Speed of Light
Speaking of the speed of light,we often hear the "Speed of light is 7.5laps around the earth in a second." (Another common metric,going the time it takes light to go from the sun to the earth is about 8minutes 20seconds, from the moon to the earth is 2seconds,and so on.) The Circumference of the earth is about 40000km,therefore light travels at a speed of about 300000km in a second. Strictly speaking,light travels 299792458 m/s in a vacuum.Galileo Galilei's attempts to measure the speed of light is famous among humans. He tried to measure the time that light took going back and forth using two ramps that were far away. However,it was failure because light is very fast.