Question: Does a cricket ball change velocity during flight?
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It would be an intimidating experience to face up to a serious pace bowler. They run in towards the crease and fling the ball down the pitch. Fast bowlers can do around 140km/h, and the best have clocked 160km/h.
Their arm rotating gives them a mechanical advantage, and the longer, the better. That's why you can lob a ball to your dog a long way, using one of those tennis ball throwers.
At this speed the ball has to work to cleave the air in front as well as drag a pocket of air behind. Terminal velocity is 123km/h, so without a continuous shove, it'll rapidly slow to that speed.
Then it hits the ground, where it scrubs off another 30-40 per cent. When it gets to the batter after half a second in flight, it'll be travelling at under 90km/h. After the bounce, the batter has only 100−200 milliseconds to predict where it's going.
But they have to have made up their mind before then, which gives them only about 400 milliseconds. Having made their best guess, they must swing the mass of the bat into the path of the ball, at just the right time.
It takes such a high degree of skill it's surprising anyone can do it.
If the batter gets everything right, he gives the ball an almighty clout. The ball spends about 1 millisecond in contact with the bat, and when it comes off it might be doing 100km/h.
That's a huge amount of acceleration in a short time, and even though the cricket ball is hard, it deforms considerably.
Now the ball is in flight again, and the same physics apply. In a vacuum it would fly in a perfect parabola, but in the air, it slows. By the time it lands in the stands, it's lost horizontal velocity.
Vertical velocity is less affected, and depends on how high the ball goes. At its peak, vertical velocity is zero, and then accelerates downwards due to gravity.
To make it more complicated, the flight is affected by wind, and if the ball is spinning, aerodynamics will make it swerve. Whether it goes up, down, left, or right depends on the seam and the direction of the spin.
Response by: Rod Taylor, Fuzzy Logic
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