Mr. Obama rarely plays with other politicians - though he has played 7 times with Vice President Biden. In a fence-mending gesture, Mr. Obama invited then-House Speaker John Boehner to play on one occasion in June 2011 along with Gov. John Kasich, both Ohio Republicans.
Here are some ways to classify coal (by grouping it with similar types of rocks): Because slag formed from lava-like melted rock, it's sort of like an igneous rock -- but because humans made the melt, it's not a true igneous rock. So, we made up a new classification for slag: We call it a pseudo-igneous rock (pronounced SUE-doe ig-NEE-us).
Ice melts when heat energy causes the molecules to move faster, breaking the hydrogen bonds between molecules to form liquid water. In the melting process, the water molecules actually absorb energy. This is why an ice cube melts more quickly on the outside and retains its coldness and solidity longer at the center: melting is a cooling process. As more heat is introduced, the ice will continue to melt, and if the temperature exceeds the boiling point, about 100 degrees Celsius (212 degrees Fahrenheit), more hydrogen bonds between water molecules will break completely, creating water vapor.