L25 - Energy

Subdecks (1)

Cards (28)

  • Defining Energy:
    • Definition: the capacity or ability to do work
    • Many forms:
    • Thermal, chemical, nuclear, electromagnetic & mechanical
    • Mechanical Energy is measured in Joules (J)
    • Produced from muscle & what sporting equipment is designed for
    • To absorb or transfer energy
  • Mechanical Energy Forms:
    • Kinetic energy - related to a body’s motion
    • Linear or rotational
    • Linear kinetic energy is calculated as 1/2 the body’s mass (m) multiplied by the square of its velocity (v)
    • Ek = (½ * m) * v^2
    • Velocity more important as it is squared
    • Rotational kinetic energy is calculated using the mass moment of inertia (I) of the body in motion & its angular velocity (ω)
    • E<k = ½ * I * ω^2
  • Mechanical Energy Forms:
    • Potential energy - energy of position or deformation
    • 2 forms
    1. Gravitational potential energy, which is 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
    2. Deformation energy or strain energy, which is the energy stored in a body by virtue of its deformation
  • Mechanical Energy Forms:
    1. Gravitational potential energy, which is 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
    • Ep = m * g * h
    • Height = CoM from the ground
  • Mechanical Energy Forms:
    • 2. Deformation energy or strain energy, which is the energy stored in a body by virtue of its deformation
    • Mathematically describing the amount of energy will depend upon the material properties of the deformable body
    • Ie no single equation can describe the deformation of all bodies
    • More important for sport performance & equipment
    • Deforms to absorb energy, to give energy back to system
  • Mechanical Energy Forms - Deformation:
    • Es = ½ * k * Δ x^2
    • k = constant; each material have a strain factor/constant
    • How much resistance to deformation
    • Protective equipment look at k value (resistance to deform), how much energy store in equipment (so not transferred to body)
    • Guidelines for k for most sports like sprinting & pole vaulting
    • Change in Δx^2 = the distance
    • eg a string in a bow, how much energy can store in bow
    • pole vault, how much reform & how much returned
    • How much bend/flex in hockey stick (more weight, more flex), bending stick allows to put more energy into hitting the puck
  • Assumptions: Mechanical Energy:
    • Total mechanical energy (TME) is the sum of the linear kinetic, angular kinetic, & positional potential energy + strain energy
    • Sum of all forms of energy
    • TME = Ek + E<k + Ep = ( ½ m v^2 ) + ( ½ I ω^2 ) + (m g h)
    • TME = scalar quantity
    • Ignore strain as assume bones are rigid & changing
    • Is a bad assumption as bones do deform (all the time)
    • Mechanical strain is what makes them strong
    • Equations is hard to know how much deformation is taking place at bone so is ignored
    • Although… We often assume the body is rigid or non deformable
  • Principles: Conservation of Energy:
    • Gravity is a conservative Force
    • If primary external force (in the air/falling)
    • When gravity is the only acting external force a body’s mechanical energy remains constant
    • (PE + KE) = C
    • PE = potential energy; KE = Kinetic energy
    • C = conserved/constant
    • Won’t change when in air, but the potential & kinetic energy trade off
    • Peak = 0 velocity/kinetic energy, all potential energy
    • As get further from peak = potential energy decrease, kinetic energy increase
  • Principles: Conservation of Energy:
    • What are some of the key points in this statement?
    • Energy is neither created or destroyed (thermal dynamics)
    • Can’t generate/create energy that way
    • Lose in one gain in the other (trade off bw/ potential & kinetic energy)
    • Have to be in the air, no other forces acting on you (energy conserved in air)
  • Principles: Conservation of Energy (ball example):
    • Total Energy = Ek + Ep
    1. Max velocity = max kinetic energy
    2. As the ball ascend the potential energy increases while kinetic energy decreases bc/ gravity is slowing the flight
    3. At the peak of trajectory the v^2 of the ball = 0 thus no kinetic energy. h = maximum = max potential energy
    4. Downward flight the reverse change in energy occurs
  • Principles: Conservation of Energy (ball example):
    • Experiment: throwing ball look at transfer of energy
    • Moment released greatest velocity lowest potential; as move up velocity decreased and potential increased
    • Potential highest at peak height
    • When closed system, no other external forces acting
  • Principles: Conservation of Energy:
    • Trampolining/gymnastics
    • Energy from mat, same idea as above
  • Law of Conservation of Mechanical Energy:
    • If the resultant force acting on a body is a conservative force then the body’s 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)