Week 11 - Defining Energy Flashcards
Define Mechanical energy and itβs two types
The energy that is possessed by an object due to its motion or due to its position
Kinetic Energy (KE) - energy due to motion
Potential Energy (PE) - energy stored due to position
Kinetic Energy equation
KE = 1/2 * mass (m) * velocity2
What is the kinetic energy of a tennis ball with the mass of 60 g and the velocity of 108 km/h (30 m/s)?
πΎπΈ = 1/2*π*π£ 2
KE = 1/2*0.06*30squared
KE = 27 J
How much energy must be absorbed by the wicket keeper when a 300 g ball travelling at 100 km/hr (27.78 m/s) is caught?
πΎπΈ = 1/2 β π β π£ 2
πΎπΈ = 1/2 β π β π£ 2
KE = 1/2*0.3*27.78squared
KE = 115.76 J
Absorbed - so this is negative energy
Potential energy and itβs two types
Stored energy based on an objects position
Gravitational Potential Energy - Energy due to an objectβs position relative to the earth
Strain energy - Energy due to the deformation of an object
Define Gravitational potential energy and equation
Related to the objectβs weight and its elevation or height above the ground or some reference point
Gravitational potential energy (PE)
= mass (m) * acceleration due to gravity (g) * height (h)
PE = mgh
What is the potential energy of an 80 kg diver on a 10 m platform?
ππΈ = ππβ
ππΈ = ππβ
80 * 9.81 * 10
PE = 7848 J
Define Strain energy and the equation
Special form of potential energy, also called elastic energy. e.g. pole volters pole
Strain Energy (SE) = 1/2 spring constant * distance material is deformed2
ππΈ = 1/2*π*π₯2
Spring constant (k)
varies depending on the stiffness of the material
Easy to deform = small k value
Hard to deform = large k value
Strain/Elastic energy in the human body
Springs in the human body - Most tissue types are βelasticβ
Tendons and ligaments = effective springs - Stretch ~8% without breaking and return ~93% of the strain energy they store
During running - Tendons and ligaments return ~3,000 J/kg
- Muscle returns ~3 J/kg the rest of the absorbed kinetic energy is converted to heat energy
