L****n
发帖数: 12932 | 1 假设某wsn在底线3呎高击球， 在网（3呎)高一呎处过网， 正好落对方底线。 另一个
pro在底线4呎高处平击球， 过网后也落在对方底线， 请问这两个球速相差多少。 |
K****D
发帖数: 30533 | 2 Too many unknown parameters.
Spin/no spin? What spin? How much spin?
What is 平击球? What is pro's net clearance?
【在 L****n 的大作中提到】
: 假设某wsn在底线3呎高击球， 在网（3呎)高一呎处过网， 正好落对方底线。 另一个
: pro在底线4呎高处平击球， 过网后也落在对方底线， 请问这两个球速相差多少。
|
Q*****i
发帖数: 1126 | |
L****n
发帖数: 12932 | 4 文科生？ u got all you need to know in the question. well, if you insist,
the ball top spin at 1000rpm. :-D
【在 K****D 的大作中提到】
: Too many unknown parameters.
: Spin/no spin? What spin? How much spin?
: What is 平击球? What is pro's net clearance?
|
L****n
发帖数: 12932 | 5 let's assume what you said is true. if that helps.
【在 Q*****i 的大作中提到】
: WSN用的是没毛的球
: Pro用的是新球。
|
L****n
发帖数: 12932 | 6 if you want to know more, wsn using a 神拍， pro using a $20 walmart
children racket. hehe. |
w**w
发帖数: 5391 | 7 不考虑空气阻力就中学生了吧。
【在 L****n 的大作中提到】
: 假设某wsn在底线3呎高击球， 在网（3呎)高一呎处过网， 正好落对方底线。 另一个
: pro在底线4呎高处平击球， 过网后也落在对方底线， 请问这两个球速相差多少。
|
L****n
发帖数: 12932 | 8 靠， 这么说真空里面做实验的都小学没毕业乐？
【在 w**w 的大作中提到】
: 不考虑空气阻力就中学生了吧。
|
Q*****i
发帖数: 1126 | 9 咱WSN能打 2/sqrt(5) = 0.8944的速度也不错。 9成pro的功力了 |
L****n
发帖数: 12932 | 10 ?
咱WSN能打 2/sqrt(5) = 0.8944的速度也不错。 9成pro的功力了
★ Sent from iPhone App: iReader Mitbbs 6.88 - iPhone Lite
【在 Q*****i 的大作中提到】
: 咱WSN能打 2/sqrt(5) = 0.8944的速度也不错。 9成pro的功力了
|
|
|
h****a
发帖数: 229 | 11 V1=39(ft)/Sqrt(6(ft)/g)
V2=39(ft)/Sqrt(8(ft)/g)
g=32.2 ft/s^2
V1= 85.8 Km/h
V2= 99 km/h
【在 L****n 的大作中提到】
: 假设某wsn在底线3呎高击球， 在网（3呎)高一呎处过网， 正好落对方底线。 另一个
: pro在底线4呎高处平击球， 过网后也落在对方底线， 请问这两个球速相差多少。
|
b**********s
发帖数: 9531 | |
L****n
发帖数: 12932 | 13 这个有点谱， but I didn't see why u use 6ft for V1, 8ft for V2?
V1=39(ft)/Sqrt(6(ft)/g)V2=39(ft)/Sqrt(8(ft)/g)g=32.2 ft/s^2V1= 85.8 Km/hV2=
99 km/h
★ Sent from iPhone App: iReader Mitbbs 6.88 - iPhone Lite
【在 h****a 的大作中提到】
: V1=39(ft)/Sqrt(6(ft)/g)
: V2=39(ft)/Sqrt(8(ft)/g)
: g=32.2 ft/s^2
: V1= 85.8 Km/h
: V2= 99 km/h
|
h****a
发帖数: 229 | 14 h=1/2*g*t^2
t= sqrt(2h/g)
Km/hV2=
【在 L****n 的大作中提到】
: 这个有点谱， but I didn't see why u use 6ft for V1, 8ft for V2?
