The hitter just hit the ball with a bat. He wants the ball to travel as straight as possible

A. In the illustration above, are the forces acting on the ball balanced or unbalanced? If unbalanced, which force is most powerful.

B. Is friction acting on the ball? If so, explain how it may change the ball’s speed and direction.

A) Unbalanced

B) Yes

Explanation:

A)

Here we are analzying the situation just after the ball has been hit by the bat.

In this situation, there are only two forces acting on the ball:

- The force of gravity, acting in the downward direction, of magnitude (where m is the mass of the ball and g the acceleration due to gravity)

- The friction due to the air (air resistance), acting in the direction opposite to the motion

As we can see, the two forces act in different directions: according to the rules of vector addition, this means that the resultant force on the ball is different from zero; therefore, the net force on the bat is unbalanced.

We can also say that the stronger force is the force of gravity (in fact, the air resistance is generally small).

B)

Yes.

As we said, apart from gravity, there is another force acting on the ball: friction (or better called air resistance).

without the presence of air resistance, the ball would follow a parabolic trajectory, due to the combination of:

- The horizontal motion, which is uniform (no forces acting in this direction)

- The vertical motion, which is accelerated (due to the presence of the constant force of gravity)

However, in real life we also have to consider the presence of the air resistance. The direction of the air resistance is opposite to the motion of the ball: as a result, it will have the following effect:

- It will decrease the speed of the ball, as the force does negative work on the ball

- It will decrease the maximum height and the range of the ball, as the ball will decrease its speed faster

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