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Darrel Deval the skydiver pulls the chord of his parachute. The forces acting upon Darrel and his parachute are shown in the diagram at the right. From this diagram, one might infer that ...
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Net Force and Direction of Acceleration
Newton's second law relates the acceleration of an object to the net force exerted upon the object. The acceleration is directly proportional to the net force and in the same direction as the net force.
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Speeding Up, Slowing Down, and the Direction of Acceleration:
If an object is slowing down, then the direction of its acceleration is opposite the direction that the object is moving. A falling object (downward moving) with an upward acceleration is slowing down.
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Several lines of good reasoning are required to be successful on this question. The reasoning patterns are described below:
- The forces acting upon an object determine the object's acceleration - both the magnitude and the direction of the acceleration. If there is more downward force than upward force, then the object has a downward acceleration. And if there is more upward force than downward force, then the object has an upward acceleration. A free-body diagram is a useful tool for communicating information about the direction of an object's acceleration.
- Air resistance is a resistance force that opposes the motion of an object. If an object is moving to the right, then the air resistance force is to the left. If an object is moving up, then the air resistance is down. Knowing the direction of air resistance allows one to determine the direction that an object is moving.
- Knowing the direction that an object is moving and knowing the direction that it is accelerating will provide sufficient amount of information about whether the object is slowing down or speeding up (see Know the Law section).
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