:
: V1=39(ft)/Sqrt(6(ft)/g)V2=39(ft)/Sqrt(8(ft)/g)g=32.2 ft/s^2V1= 85.8 Km/hV2=
: 99 km/h
: ★ Sent from iPhone App: iReader Mitbbs 6.88 - iPhone Lite
|
h****a
发帖数: 229 | 15 typo, need to switch 6ft and 8ft
【在 h****a 的大作中提到】
: h=1/2*g*t^2
: t= sqrt(2h/g)
:
: Km/hV2=
|
L****n
发帖数: 12932 | 16 Lets get the answer into something make sense to people, MPH.
★ Sent from iPhone App: iReader Mitbbs 6.88 - iPhone Lite |
t******g
发帖数: 2253 | |
K****D
发帖数: 30533 | 18 No wonder you said all conditional are known. Without air, spin has no
meaning.
【在 L****n 的大作中提到】
: 靠， 这么说真空里面做实验的都小学没毕业乐？
|
L****n
发帖数: 12932 | 19 Glad u realize that. Now, can u answer the question? Or u just have more
question on the question?:-D
No wonder you said all conditional are known. Without air, spin has
nomeaning.
★ Sent from iPhone App: iReader Mitbbs 6.88 - iPhone Lite
【在 K****D 的大作中提到】
: No wonder you said all conditional are known. Without air, spin has no
: meaning.
|
w**w
发帖数: 5391 | 20 107 mph
80 mph
想不起来公式了，只好用抛物线凑了。 |
|
|
w******n
发帖数: 13172 | 21 一看就是文科生出的题。球的spin产生的涡流是非常复杂的，而且空气阻力对球飞行线
路影响非常大。你非要说“假设在空气稀薄无风处， 空气阻力不计。”这基本就是把
最重要的因素给排除了，根本没有任何实际意义。还有球本身的硬度和变形程度对结果
的有很大影响。要不每次世界杯（足球），阿迪达斯都要出个新球。不同的足球在空中
的飞行线路、速度、旋转都完全不一样 |
a***8
发帖数: 2433 | 22 The answer will cost you 100 mit$$$, will you? |
L****n
发帖数: 12932 | 23
sure, put your calculation process out in detail.
If you are wrong, you owe me 100weibi, yeah? If you are correct(just final
results), i'll pay you 100wb.
【在 a***8 的大作中提到】
: The answer will cost you 100 mit$$$, will you?
|
L****n
发帖数: 12932 | 24 文科生出的题都把码工们考倒了， wsn们颜面无存啊。 呵呵。 不是小瞧尼玛， 空气
阻力加进去， 怕你脑筋转不过来。 就这个简化的，so far没一个全答对的。 有部分
答对的。
【在 w******n 的大作中提到】
: 一看就是文科生出的题。球的spin产生的涡流是非常复杂的，而且空气阻力对球飞行线
: 路影响非常大。你非要说“假设在空气稀薄无风处， 空气阻力不计。”这基本就是把
: 最重要的因素给排除了，根本没有任何实际意义。还有球本身的硬度和变形程度对结果
: 的有很大影响。要不每次世界杯（足球），阿迪达斯都要出个新球。不同的足球在空中
: 的飞行线路、速度、旋转都完全不一样
|
K****D
发帖数: 30533 | 25 实际上，考虑了空气阻力要容易一些。
http://twu.tennis-warehouse.com/cgi-bin/trajectory_maker.cgi#ou
根据spin的不同，可以有很多种组合，偶只列了一种偶认为还算合理的。
WSN和pro都假设是在击打静止的球。
【在 L****n 的大作中提到】
: 文科生出的题都把码工们考倒了， wsn们颜面无存啊。 呵呵。 不是小瞧尼玛， 空气
: 阻力加进去， 怕你脑筋转不过来。 就这个简化的，so far没一个全答对的。 有部分
: 答对的。
|
a***8
发帖数: 2433 | 26 1. 67.8mph
2. 106.4mph
1.
