Physics
Who enunciated the laws of planetary motion?

Nicolaus Copernicus
Galileo
Johannes Kepler
Isaac Newton

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Physics
It is easier to roll a barrel full of coal tar than to pull it because

coal tar is a liquid and it flows in the barrel when it is rolled
the full weight of the barrel comes into play when it is pulled
more surface area of the barrel is in contact with the road when it is pulled
the rolling friction is much less than the sliding friction

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