AM radio stations have so much power that even a short wire can catch enough voltage from such strong electric field. If you happened to have an optimally long - say 75 meters high - whip antenna you perhaps could listen with a rectifier + a high efficiency speaker or headphones (normal speakers and headphones today have very low efficiency i.e. very low audio dB output vs input watt). Crystal receivers were common say 100 years ago. With them people had big antennas if they did not live near the station. They could listen with efficient headphones stations from hundreds or even thousands of miles away and a nearby station could be received so strongly with no amplification that everyone in the same room could hear it.
Actually even your few feet wire antenna is not needed in many cases. AM receivers have on their circuit boards specially designed ferrite core coils (=ferrite antenna) in resonant circuits and they catch enough excitation from the magnetic field of the radiowave. 100 years ago ferrite materials were not common. AM receivers could have about 1...4 sq.feet size coil in their input stage bandpass filter resonant circuit to catch the signal from the air. It was called loop antenna. It worked and works if the receiver has at least some amount of amplification. Non-amplified crystal radio could catch something audible with loop antenna if the AM station was within 1 mile.
Optimal receiving antennas are really needed if the transmitter is distant or it has low power. Unfortunately in modern environments all kinds of electric noises (caused by electric machines and computers) are so strong that there's no hope to hear anything useful if the transmitters have low power or they are too distant. Big receiving antenna doesn't help if it's in a noisy environment. A low power transmitter could well be enough if the receiver (with big antenna) was in the middle of Sahara or Atlantic ocean.
A comment by John Doty claims that it's not true. It says that a sensitive receiver + optimal antenna can nowhere catch weak nor distant stations well because in MW band the noise is very high without any urban environment. The noise is born in the sky, mostly it comes from static electricity discharges when different temperature and moisture airflows rub each other. The strongest form of such discharges is lightning
A shopping guidance: Go to an antique book store and search for old, say 1950s and 1960s radio building hobbyist books and magazines. Even older ones are ok if you are interested in vacuum tube radio constructions.
ADD: I've got the next comment:
I see, since it is AM its not about getting the whole signal, but rather enough energy to convert the radtation signal to electrical signal, its less dependent on antenna size. whereas FM relies on getting the entire wavelength or at least a integer divisor for information to be transferred. makes sense since FM is in the 80 MHz range as compared to 500 kHz range for AM – Waterbloo
To stay in the frame of science and physics I must add that AM radio stations were built with high power to reach as much audience as practically possible. Governments saw early that it's ideal to be heard also in foreign countries. It's useless to build as powerful FM radio stations.
FM has theoretical benefits over AM. FM filters out some noises if the signal strength is good. But FM needs so much frequency bandwidth that using it at low frequencies like 1MHz would leave room only for few radio stations. The MW band has room for about 100 AM stations even if they were so powerful that they could be heard globally (see NOTE1)
The need of high bandwidth is the reason why FM stations have higher frequency, say 95 MHz averagely. But high frequency prevents radiowaves to propagate curved paths over the horizon. That's because the ground and atmosphere affect differently to different frequencies. For that reason the horizon is the limit for the FM. Very high, say 300...1000 feet high towers below the transmitting antennas are built, but the maximum range of FM radio station still is well below 100 miles. So it's useless to have more power than the by horizon limited range needs.
NOTE1: Local AM stations exist. The total number of AM stations is much higher than the mentioned 100. That's possible, because in the daytime the radiation from the sun makes the upper atmosphere slightly conductive in such way that in the MW band over the horizon transmissions attenuate quickly. Local AM stations have quite low power and they are quiet between the sunset and the sunrise. In the night they would severely disturb each other because their frequencies overlap.
