You have three small balls, each hanging from an insulating thread. You find that balls 1 and 2 attract one another and that balls 2 and 3 repel one another. Which ball, if any, is possibly neutral

If gases like carbon dioxide and methane make up less than 1% of the total atmosphere, why is it important for scientists to monitor changes in percentages of these gases?

70 give a real life example showing how sensory neurons work with the motor neurons

Aresistor with an unknown resistance is connected in parallel to a 9 ω resistor. when both resistors are connected in parallel to an emf source of 21 v, the current through the unknown resistor is measured with an ammeter to be 4 a. what is the resistance of the unknown resistor? answer in units of ω.