energy

917

Pot of water
Heavy water played an important role in the development of the atomic bomb. What is heavy water?

960

wood and ashes
The wood in this pile will be reduced to this much ash when it is burned. What happens to the rest of the mass from the wood?

961

lighter
When I was growing up, lighters made a spark by rubbing a metal wheel across a flint (which was not really made out of flint.) Lighters like this one ignite the flame in a different way. How is the gas ignited?

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