How does the weight depend on position and time? Since this turns out to ignore effects of our position relative to and our distance from the center of the earth, we'll call this approximation flat-earth gravity. We'll also restrict our observations to a lab room - not changing our position or height very much.

Since air resistance depends on velocity, this also means we won't look at objects going very fast. This means we can ignore the 1/ r 2 fall off of gravity, since the r is our distance to the center of the earth - about 2/π x 10 7 meters - and we won't be changing that distance by a significant amount. And we'll drop them only at most a few meters. Imagine a series of spheres about 2 inches in diameter having masses ranging from about 1/4 of a kg to a couple of kgs. This means we'll use dense objects and we won't drop them very far - no more than a couple of meters. And once we have a good idea about how gravity works, we'll go back and explore objects falling with air resistance.įor this page, then, we'll look at objects for which air resistance seems to have not much of an effect. In order to try to learn just about gravity and not about a mixture of gravity and drag, let's focus on objects where it seems that the effect of air resistance is much less than the effect of gravity. And the air can exert a resistive force on the object ( viscosity or drag). But we know that in addition to the object being pulled down - its weight - it's touching something: the air. A crumpled up piece of paper will fall more slowly than a lead brick. If we drop a variety of objects, we observe that they all fall to the ground, but some fall more slowly than others. Look at how many dangerous bends there are in the text below! Our brain tends to create useful shortcuts that quickly give us the right answer in particular situations, but that don't generalize well and may be inconsistent with each other. Although we have lots of experience with gravity, reconciling our experience with the framework of Newton's laws is a bit tricky. Let's try to make sense of what this force is and how it behaves by doing some observations ( phenomenology). Every object seems to be pulled straight down, and if we hold it out and release it, it will fall to the ground. One of the forces we listed in going through our list of what interactions could change an object's velocity was weight.

Flat earth gravity theory