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

the rolling friction is much less than the sliding friction
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
coal tar is a liquid and it flows in the barrel when it is rolled

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Physics
Negative feedback in amplifiers

Decreases bandwidth and decreases noise
Increases bandwidth and decreases noise
Decreases bandwidth and increases noise
Increases bandwidth and increases noise

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