There used to be volcanoes on the Moon. ... Scientists think that the Moon's interior remained hot enough to produce magma for about a billion years after the Moon formed. The lava that came out of the Moon cooled quickly, and formed fine-grain, dark rocks called basalt.
1. flying a plane (friction between air and plane) 2. ice skating (friction between ice and skate blade) 3. swimming (water & skin) 4. rowing a boat (water and boat)
