Some picnickers stop at a convenience store to buy food, including bags of potato chips. They then drive up into the mountains to their picnic site. When they unload the food, they notice that the bags of chips are puffed up like balloons. Why did this happen?

Due to reduce in atmospheric pressure at height

Explanation:

According to simple physics, the greater the altitude the lesser will the be atmospheric pressure. When picnickers, went up on a mountain, at height the atmospheric pressure is reduced, the air pressure inside the bag being more than outside,(it became more because initially the bags were packed inside a factory that had the same pressure as that of normal surroundings) it caused the chips bag to puff up like balloon

Because of a change in pressure level

Explanation:

As we climb to higher altitudes (or heights), the air pressure around us drops.

When the potato chip was produced and sealed in bags, it was done at a lower altitude with a certain pressure level. By climbing to new altitudes (with a lower level of pressure), the air pressure within the bag of potatoes chips will try to normalize itself with the the pressure at the new altitude.

This is why the bag puffs up.

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Explanation: