When it comes to cool road trips and awesome driving exploits, Apollo astronauts David Scott, John Young, and Eugene Cernan pretty much have us all beat forever, seeing as how they drove on the Moon and all. At least the video up top gives some idea of what it was like to tool around the Moon.
The equivalence principle is one of the fundamental concepts behind gravitational theory and general relativity, and holds that gravity exerts the same force on objects of different mass.
Back in 1969, the Apollo 11 mission put mankind on the moon. It was a massive accomplishment. Two years later, though, people were getting bored. 40 years ago today, it become the moon buggy's job to make space fun again.