by hip rotation due to dual stance
as our velocity increases the power consumption will increase, what is this limited by
limited by our leg length
what is the power and speed curve like between running and walking and why
walking has an exponential curve and running is linear, as we are not limited by leg length in running
why is there a transition from walking to running in terms of power and speed
there is a point where to continue to provide enough mechanical energy to maintain the pendulum it becomes more costly than the spring
