lesson 8

Energy

SI unit: Joule (J)

scalar

law of conservation of energy

mechanical energy = potential energy + kinetic energy

Total Energy in the beginning = Total Energy in the end
PE1 + KE1 = PE2 + KE2

Kinetic energy (Linear)

energy of a moving object because of its motion

KE = 1/2 mv^2
m = mass [kg]
v = velocity [m/s]
KE = kinetic energy [J]

potential energy

potential energy is stored in the object

Gravitational potential energy

GPE = mgh
m = mass[kg]
g = gravitational acceleration [m/s^2] = 9.81m/s^2
h = height [m]
GPE = gravitational potential energy [J]

GPE is the energy of an object due to its position above Earth's surface

mgh = 1/2mv^2

elastic potential energy

energy stored as a result of applying force to deform an elastic object

EPE = 1/2kx^2
k = spring constant [N/m]
x = displacement of the spring from neutral position [m]
EPE = elastic potential energy [J]

conservation of Mechanical Energy:
KE1 + PE1 = KE2 + PE2
1/2mv^2[final] + 1/2k(change in s)[final] = 1/2mv^2[initial] +1/2k(change in s) [initial]

Multiple Spring

series

they have same force passing through them as each contributes to the total deflection

1/k total = 1/k1 + 1/k2 + 1/k3 + ... 1/kn

parallel

have same deflection and total force is split among them, for springs in parallel individual spring rates add directly

k total = k1 + k2 + k3 + ....+ kn