What is the independent and dependent variable. After learning about electricity, a student wants to see if electricity flows better through different materials. Our wonderful student has different materials: copper wire, aluminum wire, carbon fiber, and gold wire. The student attaches a small lightbulb to a 9 volt battery, and uses each wire to see how bright the lightbulb lights up when connected to each material.

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it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me