y = -16.1 * t^2 + 8.85 * t + 3 --- t is time
x = 99 * t
Unit is feet, second
Total travel time is 0.8 second
initial speed x = 99 ft/s, y = 8.85 ft/s, net speed = 99.4 ft/s
initial shot angle = 5.1 degree
2.
y = -16.1 * t^2 + 4
x = 156 * t
total travel time is: 0.5 second
initial speed x = 156 ft/s, y = 0 ft/s net speed = 156 ft/s
ball fly over net with a hair clearance
This is high school physics and equation solving, doesn't meter if your
are
a 文科生 or 理科wsn, you should be able to get it. |
L****n
发帖数: 12932 | 27 start to make some sense. tell me how you get this, i assume you mean x-
speed on the horizontal plan, y-speed on the vertical plane. |
L**F
发帖数: 615 | 28 看似简单，其实还是要绕个弯的：
（1）网球落地所用时间。 对于平击，h=1/2gt^2 h=4ft t=0.5s; 对于wsn击球，分成
球上升和下降两个部分, h1=1ft, h2=4ft t=t1+t2=0.75s
(2) 球的水平速度。 网球场长度 l=78ft. 对于平击 v=156ft/s=106mph; 对于wsn击球
，v=104ft/s=71mph.
(3) 球的垂直速度。根据能量守恒。 对于平击和wsn击球，mgh=1/2mv^2，h=4ft v=4.
9m/s=11mph.
(4) 矢量相加，对于平击 v=107mph, 对于wsn击球，v=72mph.【 在 Lexian (蒙古大夫
) 的大作中提到: 】 |
a***8
发帖数: 2433 | 29 no, x, y are coordination of positions. x', y' are speed, x", y" are
acceleration. x is horizontal with 0 at one baseline, and y is vertical with
0 at ground surface. |
L****n
发帖数: 12932 | 30 这个和俺30年前某某表物理竞赛的回答是一样的， unfortunately, it was WRONG.
close, but wrong.
【在 L**F 的大作中提到】
: 看似简单，其实还是要绕个弯的：
: （1）网球落地所用时间。 对于平击，h=1/2gt^2 h=4ft t=0.5s; 对于wsn击球，分成
: 球上升和下降两个部分, h1=1ft, h2=4ft t=t1+t2=0.75s
: (2) 球的水平速度。 网球场长度 l=78ft. 对于平击 v=156ft/s=106mph; 对于wsn击球
: ，v=104ft/s=71mph.
: (3) 球的垂直速度。根据能量守恒。 对于平击和wsn击球，mgh=1/2mv^2，h=4ft v=4.
: 9m/s=11mph.
: (4) 矢量相加，对于平击 v=107mph, 对于wsn击球，v=72mph.【 在 Lexian (蒙古大夫
: ) 的大作中提到: 】
|
|
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w**w
发帖数: 5391 | 31 107和84，不对吗？主要就是烦，加上换单位。
测速,都是X方向的，没有什么Y方向的事吧。
【在 L****n 的大作中提到】
: 这个和俺30年前某某表物理竞赛的回答是一样的， unfortunately, it was WRONG.
: close, but wrong.
|
w**w
发帖数: 5391 | 32 这个不对。更繁琐些。
【在 L**F 的大作中提到】
: 看似简单，其实还是要绕个弯的：
: （1）网球落地所用时间。 对于平击，h=1/2gt^2 h=4ft t=0.5s; 对于wsn击球，分成
: 球上升和下降两个部分, h1=1ft, h2=4ft t=t1+t2=0.75s
: (2) 球的水平速度。 网球场长度 l=78ft. 对于平击 v=156ft/s=106mph; 对于wsn击球
: ，v=104ft/s=71mph.
: (3) 球的垂直速度。根据能量守恒。 对于平击和wsn击球，mgh=1/2mv^2，h=4ft v=4.
: 9m/s=11mph.
