Lava
Melted rock that has reached the surface of the Earth. Lava can ooze slowly like red-hot treacle, or fountain up into the air — it depends on what it's made of and how much gas is trapped inside.
Lever
A stiff bar that pivots around a point. A lever lets you use a small push at one end to produce a big lift at the other — or the other way around, depending on where the pivot is. Crowbars, wheelbarrows, and your own...
Load
A force or weight that a structure has to hold up. The engineers who build bridges have to think about lots of loads at once — the weight of the bridge itself, the vehicles crossing it, the wind pushing against it,...
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