Is There an Upward Force Acting on a Rock When It's Dropped from a Cliff?

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When a rock is dropped from a cliff, the only force acting on it at the moment of release is the downward force of gravity. As the rock falls, air resistance begins to act upward, but gravity remains the dominant force. Eventually, when the rock reaches terminal velocity, the forces of gravity and air resistance become equal. This means that while air resistance does act upward, it is not significant until the rock is in motion. The discussion confirms that at the moment of release, only gravity is acting on the rock.
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Homework Statement


I have to draw a force diagram for a rock dropped off a cliff at the moment of release.
Is there any force acting upward on the rock at the moment of release?


Homework Equations


none


The Attempt at a Solution


I know the force of gravity acts downward on the rock. My thinking is that the only force acting on the rock at the moment of release is gravity downward, then as it falls there is air resistance upward and a greater force of gravity downward. When a rock hits it's terminal velocity however the forces of gravity and air resistance are equal. Is this correct?
 
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Hi cheerspens! :smile:
cheerspens said:
I know the force of gravity acts downward on the rock. My thinking is that the only force acting on the rock at the moment of release is gravity downward, then as it falls there is air resistance upward and a greater force of gravity downward. When a rock hits it's terminal velocity however the forces of gravity and air resistance are equal. Is this correct?

Equal and opposite! :biggrin:

Otherwise, completely correct! :smile:​

(i assume you're supposed to ignore the atmospheric pressure all round the rock :wink:)
 

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