 In the last couple of videos, we learned about some common everyday forces and how to quantify them. We're now going to slightly increase the complexity and work through some problems where we might have multiple forces acting on an object. For the first problem, let's consider an apple falling from a tree. The first step is always to draw a free body diagram. It's easiest to draw the object as a single point, representing its centre of mass. In this case, the only force acting is gravity downwards, equal to mg. We will ignore the drag force for now. We can apply Newton's second law. The net force is equal to the mass times the acceleration. So in this case, the net force is just equal to mg. So mg equals ma. The striking thing about this result is that when there is no air resistance, the acceleration is independent of the mass of the object. This is what you saw in the video with the feather and the hammer being dropped on the moon. In this problem, because of the small distance and the shape of the apple, it's a reasonable assumption to ignore the drag force. But that's not always the case.