0:00:00.000,0:00:03.000 It's not like there are some real similarities between charge and mass. 0:00:03.000,0:00:07.000 Specifically, similarities between the electric force and the gravitational. 0:00:07.000,0:00:12.000 Let's do some comparison to see just how similar or how different these forces are. 0:00:12.000,0:00:15.000 First, let's analyze the cause of each force. 0:00:15.000,0:00:18.000 Well, the electric force is caused by charged objects 0:00:18.000,0:00:22.000 whereas the gravitational force well it's caused by massive objects. 0:00:22.000,0:00:25.000 Charge and mass are the causes of these forces. 0:00:25.000,0:00:29.000 What about the effect? What kind of object feels the effect of the electric force? 0:00:29.000,0:00:32.000 Well once again it's an object with a charge. 0:00:32.000,0:00:35.000 Likewise, gravitational force is felt by objects with mass. 0:00:35.000,0:00:38.000 Notice that we already see one similarity. 0:00:38.000,0:00:43.000 The thing that causes the force is the same as the thing that feels it. What about the force law? 0:00:43.000,0:00:46.000 And by force law I mean what's the equation that describes these forces? 0:00:46.000,0:00:49.000 Well with gravity we knew the force of gravity was proportional to 1 0:00:49.000,0:00:53.000 over your distance away from the mass of object that's causing the force. 0:00:53.000,0:00:57.000 In the case of the earth and the moon, r would be the separation between the two bodies. 0:00:57.000,0:01:02.000 With the electrical force, it turns out the force law is almost identical. 0:01:02.000,0:01:08.000 It's still proportional to 1 over r². So doubling the distance will decrease the force by a factor of 4. 0:01:08.000,0:01:13.000 What about the direction of force? Well for gravity, objects always attract each other. 0:01:13.000,0:01:17.000 In fact, it's this attraction that allows large bodies like the earth to form 0:01:17.000,0:01:21.000 because every little tiny chunk of rock is attracted to every other little tiny 0:01:21.000,0:01:27.000 chunk of rock and together they coalesce and form this wonderful beautiful sphere. 0:01:27.000,0:01:30.000 What about with electricity? This is where things get interesting. 0:01:30.000,0:01:36.000 With electricity, the direction is not always attractive. Sometimes it's repulsive. 0:01:36.000,0:01:41.000 And this one key difference is responsively for many of the fascinating 0:01:41.000,9:59:59.000 aspects of electricity which well we can learn about now.