You said that from the moment the ball leaves your hand (after you threw it upward), it accelerates downward even though you threw it upward. However you then said that the ground (gravity) pushed on your foot to make you accelerate, so why would you also not be accelerating in the opposite direction, like the ball? Why would you not accelerate in the direction in which you were pushed?

I got ahead of myself by using forces I had not yet introduced. I was using friction to push me horizontally across the floor! Here is the complete story:

When I tossed the ball upward and it was rising, gravity was pulling downward on it and it was accelerating downward. But when I obtained a force from the ground, it was not gravity that exerted that force on me; it was friction! As we will discuss in a few days, whenever you try to slide your foot across the floor toward the left, friction pushes your foot toward the right. In class, I traveled toward the right because I was being pushed by friction toward the right. I was actually accelerating in the direction I was pushed, just as you expect.

When accelerating, can you decelerate by going in a direction that is not opposite (your velocity)? For example, going north can you decelerate by going east?

Decelerating is a very specific acceleration—always in the direction opposite your velocity. If you were heading north and accelerated toward the east, your velocity would soon point toward the northeast. It would have some northward aspect because you were initially heading north and hadn’t yet accelerated toward the south. It would have some eastward aspect because you had initially been heading neither eastward nor westward and had since accelerated toward the east.

On the other hand, if you were heading north and then turned toward the east, you would have lost your northward velocity and obtained an eastward velocity. This “turning” would have involved a southward acceleration (to get rid of the northward velocity) and an eastward acceleration (to acquire an eastward velocity).

Warner Brothers has been misleading children! The coyote and the anvil hit the ground at the same time!

You’re exactly right. Occasionally one of those cartoons shows the coyote falling with the anvil directly above his head and the distance between them remaining constant, which is what should happen (ignoring air resistance). But more often, the coyote falls much faster than the anvil, hits the ground first, and is then pounded by the anvil. It sure would be neat to live in a cartoon—the laws of physics just wouldn’t apply.

How was Newton able to prove inertia with gravity and friction still being present? Why didn’t people think he was crazy? Did he have some type of vacuum or something? – JP

Actually, it was Galileo who first realized that objects have this tendency to continue moving at a steady rate in a straight-line path—what we call “inertia.” He deduced this fact by studying the motions of balls on ramps. He noted that a ball rolling down a slight incline steadily picked up speed while a ball rolling up a slight incline steadily lost speed. From these observations he realized that a ball rolling along a level surface would roll at a steady speed indefinitely, where it not for friction and air resistance. He was aware that friction, air resistance, and gravity were disturbing the natural motions of objects and had figured out a way to see beyond them. But it wasn’t until Newton took up this sort of study that the idea of forces and their effects was properly developed. Overall, it took almost two thousand years, from Aristotle to Newton, for the incorrect idea that objects tend to remain stationary when free of forces to be replaced with the correct idea that objects tend to continue at constant velocity when free of forces.