Omar wants to determine if the mass of a model rocket affects how long the rocket is able to stay up in the air. To do this, he constructs three identical rockets and then fills two of the rockets with varying amounts of sand to add mass. He then launches the rockets one at a time and times how long they are able to stay airborne. What is the test variable (independent variable) in Omar's experiment?

To do this, he constructs three identical rockets and then fills two of the rockets with varying amounts of sand to add mass.

Explanation:

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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