If you make an electromagnet using a battery circuit and a steel nail how can you increase its magnetic strength?

By wrapping a conductive wire around a steel nail and adding a battery, you've created what is known as a solenoid. This solenoid produces a magnetic field around the nail when a current is passed through it. There is an equation that relates the various properties of the solenoid together to determine the strength of the magnetic field; in short, to increase the strength, you can shorten the overall length of the coiled wire (not the wire itself, but the length of the coil around the nail), increase the current flowing through the wire, or increase the number of turns/loops of wire around the nail.

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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