Question

what is the primary energy transfer that occurs when sandpaper blocks are rubbed together, causing them to warm up? light energy is converted into electrical energy. electrical energy is converted into light energy. motion and sound energy are converted into heat energy. heat energy is converted into motion energy.

Explanation:

When sandpaper blocks are rubbed together, there is motion (mechanical energy from the rubbing motion) and some sound (sound energy). Due to friction between the sandpaper surfaces, these forms of energy (motion - related mechanical energy and sound energy) are dissipated as heat. This is in line with the principle of energy conversion where one form of energy is transformed into another. Frictional forces act against the motion, and the work done against these forces results in an increase in the internal energy (heat) of the sandpaper blocks.

Answer:

Motion and sound energy are converted into heat energy.