Which example best demonstrates how unbalanced forces change the speed of an object's motion? a) a child on a bicycle braking at a stop sign. b) a child singing a song. c) a child sitting in a chair reading a book. eliminate d) a child walking around the corner of a school hallway.

The correct answer is A.

Explanation:

Unbalanced forces change the speed of movement of an object because they act non-uniformly on the object to which they relate. When a child on a bicycle brakes on a stop sign, the brakes act unevenly on the wheel, causing an uneven decrease in speed. In this way, you lose the balance of the movement you had prior to braking.

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air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

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