Yes, it can be considered impressive that you can hear the whip-like sound when you swing your arms without forming your hand into a fist. This sound is known as the "whip-crack" or "whip-snap" sound, and it occurs due to the rapid acceleration and deceleration of the air when you move your hand through the air quickly.
The whip-crack sound is produced because of a phenomenon called the "sonic boom." When you swing your hand rapidly, it creates a shockwave as it moves through the air, and when the hand reaches the speed of sound (approximately 343 meters per second or 767 miles per hour at room temperature), the shockwave compresses the air molecules, generating a sharp and distinctive sound.
The fact that you can hear this sound without forming your hand into a fist suggests that you are able to swing your arm with sufficient speed to produce the shockwave and create the whip-crack sound. It's worth noting that not everyone can achieve this, as it requires a combination of factors such as the speed and technique of arm movement and the ability to create the right conditions for the sonic boom effect to occur.
However, keep in mind that generating the whip-crack sound by swinging your arm rapidly can be potentially harmful. The rapid movement may cause strain on your muscles and joints, and the sonic boom effect can be loud and may even cause discomfort to those around you. So, while it may be impressive, it's essential to be mindful of your movements and considerate of others in your surroundings.