: (4) 矢量相加，对于平击 v=107mph, 对于wsn击球，v=72mph.【 在 Lexian (蒙古大夫
: ) 的大作中提到: 】
|
a***8
发帖数: 2433 | 33 no, x, y are coordination of positions. x', y' are speed, x", y" are
acceleration. x is horizontal with 0 at one baseline, and y is vertical with
0 at ground surface. |
a***8
发帖数: 2433 | 34 for wsn 击球, 4ft is not the peak, that's why you are wrong.
【在 L**F 的大作中提到】
: 看似简单，其实还是要绕个弯的：
: （1）网球落地所用时间。 对于平击，h=1/2gt^2 h=4ft t=0.5s; 对于wsn击球，分成
: 球上升和下降两个部分, h1=1ft, h2=4ft t=t1+t2=0.75s
: (2) 球的水平速度。 网球场长度 l=78ft. 对于平击 v=156ft/s=106mph; 对于wsn击球
: ，v=104ft/s=71mph.
: (3) 球的垂直速度。根据能量守恒。 对于平击和wsn击球，mgh=1/2mv^2，h=4ft v=4.
: 9m/s=11mph.
: (4) 矢量相加，对于平击 v=107mph, 对于wsn击球，v=72mph.【 在 Lexian (蒙古大夫
: ) 的大作中提到: 】
|
w**w
发帖数: 5391 | 35 你的第一个解法,看不懂。你怎么知道角度的？我算了一下，到27.3'才最高点。
with
【在 a***8 的大作中提到】
: no, x, y are coordination of positions. x', y' are speed, x", y" are
: acceleration. x is horizontal with 0 at one baseline, and y is vertical with
: 0 at ground surface.
|
a***8
发帖数: 2433 | |
w**w
发帖数: 5391 | 37 第二好象应该是0。788秒，67，68MPH。
【在 w**w 的大作中提到】
: 107和84，不对吗？主要就是烦，加上换单位。
: 测速,都是X方向的，没有什么Y方向的事吧。
|
L****n
发帖数: 12932 | 38 you have to put your answer out in detail, how to get to that equation?
i do think you may have the right answer, but i need to see it.
【在 a***8 的大作中提到】
: 蒙古大夫, my baozi please.
|
a***8
发帖数: 2433 | 39 yes, y peaks at 4.2ft when travels 27ft into the court, 12ft from the
net.
angle is arctg(y'/x') @ t=0 ya...
【在 w**w 的大作中提到】
: 你的第一个解法,看不懂。你怎么知道角度的？我算了一下，到27.3'才最高点。
:
: with
|
w******n
发帖数: 13172 | 40 理科wsn能解的只能是没空气的。有空气的现在的理论根本算不清楚，只能风洞试验。
那就是工科wsn干的事了
【在 K****D 的大作中提到】
: No wonder you said all conditional are known. Without air, spin has no
: meaning.
|
|
|
K****D
发帖数: 30533 | 41 工科男的直觉带领偶找到了TW的模拟工具。
工==工具
理==理想化 阿。
【在 w******n 的大作中提到】
: 理科wsn能解的只能是没空气的。有空气的现在的理论根本算不清楚，只能风洞试验。
: 那就是工科wsn干的事了
|
a***8
发帖数: 2433 | 42 true...
【在 w******n 的大作中提到】
: 理科wsn能解的只能是没空气的。有空气的现在的理论根本算不清楚，只能风洞试验。
: 那就是工科wsn干的事了
|
L**F
发帖数: 615 | 43 我的假设是球在网处达到最大高度，如果完全是一条抛物线，情况更复杂一些，
抛物线的方程由3个点确定 （0，3），（39，4），（78，0）， 求出最大高度，
同样方法计算即可。
【在 L****n 的大作中提到】
: 这个和俺30年前某某表物理竞赛的回答是一样的， unfortunately, it was WRONG.
: close, but wrong.
|
L****n
发帖数: 12932 | 44 that's the right way.
