Everything is measured in watts
currents + voltage
Power = energy/time
1 Watt power = 1 Joule energy/1second time
so also
1 Joule = 1 Watt * 1 second
Gravitational Potential Energy = mgh
m = mass ; g = gravitational acceleration = 9.8 m/s/s
h = height
(1 kg) * (9.8 (m/s) / s) * 1 meter = 9.8 Joules
Kinetic Energy = 1/2 mv^2
m = mass in kg ; v = velocity in meters/seconds
We can’t get out of a system that isn’t in the system in the first place
2nd law of thermodynamics = not all of the energy in a system will be available to do the work we want