OpenQuery25

course PHY 121

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025. `query 25*********************************************

Question: `qprinciples of physics and gen phy 4.26 free-body diagram of baseball at moment hit, flying toward outfield

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Your solution: A baseball is hit because the ball and the bat collide and the bat exerts a force on the ball that reverses its direction of motion (from pitched toward home to flying away from home plate). As the ball travels (mostly) up and away, it will gradually sink because gravity is working on the weight of the ball through the air. Of course there are many different paths the ball can take, from a more linear to a more parabolic route (during which there would be a point where the velocity = 0 as the ball peaks).

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Given Solution: `a** Gravity exerts a downward force equal to the weight of the ball.

While in contact with the ball, and only while i contact, the bat exerts a normal force, which pushes outward along a line originating from the central axis of the bat. This force is perpendicular to the surface of the bat at the point of contact.

Unless the direction of the ball is directly toward the center of the bat, which will not be the case if the ball is hit at an upward angle by a nearly level swing, there will also be a frictional force between bat and ball. This frictional force will be parallel to the surface of the bat and will act on the ball in the 'forward' direction.

COMMON STUDENT ERROR: The gravitational force and the force exerted by the ball on the bat are equal and opposite.

The force of the bat on the ball and the gravitational force are not equal and opposite, since this is not an equilibrium situation--the ball is definitely being accelerated by the net force, so the net force is not zero. **

COMMON STUDENT ERROR: Confusing motion in a direction with force in that direction.

There is no force associated with the motion of the ball. The velocity of the ball in will remain unchanged if there is no net force on the ball. Furthermore, if the is net force has zero component in the x direction, the x velocity remains unchanged; the analogous statement holds for the y direction.

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Self-critique (if necessary):OK

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Self-critique Rating:

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