Answers:
The forces have opposite directions
The forces have equal magnitudes
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Step-by-step explanation:
Imagine a bucket of water being held up by a rope.
Gravity pulls down on the bucket with a constant force. The reason why the bucket doesn't fall to the ground is because the tension in the rope is holding it up.
More specifically, the force of the rope's tension is exactly matching the force of gravity. So we have equal magnitudes here. However, the force vectors point in complete opposite directions. Gravity points down and the tension of the rope points up. The two opposite directions cancel out to create balance and that's why the object doesn't move. It has velocity = 0 which is considered a constant velocity even though it's not something like 3 m/s.
If the forces acted in the same direction, then the magnitudes would add up to accelerate the object (either downward or upward). However, the bucket stays fixed in place, so it's clear that the vectors must be opposite in nature.
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Now consider a skydiver. At some point of the descent, the skydiver will hit terminal velocity. This is the fastest s/he can fall because the force of gravity pulling down counterbalances perfectly with the upward force of wind/air resistance pushing upward. The air is resisting the downward motion being a form of friction. In this case, the magnitude of the gravitational force is the same as the magnitude of the upward air resistance.
Unlike the bucket of water, the skydiver is of course moving. They are moving at a constant velocity since they cannot accelerate any faster. Hence the name "terminal" meaning "the final or ending velocity". It is when the parachute is deployed that will apply a much greater upward force, which then slows down the downward velocity to allow the skydiver to safely land.
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In both examples, we have a constant velocity happening when the vectors pull in equal amounts but in opposite directions. Think of it like a tug-of-war to keep everything balance. If there is an imbalance of any kind, then acceleration will happen.