【在 L**F 的大作中提到】
: 我的假设是球在网处达到最大高度，如果完全是一条抛物线，情况更复杂一些，
: 抛物线的方程由3个点确定 （0，3），（39，4），（78，0）， 求出最大高度，
: 同样方法计算即可。
|
a***8
发帖数: 2433 | 45 flat shot is easy, ball travel 78ft while free-fall drop 4ft...
for wsn shot, y = a*t^2 + b*t + c
y''=g, --> a = -16.1 (g = -32.2)
y0 = 3 --> c = 3
assume Tn is time to get net, so time to the other baseline is 2*Tn
use y|Tn = 4 (net) and y|2*Tn = 0 (baseline) to find b = 8.85, Tn = 0.4
That's it. Baozi. |
L**F
发帖数: 615 | 46 估算了一下，如果运动轨迹是一条抛物线，球的虽大高度是离地4.225ft. 最大水平速
度为67.4mph. 加上垂直方向上的速度11.4mph,最终速度为 68.4mph.
【在 L****n 的大作中提到】
: that's the right way.
|
L****n
发帖数: 12932 | 47 very good. wb transferred.
【在 a***8 的大作中提到】
: flat shot is easy, ball travel 78ft while free-fall drop 4ft...
: for wsn shot, y = a*t^2 + b*t + c
: y''=g, --> a = -16.1 (g = -32.2)
: y0 = 3 --> c = 3
: assume Tn is time to get net, so time to the other baseline is 2*Tn
: use y|Tn = 4 (net) and y|2*Tn = 0 (baseline) to find b = 8.85, Tn = 0.4
: That's it. Baozi.
|
L****n
发帖数: 12932 | 48 yeah, 最大的弯就是4ft不是最高处。thanks for input.
【在 L**F 的大作中提到】
: 估算了一下，如果运动轨迹是一条抛物线，球的虽大高度是离地4.225ft. 最大水平速
: 度为67.4mph. 加上垂直方向上的速度11.4mph,最终速度为 68.4mph.
|
a***8
发帖数: 2433 | 49 Thx, now I can play some gambling...hehe
【在 L****n 的大作中提到】
: very good. wb transferred.
|
L****n
发帖数: 12932 | 50 你是正牌理科wsn, 其它都是伪的。 呵呵。
【在 a***8 的大作中提到】
: Thx, now I can play some gambling...hehe
|
|
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b**********s
发帖数: 9531 | 51 dude, i don't think you even get the right answer.
this problem is actually a 3D geometry question. so both wsn and pro ball
speed has a range, and in some case, wsn may hit faster than pro.
【在 L****n 的大作中提到】
: yeah, 最大的弯就是4ft不是最高处。thanks for input.
|
L****n
发帖数: 12932 | 52 yeah, if you start thinking of lateral movement, like aakk did. there might
be a possibility. and then add in air density, ball felt, spin factor...
this will be a question with no answer. 那就真成了理论派了。
my point is, just move up you strike zone by 1 ft, it allows you to hit the
ball almost 60% faster. everything else been equal. and it explains why the
top player are all nearly 6'1", 6'2" tall, their natural strike zone is
about 4ft. high. bigger body than that, your speed would suffer.
【在 b**********s 的大作中提到】
: dude, i don't think you even get the right answer.
: this problem is actually a 3D geometry question. so both wsn and pro ball
: speed has a range, and in some case, wsn may hit faster than pro.
|
d******x
发帖数: 11837 | 53 同学，1ft好长一大截了。。。
might
the
the
【在 L****n 的大作中提到】
: yeah, if you start thinking of lateral movement, like aakk did. there might
: be a possibility. and then add in air density, ball felt, spin factor...
: this will be a question with no answer. 那就真成了理论派了。
: my point is, just move up you strike zone by 1 ft, it allows you to hit the
: ball almost 60% faster. everything else been equal. and it explains why the
: top player are all nearly 6'1", 6'2" tall, their natural strike zone is
: about 4ft. high. bigger body than that, your speed would suffer.
|
L****n
发帖数: 12932 | 54 well, your shoulder/elbow position is relatively fixed (extend of ankle at
every strike can lift couple inches), forearm is about 1.5 ft, plus racket
length, close to 4 feet, closing of elbow a little can achieve move the
strike zone up a foot. the difficult part is catch the ball near the top.
much faster timing and foot work is needed.
