Because the electromagnetism pushes the paper cone of the speaker, the paper cone pushes the air, and the air pushes the stage made of cardboard to vibrate, so the little man on the stage can also vibrate. The sound of the speaker is made by the vibration of the paper cone. Since your stage (paper) is vibrated by the vibration of the speaker, the little man on it will jump with the rhythm.

It explains that vibration occurs when sound is emitted, and it also indirectly explains that sound produces energy; the sound emitted by the speaker propagates along the medium, and the paper vibrates due to air vibration.

Extended information:

Junior high school electromagnetic knowledge

1. The interaction between magnetic poles: magnetic poles with the same name repel each other, and magnetic poles with different names attract each other.

2. Regulation of the direction of the magnetic field lines: Outside the magnet, the magnetic field lines start from the N pole of the magnet and return to the S pole.

3. Geomagnetic field: The geomagnetic north and south poles are exactly opposite to the geographical north and south poles, and their positions are slightly deviated. That is the opposite of magnetic theory.

4. Oersted's experiment shows: There is a magnetic field related to the direction of the current around the energized conductor, which is the magnetic effect of the current.

5. Factors that affect the magnetic strength of electromagnets: current size and number of coil turns. If the number of turns of the coil is the same, the greater the current of the electromagnet, the stronger its magnetism; when the current is constant, the more turns of the coil of an electromagnet with the same shape, the stronger its magnetism.