The decline bench press gives you have a limited range of motion. You can use more weight because of both mechanical advantage and less total work being performed. By only bringing the bar down to your lower chest, you severely limit the distance you move the bar.
The time difference that you sense is due to the way sound and light travel. Light travels extremely fast (300,000,000 m/s). In fact, it is faster than anything else. Sound travels at a measly 343 m/s through air. Therefore we can see light in an instant, but it takes a while to hear thunder. Sound has another disadvantage because it tends to bounce off molecules in the air. This makes the sound travel in all different directions.
Speed of sound. The speed of sound is the distance travelled per unit time by a sound wave as it propagates through an elastic medium. In dry air at 0 Â°C (32 Â°F), the speed of sound is 340.27 metres per second (1,116 ft/s; 1,225 km/h; 761 mph; 661 kn).