【在 d******x 的大作中提到】
: 同学，1ft好长一大截了。。。
:
: might
: the
: the
|
w**w
发帖数: 5391 | 55 高中的时候做这类题，都是砍瓜切菜一般。
【在 L****n 的大作中提到】
: 你是正牌理科wsn, 其它都是伪的。 呵呵。
|
K****D
发帖数: 30533 | 56 No, the answer to your question doesn't have any significant
point.
不要从理想化、简化模型的结果进行推论。Any 推论 can be dangerously
misleading.
引用aakk123的名言："前提不对，推导再严密也白搭。"
might
the
the
【在 L****n 的大作中提到】
: yeah, if you start thinking of lateral movement, like aakk did. there might
: be a possibility. and then add in air density, ball felt, spin factor...
: this will be a question with no answer. 那就真成了理论派了。
: my point is, just move up you strike zone by 1 ft, it allows you to hit the
: ball almost 60% faster. everything else been equal. and it explains why the
: top player are all nearly 6'1", 6'2" tall, their natural strike zone is
: about 4ft. high. bigger body than that, your speed would suffer.
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L****n
发帖数: 12932 | 57 Hehe, i have to say your answer(s) were kinda clueless among all.
No, the answer to your question doesn't have any significantpoint.不要从理想
化、简化模型的结果进行推论。Any........
★ Sent from iPhone App: iReader Mitbbs 6.88 - iPhone Lite
【在 K****D 的大作中提到】
: No, the answer to your question doesn't have any significant
: point.
: 不要从理想化、简化模型的结果进行推论。Any 推论 can be dangerously
: misleading.
: 引用aakk123的名言："前提不对，推导再严密也白搭。"
:
: might
: the
: the
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K****D
发帖数: 30533 | 58 Of course, I wouldn't even start analyzing these kinds of problems
on paper. The condition that "there is no air" already hammered
95% of the motivation of a typical 工科男 down...
My first instinct is how to place cameras and measure the speeds
instead of getting out scratch paper for equations...
【在 L****n 的大作中提到】
: Hehe, i have to say your answer(s) were kinda clueless among all.
:
: No, the answer to your question doesn't have any significantpoint.不要从理想
: 化、简化模型的结果进行推论。Any........
: ★ Sent from iPhone App: iReader Mitbbs 6.88 - iPhone Lite
|
K****D
发帖数: 30533 | 59 Some further explanation why this question discourages me:
1) No air == not applicable to reality.
2) Because of 1, topspin does not help with net clearance. You
obviously expected the pro to hit a ball that kisses the
net at 3 ft -- again a highly impractical situation. (I added
1000rpm to the pro's ball contact in my simulation, so you saw
some net clearance.)
Because of 1-2, I felt the answer to this question has very little
meaning to every day life and I couldn't draw any conclusion out
of it. Thus I was discouraged to spend time on it.
【在 K****D 的大作中提到】
: Of course, I wouldn't even start analyzing these kinds of problems
: on paper. The condition that "there is no air" already hammered
: 95% of the motivation of a typical 工科男 down...
: My first instinct is how to place cameras and measure the speeds
: instead of getting out scratch paper for equations...
|
L****n
发帖数: 12932 | 60 base on the same logic, i have to say your speed gun and wind tunnel measure
will have no use in reality as well, because wind never blow the same way,
balls are never exactly the same, spin could be gazillion different way,
hell, even air density is not the same, btw, did it even come to your mind
that air humidity and viscosity play a factor in how the ball will fly? so
please don't act like you are able to solve the problem once you put the "
reality" into the equation. You haven't demonstrated you even know how to
get the answer in the simplest form.
just a reminder, even you beloved radar gun is manufactured based on some "
theory" and omit out many factors the could make it not "realistic".
【在 K****D 的大作中提到】
: Some further explanation why this question discourages me:
: 1) No air == not applicable to reality.
