Arthur is testing how well various types of disinfectants can kill e. coli bacteria. he starts with a petri dish that is covered with e. coli. he puts exactly one milliliter of each different disinfectant at a different location on the petri dish. if a disinfectant works, it will eliminate the bacteria in the area in which it was placed. two days later, arthur will measure the amount of bacteria that has been cleared out by each disinfectant. which of the following is a variable in this experiment? a. the type of disinfectant used b. the type of bacteria used c. the petri dish used d. the length of time that the disinfectant is used

Many machines- including inclined planes such as ramps- increase the strength of the force put into the machine but decrease the distance over which the force is applied.

Suppose that two tanks, 1 and 2, each with a large opening at the top, contain different liquids. a small hole is made in the side of each tank at the same depth 1.57 m below the liquid surface, but the hole in tank 2 has 2.49 times the cross-sectional area of the hole in tank 1. (a) what is the ratio ρ1/ρ2 of the densities of the liquids if the mass flow rate is the same for the two holes? (b) what is the ratio rv1/rv2 of the volume flow rates from the two tanks? (c) at one instant, the liquid in tank 1 is 14.9 cm above the hole. if the tanks are to have equal volume flow rates, what height above the hole must the liquid in tank 2 be just then?

In an experiment, how can i change human errors? be specific.