To convert miles per hour (mph) to feet per second (ft/s), you can use the following conversion factor: 1 mph = 1.46667 ft/s.
Therefore, if a pitcher throws a baseball at 90 mph, the ball's velocity in feet per second can be calculated as:
90 mph * 1.46667 ft/s = 132 ft/s
So, the ball would be traveling at approximately 132 feet per second.