Jerome places a bag of flour on a scale. The scale shows that the bag has a weight of 17 N. Which is the reaction force of the bag sitting on the scale?

The scale reading of 17 N means the scale pushes up on the bag with a 17 N force while the bag is at rest. By Newton’s third law, the bag pushes down on the scale with an equal, opposite force. So the reaction force is the 17 N force downward on the scale.

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