1. Example : ( Physics Classroom ) Two balloons are charged with an identical quantity and type of charge: -6.25nC. They are held apart at a separation distance of 61.7cm. Determine the magnitude of the electrical force of repulsion between them. Interactions When we are talking about interactions we can consider 2 cases: when objects come in contact with each other or when objects do not come in contact with each other. It is important to realize that when objects are at a distance from one another, fields cause interactions. Equati on : This is a mathematical expression of charge interactions. Multiply the charges and Coulomb’s constant and then divide by the radius. F = force of the interaction in Newtons Q 1 = the charge of object 1 in Coulombs Q 2 = the charge of object 2 in Coulombs D = the distance between the centers of the two objects in meters k = Coumlomb’s Law constant changes depending on the medium of objects For air k = 9.0 x 10 9 N m 2 /C 2 Coulomb’s Law Coulomb’s Law Electric Force Interactions Sara Mills STEM 962: Final Presentation Framingham State University Contact Information NGSS PS2.B: Types of Interactions Objects in contact exert forces on each other. (3-PS2-1) Electric and magnetic forces between a pair of objects do not require that the objects be in contact. The sizes of the forces in each situation depend on the properties of the objects and their distances apart and, for forces between two magnets, on their orientation relative to each other. (3-PS2-3),(3-PS2-4) Static Electrici ty Electric Fields are the amount of electric force per unit of charge. In this diagram you can see how electric forces interact. The direction of the force moves outward from a positive charge and inward toward a negative charge. Looking at a single point charge simplifies things and you can see that the charge radiates in all directions. This creates a spherical equipotential surface. Electric force is a vector quantity meaning that it has magnitude and direction. Electric Fields and Point Charges The Law Basically this law states that the magnitude of the force and the distance of the objects are inversely related (Physics Classroom). To determine the strength of the interaction three variables should be considered: the charges of both objects and the distance between the objects. The closer the charges are together the greater the attraction will be and the further the charges are apart, the greater the repulsion. Coulomb’s Law is similar to Newton’s gravitational law only involved electrical charges. Application / Calculation s The above diagram shows two balloons that have been rubbed with animal fur and have become negatively charged. The balloons are repelling each other because of their negative charges. (Gravity and tension are also forces acting upon the balloons.) Using Coulomb’s Law one can calculate the force of the interaction. Try it ! Two balloons with charges of +3.37 x 10 -6 C and -8.21 x 10 -6 C attract each other with a force of 0.0626 Newton. Determine the separation distance between the two balloons.