CalcSpace.com lets you build multi-line calculations and instantly see the results. It supports units of measurement, so it's great for physics and engineering. Sharing mechanism makes it easy to collaborate with other people.
x = 3
y = 8 / 2 = 4
g = 9.81m/s^2
m = 100kg + 45lb = 120.41165665kg
h = 6ft + 3in = 1.905m
// Potential energy:
E = m * g * h = [ Error: Expected square brackets [...] after last "="
m = 10kg
v = 7.2km/h = 2m/s
E = (m * v ^ 2) / 2 = [J] = 20J