How would an object in space "fall"? (You mentioned a meteor collision - what would cause the meteor to fall?)

Gravity still acts on objects, even though they are in space. No matter how far you get from the earth, it still pulls on you, albeit less strongly than it does when you are nearby. Thus if you were to take a ball billions of miles from the earth and let go, it would slowly but surely accelerate toward the earth. As long is nothing else deflected it en route, the ball would eventually crash into the earth's surface. Even objects that are "in orbit" are falling; they just keep missing one another because they have large sideways velocities. For example, the moon is orbiting the earth because, although it is perpetually falling toward the earth, it is moving sideways so fast that it keeps missing.

How do objects on earth accelerate downward at the same speed regardless of their mass?

What you mean here is that they accelerate downward at the same rate ("speed" has a particular meaning that isn't so well suited to discussions of acceleration). This fact comes about because, although massive objects are harder to accelerate, they also experience more weight. Thus a huge stone will fall at the same rate as a small rock because the stone will be pulled downward more strongly by gravity and that extra pull will make up for its greater inertia.

I don't understand the difference between mass and weight.

Mass is the measure of an object's inertia. You have more mass than a book, meaning that you are harder to accelerate than a book. If you and the book were each inside boxes, mounted on wheels, I could quickly determine which box you were in. I would simply push on both boxes and see which one accelerated most easily. That box would contain the book and you would be in the box that's hard to accelerate. Weight, on the other hand, is the amount of force that gravity (usually the earth's gravity) exerts on an object. You weigh more than a book, meaning that the earth pulls downward on you harder than it does on the book. Again, I could figure out which box you were in by weighing the two boxes. You'd be in the heavier box. So mass and weight refer to very different characteristics of objects. They don't even have the same units (mass is measured in kilograms, while weight is measured in newtons. But fortunately, there is a wonderful relationship between mass and weight: an object's weight is exactly proportional to its mass. Because of this relationship, all objects fall at the same rate. Also, you can use a measurement of weight to determine an object's mass. That's what you do when you weigh yourself; you are trying to determine how much of you there is-your mass-but you are doing it by measuring how hard gravity is pulling on you-your weight.

Does air resistance affect horizontal 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 degree angle from horizontal in order to make it travel as far as possible. Actually, the air has even more complicated effects on spinning balls, as we will discover in a couple of weeks.

If you jump off of a diving board, are you exerting force on the board or is it exerting force on you?

Actually, as you stand on the end of the board or as you push off from its end, you are pushing on the board and it is pushing back on you. The forces you exert on one another are exactly equal in amount but opposite in direction. That observation is called Newton's third law of motion and is the real meaning behind the phrase "for every action there is a reaction."

I can accept that weight is a force, but it doesn't seem to follow common sense to me.

It would seem like a force if you had to lift yourself up ladder. Imagine carrying a friend up the ladder; you'd have to pull up on them the whole way. That's because some other force (their weight) is pulling down on them. But when you think of weight as a measure of how much of you there is, then it doesn't seem like a force. But here is where the relationship between mass and weight comes into play. Mass really is a measure of how much of you there is and, because mass and weight are proportional to one another, measuring weight is equivalent to measuring mass.

Even though all objects supposedly accelerate, due to gravity, at the same rate, feathers do not seem to comply with this. What factor calculates into the feather's acceleration, besides air resistance which all objects in the same condition have equally?

Actually, air resistance doesn't affect all objects equally. The feather has so much surface area that it pushes on the air very strongly and the wind pushes back. For an object with very little mass and weight, the feather experiences an enormous amount of air resistance and has great difficulty moving through the air. That's why it falls so slowly. If you were to pack a feather in a tiny pellet, it would then fall just about as fast as other objects. Similarly, you fall much more slowly when your parachute is opened because then it interacts with the air much more effectively.

Doesn't weight have resistance to acceleration?

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. Clearly, an object that has great weight also has great mass and is therefore hard to accelerate. But 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 pound because of the incredibly intense gravity. That golf ball would still accelerate easily because its mass is unchanged. Only its weight is 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.

Is there a fixed amount of force in the universe?

No, forces generally depend on the distances between objects, so that two objects that are moving together or apart will experience different amounts of force as the move about. As a result, the total amount of force anywhere can change freely. But there are quantities that have fixed totals for the universe. We will encounter these so-called "conserved" quantities very soon. The most important of these is energy.

Why is 45 degrees the ideal balance to throw something the greatest distance if gravity is acting on the vertical component and not the horizontal?

The 45 degree angle is a good balance because it gives the ball a reasonable upward component of velocity and also a reasonable down field component of velocity. The upward component is important because it determines how long the ball will stay off the ground. The down field component is important because it determines how quickly the ball will travel down field. If you use too much of the ball's velocity to send it upward, it will stay off the ground a long time but will travel down field too slowly to take advantage of that time. If you use too much of the ball's velocity to send it down field, it will cover the horizontal distances quickly but will stay of the ground for too short a time to travel very far. Thus an equal balance between the two (achieved at 45 degrees) leads to the best distance.

If you drop a penny from the Empire state building - could it really puncture a hole in a car because of its constant acceleration?

Maybe. If the penny falls sideways, so that it has as little air resistance as possible, it will reach about 280 km/h (175 mph). That speed ought to be enough to drive the penny into the car if its top is thin enough.

I still don't understand horizontal component of a ball thrown downfield. Does it have constant velocity and/or acceleration, even at the start?

Until you let go of the ball, you are in control of its velocity and acceleration, so let's focus on what happens after you let go. As soon as you do, the ball's motion can be broken up into two parts: its vertical motion and its horizontal motion. Horizontally, the ball travels at a constant speed because there is nothing pushing or pulling on it horizontally (neglecting air resistance). Vertically, the ball accelerates downward at a constant rate because gravity is pulling down on it. Thus the ball travels steadily forward in the horizontal direction as it fall in the vertical direction. Of course, falling can begin with upward motion, which gradually diminishes and is replaced by downward motion.

Why did you have to stand 4.9 m high to let a ball drop for 1 second before hitting the floor?

Because I know the exact relationship between the ball's height and the amount of time since it was dropped from rest. In particular, I know that a ball falls 4.9 m in its first second. As a simple argument for that result, think about the ball's speed as it falls: it starts from rest and, over the course of 1 second, it acquires a downward speed of 9.8 m/s. Its average speed during that first second is half of 9.8 m/s or 4.9 m/s. And that is just how far the ball falls in that first second: 4.9 m. By holding the ball 4.9 m above the floor, I arranged for it to hit one second after I dropped it. I certainly don't expect you to be able to make such an argument on your own; I just wanted you to know that it's possible to do.

If a projectile released or hit at a 45 degree angle should go the farthest, then why, in the game of golf, does the three iron (20 degree loft) hit a golf ball so much farther in the air than, say, a seven iron (approximately 45 degree loft) if the same technique and force are produced by the golfer? Is it backspin, shaft length, etc.?

It's backspin! Air pushes the spinning ball upward and it flies down field in much the same way as a glider. When you throw a glider for distance, you concentrate your efforts on making it move horizontally because the air will help to keep the glider from hitting the ground too soon. Similarly, the air holds the spinning golf ball up for a remarkably long time so that giving the ball lots of down field speed is most important for its distance. That's why a low-loft club like a three iron sends the ball so far.