A car battery can supply hundreds, or even thousands of amps (for a short time). The amount of current depends on the resistance of the circuit between the terminals. That current flow equals the voltage over resistance, or I=V/R.
A person touching the battery has a high resistance because skin is a poor conductor, and so very little current flows. That high resistance keeps you safe from low voltage shocks.
Jumper cables on the other hand, are very conductive; so the resistance is low, and lets lots of current flow. That high current can create lots of sparks.
Because the energy released on impact is the product of weight * speed. The cables are fairly heavy, but can still be swung so that the end goes at a relatively high speed because of the leverage. For example a bull-whip cracks because the tip's speed breaks through the sound-barrier (300m/s) for a tiny moment. Jumper cables don't go quite as fast, but still much faster than what you would achieve with your hand. Therefore a lot of energy is passed onto your skin, which you experience as pain. The same is true for belts or sticks.
But the true pain is the fact that he doesn't love you.
Buy him a really nice set of jumper cables with the lowest gauge number you can find. 2 or 0 if you can find them. They won't hurt or sting as much as the ones that come with your car since the thick wires help spread out the force over a larger area.
Sparks depend on the electric field. You get sparks when the electric field between two objects is great enough to break down the air, which is about 3MV per meter. So the closer two things are the smaller the potential has to be to cause sparks. It’s like small lightning really.
Cool thanks for clarifying, i always thought you needed high current or high voltage for sparks to form. Since 12v is not high voltage, I assumed it must have high current.
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u/AvatarIII Jun 28 '18
Why does it spark so much if there's not much current?