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
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
Deformation energy or strain energy, which is the energy stored in a body by virtue of its deformation
Mechanical Energy Forms:
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:
Totalmechanicalenergy (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
Max velocity = max kinetic energy
As the ball ascend the potential energy increases while kinetic energy decreases bc/ gravity is slowing the flight
At the peak of trajectory the v^2 of the ball = 0 thus no kinetic energy. h = maximum = max potential energy
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)