Why is it nessesary to have an independent variable that is changed by the experimenter during an experiment

Debbie places two shopping carts in a cart corral she pushes the first cart which then pushes a second cart what force is being exerted

The experiment was repeated many years later but the gases were mixed in a different type of container. a white solid was obtained which was xenon fluoride. predict whether you think 1) krypton and 2) radon will react with fluorine. explain reasons for your predictions

Amoving company collects data about couches they move and displays the data in a table. the force along the ramp, the angle of the ramp, and the height the couch is raised to are shown. which statements correctly compare the work done to move the couches? check all that apply. the same amount of work is done for couches 1 and 3. the same amount of work is done for couches 2 and 3. the work for couch 1 is greater than the work for couch 2. the work for couch 2 is less than the work for couch 3. the work for couch 3 is greater than the work for couch 1. the work for couch 2 is greater than the work for couch 1.