Help me solve an argument I had with a collegaue.
Speed is simply distance over time, hence a scalar. Velocity is rate of change of position over time. (half remembered school physics classes).
A ball delivered to a batman by a bowler will have both a horizontal and vertical velocity component. Most speed guns measure simply measure horizontal velocity and ignore the vertical bit.
Now my argument is that since the vast majority of deliveries bounce on the way to the batsman, the speed gun reading which comes up, is misleading. At least as to how fast the batter percieves the ball. This is epecially true of balls with high bounce. Which is why sometimes batsmen seem to have no problem with a 95mph fast ball, while seem to be totally out of sorts with an 85 mph ball which bounces high.
He says its bollocks
(This is based on sports, but is about physics so, I think this is the righ forum).
*I am guessing this is also the case in baseball, though less so due to the fact that the ball is thrown on the full.
A lot is to do with the height of the bowler of course. Joel Garner had a legendary yorker and the height it came down from was probably disconcerting, and as you would expect his bouncers were pretty lethal too.
I’m pretty sure the speed gun only measures the speed at the moment is leaves the bowler’s hand. Regardless of the angle of release, I assume the vertical difference in deliveries leaving the hand isn’t significant. Even pitched baseballs, which are a lot faster and rarely hit the ground first, have slowed to the 80’s by the time they reach the batter.
There’s a couple of different things in the question.
First, on the physics end: yes, the radar gun will generally not get the vertical component of velocity, but that’s very small compared to the horizontal component, so in the end the speed is pretty close.
But, it’s quite possible that a lot of vertical movement makes a ball seem faster to the batsman. This isn’t about physics but about human physiology and perception.
It’s not bollocks, you are correct. Radar guns (I.e. the guns used in cricket to display speed instantly) are line of sight measurement devices and measure speed only in the line of sight. Here’s a published paper : https://iopscience.iop.org/article/10.1088/0031-8949/91/2/023008
But there are multiple high speed high resolution cameras deployed in the stadium that can compute the true velocity and trajectory in 3-D. Commonly this system is used to predict LBWs.
This deals with baseball, but the principle is similar.
In the past, pitch velocities were measured with a radar gun, which took some time to pick up the ball and measure the speed. The velocity was that of the ball about 2/3 of the way along its path.
Currently speeds are measured with a laser gun which picks up the ball as soon as it leaves the pitcher’s hand. The same pitch ‘reads’ faster now, since aerodynamic drag hasn’t slowed the ball.
I would imaging that a bouncing ball would be slowed even more by contact with the ground. If it’s harder to hit (I admit I don’t understand Crickett) it may be due to factors other than speed.
Hitting a cricket ball hurled down a 22yard wicket by a fast bowler is pretty much an act of faith. You only really see it as it leaves the bowler’s hand and you have to make a judgement as to where it will be in half a second or so. Now just as with baseball, the ball moves sideways in the air and cricket balls have a seam which helps. Add in the contact with the ground, which is nominally grass, but it is mowed right down to the ground and may have scrapes and dints from people running on it and the scores of previous balls that hit the same spot. The bowler might also have put a spin on the ball so that it flies off sideways just like a pool ball with ‘English’ on it.
As well as deciding where it will be, you have to decide how to deal with it. Unlike baseball, the batsman or woman can steer the ball in any direction they choose. A slight glance to avoid the wicketkeeper and off it goes to the boundary for four; a solid whack with the middle of the bat and it flies over the boundary for six; stopping it dead with a loose bat frustrates the bowler but scores nothing. Of course - time it wrong and that little red ball goes up in the air to be caught by people who are cunningly placed for just that eventuality and you are on the long walk back to the pavilion, playing the stroke over in your head and wondering what the hell happened.
I think speed is only one component of the equation. Having played cricket a bit (and have the scars to prove it), the most unsettling delivery is the one that bounces on you because your reaction has to account for the amount of bounce that may be unpredictable (nature of pitch, height of delivery etc). This means you are worried about it crashing into your upper body area if miss the hitting it or mistime your sway back to avoid the ball. So, you have far less time to judge where the ball is going to be when it reaches you.
Its the same thing when spinners operate. Many batsmen try to read the ball off the pitch, which gives them way less time to react than off the hand.
I agree with you. The ball has significant movement in three dimensions and the direction the ball is moving after the bounce may be significantly different from the direction it was moving before the bounce. The human eye is very good at tracking 2D movement, but not so good at tracking 3D movement.
I don’t believe that the batsman’s eye/brain can possibly track the ball. They make a judgement when they see how the bowler releases the ball and the way his arm moves; then they make the stroke accordingly. Note that they will have started their move at the same time as the ball leaves the hand. A top-level batsman on form will get it right pretty often; the rest of us will miss the ball completely.
To put some numbers on this, a pitch of 150 km/hr (about 95 mph) is a little over 40 meters/sec. So it covers the distance wicket to wicket in about half a second. In that time, gravity will accelerate the ball downward to a final vertical velocity of under 5 m/s. [Yeah, it doesn’t happen exactly this way, but this is a good quick estimate of the size of the numbers involved].
At a horizontal velocity of 40 m/s and vertical of 5 m/s, a horizontally-oriented speed gun will read 40 m/s while the actual overall speed is 40.3 m/s. So I think we can agree that the speed guns give a pretty good reading, even if they ignore vertical components.
Again, human perception is not at all so simple and it’s possible (and I think likely) that balls with lots of vertical movement feel faster to bowlers.
Cricket’s not like that. The ball moves slower, but you only really know where it’s going after the bounce. You can make a judgement based on what kind of balls the bowler is likely to pitch, but watching the bowler is much less important than it is in baseball.
I’ve been watching a lot of cricket lately, and there appears to be at least some importance on bowlers disguising their deliveries so as not to ‘tip’ the batsman. Also, in some of the interview shows with bowlers, I’ve heard comments about how well they hide the ball in their hand prior to the toss. So it must come into play at some of the higher levels of cricket.
With a straight-down-the-middle fastball, all you have to worry about is when to swing (which is already tough enough; I could never do it, but the pros seem to manage it OK). But if the ball has a significant motion in some other component, then you have to worry both about when to swing and where. It’s easy to see why that would make it harder to hit.
So a rising or dipping ball, at 85, will feel faster than at flat trajectory one at 90? As will a swinging one.
No wonder in swinging Yorker is so difficult to play.
Wouldn’t acceleration due to gravity be an issue in calculating vertical velocity?
In principle, yes, but that acceleration doesn’t add up to much in the brief time that the ball is in the air, and what little it does add up to, the batter is used to it and expecting it.
This article is very dense and I didn’t really follow it all, but it suggests that a baseball fielder may be able to get the ball to another fielder slightly faster on the hop than in the air, so it may be that a bowled cricket ball actually can pick up speed, especially because bowling is a more controlled motion than a throw made by a fielder in the heat of the action.