Static Electricity Legacy Problem #4 Guided Solution

Objects which are charged will exert attractive or repulsive forces upon each other. Objects which are oppositely charged will attract, and objects which are like charged will repel. Here we are given that we have two objects, a styrofoam plate and an aluminum dish, and they are both charged, one with negative and one with positive charge. We are given the amount of charge on the styrofoam plate and the aluminum dish. The unit C is the unit coulombs, signifying the quantity of charge. In equations we often represent this by q1 and q2. We are also given the distance which separates the centers of these two objects. It is 1.85 centimeters. That centimeter will become important later when we begin to solve the problem. Now what we wish to do is to calculate the force of attraction between these two objects. We need to use Coulomb's law equation to do that. Coulomb's law equation states that the force of attraction or repulsion is equal to k, the proportionality constant, multiplied by q1, multiplied by q2, divided by the d squared, d being the separation distance. Here in this problem that distance is 1.85 centimeters. Now we know that the proportionality constant k in the equation is 8.99 times 10 to the 9th, newtons times meters squared per coulombs squared. Given these units on the value k means that we need to substitute into our Coulomb's law equation the value of distance in units of meters, not centimeters. So before we begin our substitution we need to check our units and make sure all quantities are in the proper unit. The q1 and q2 values which are given are given in the right unit, coulombs, but the d is in units of centimeters. So before substituting we need to convert that to units of meters. I need to take the decimal place and move it two places to the left such that 1.85 centimeters becomes 0.0185 meters. Now I can substitute that into my equation being certain to square it and I should get the right answer.