| A | B |
|---|
| atomic number | a unique number for each element that equals the number of protons in an atom of that element |
| controlled variable | in an experiment, all the variables that are held constant |
| electric charge | a property that causes subatomic particles such as protons and electrons to attract or repel one another |
| electric force | the attraction or repulsion between electrically charged objects |
| controlled experiment | an experiment in which only one variable, the manipulated variable, is deliberately changed at a time |
| family of elements | a group of elements organized in the periodic table by their chemical properties |
| frictional force | the force exerted by a surface as an object moves across it |
| gravitational force | an attractive force that acts between any two objects |
