The physics and science of falling balls
Yes. A ball thrown horizontally gradually loses its downfield component of velocity. For that reason, you must throw a ball somewhat below the 45° angle from horizontal in order to make it travel as far as possible. Actually, the air has even more complicated effects on spinning balls.
If the ground is level and there were no air resistance, the answer would be no. The flight of the ball is perfectly symmetric. It rises to a maximum height in a parabolic arc and then returns to the ground as the continuation of that same parabolic arc.
However, if the ground isn’t level, then the angle it hits the ground at might be different. For example, if you toss a ball almost horizontally off a cliff, it will hit the ground almost vertically. Horizontal and vertical are two very different directions.
Air resistance also tends to slow a ball’s motion and it’s particularly effective at stopping the downfield component of its velocity. Gravity makes sure that the ball descends quickly, but there is no force to keep the ball moving downfield against air resistance. The result is that balls tend to drop more sharply toward the ground. When you hit a baseball into the outfield, it may leave your bat at a shallow angle but it will drop pretty vertically toward the person catching it.
Finally, if the ball is spinning, it can obtain special forces from the air called lift forces. These forces can deflect its path in complicated ways and are responsible for curve balls in baseball, slices and hooks in golf, and topspin effects in tennis.
Here is why the two situations are different:
In the first case, the car is traveling on a road with a changing slope. Because the road’s slope changes, the car’s direction of travel must change. Since velocity includes direction of travel, the car’s velocity must change. In short, the car must accelerate. Picture a hill that gradually becomes steeper and steeper—the car’s velocity changes from almost horizontal to almost vertical as the slope changes.
In the second case, the bicycle is climbing a smooth, straight hill at a steady speed. Since the hill is smooth and straight, its slope is not changing. Since the bicycle experiences no change in its direction of travel or its speed, it is traveling at a constant velocity and is not accelerating.
No, weight measures a different characteristic of an object. Mass measures inertia (or equivalently resistance to acceleration). But weight is just the force that gravity exerts on an object. While an object that has great weight also has great mass and is therefore hard to accelerate, it’s not the weight that’s the problem. To illustrate this, imagine taking a golf ball to the surface of a neutron star, where it would weigh millions of pounds because of the incredibly intense gravity. That golf ball would still accelerate easily because its mass would be unchanged. Only its weight would be affected by the local gravity. Similarly, taking that golf ball to deep space would reduce its weight almost to zero, yet its mass would remain the same as always.
Yes. When you skydive, your velocity doesn’t increase indefinitely because the upward force of air resistance eventually balances the downward force of gravity. At that point, you reach a constant velocity (called “terminal velocity”). Just how large this terminal velocity is depends on your shape. It is possible to increase your terminal velocity by rolling yourself into a very compact form. In that case, you can overtake a person below you who is in a less compact form.