: 2) Because of 1, topspin does not help with net clearance. You
: obviously expected the pro to hit a ball that kisses the
: net at 3 ft -- again a highly impractical situation. (I added
: 1000rpm to the pro's ball contact in my simulation, so you saw
: some net clearance.)
: Because of 1-2, I felt the answer to this question has very little
: meaning to every day life and I couldn't draw any conclusion out
: of it. Thus I was discouraged to spend time on it.
|
|
|
K****D
发帖数: 30533 | 61 The major difference between the mindsets of a scientist and an engineer
is that scientists would argue on some theoretical details because
theories have to be perfect and sound; while an engineer would ignore
sth that would cause some 5% error.
To me, dwelling on the details of a theoretical flaw that
could cause 5mph error, while the whole theory is built on the basis
of "no air", is completely missing the point. It may have scientific
significance but has very little engineering sense.
Of course every engineering piece is based on certain theories. However,
since the theory behind radar guns guarantees them to be as accurate
as +/- 5mph (or whatever number they claim), I would trust them much
more than any theoretical deduction on paper. The fact that ball speeds
are mesured by radar guns at tournaments instead of by the geometry
computation of mathmeticians proves such similar reasoning by the
tournament organizers.
measure
,
【在 L****n 的大作中提到】
: base on the same logic, i have to say your speed gun and wind tunnel measure
: will have no use in reality as well, because wind never blow the same way,
: balls are never exactly the same, spin could be gazillion different way,
: hell, even air density is not the same, btw, did it even come to your mind
: that air humidity and viscosity play a factor in how the ball will fly? so
: please don't act like you are able to solve the problem once you put the "
: reality" into the equation. You haven't demonstrated you even know how to
: get the answer in the simplest form.
: just a reminder, even you beloved radar gun is manufactured based on some "
: theory" and omit out many factors the could make it not "realistic".
|
L****n
发帖数: 12932 | 62 忙了24小时， let's cont the topic.
now that you give yourself 5% margin of error, we can add air into the
scenario.
the exact same question, but they now play at sea level. the difference in
speed, ratio of Vwsn/Vpro, (we have to use average horizontal speed because
it's now it decelerates) is within 5% of the original, surprised?
【在 K****D 的大作中提到】
: The major difference between the mindsets of a scientist and an engineer
: is that scientists would argue on some theoretical details because
: theories have to be perfect and sound; while an engineer would ignore
: sth that would cause some 5% error.
: To me, dwelling on the details of a theoretical flaw that
: could cause 5mph error, while the whole theory is built on the basis
: of "no air", is completely missing the point. It may have scientific
: significance but has very little engineering sense.
: Of course every engineering piece is based on certain theories. However,
: since the theory behind radar guns guarantees them to be as accurate
|
L****n
发帖数: 12932 | 63 if u want to consider spin, let's said wan able to spin the ball exactly the
same as the pro.
【在 L****n 的大作中提到】
: 忙了24小时， let's cont the topic.
: now that you give yourself 5% margin of error, we can add air into the
: scenario.
: the exact same question, but they now play at sea level. the difference in
: speed, ratio of Vwsn/Vpro, (we have to use average horizontal speed because
: it's now it decelerates) is within 5% of the original, surprised?
|
a****7
发帖数: 295 | 64 Why court width is ignored?
If you hit cross court with same time, your ball speed is much faster.
【在 a***8 的大作中提到】
: flat shot is easy, ball travel 78ft while free-fall drop 4ft...
: for wsn shot, y = a*t^2 + b*t + c
: y''=g, --> a = -16.1 (g = -32.2)
: y0 = 3 --> c = 3
: assume Tn is time to get net, so time to the other baseline is 2*Tn
: use y|Tn = 4 (net) and y|2*Tn = 0 (baseline) to find b = 8.85, Tn = 0.4
: That's it. Baozi.
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K****D
发帖数: 30533 | 65 Before we continue, I just have one question:
In your original question, why you require a wsn to clear the net by
1 ft, while the pro can clear the net by 0 ft?
A more reasonable setup should be both of them clear the net by 1 ft.
Even at theoretical level, we need to compare apple to apple, no?
I would expect hitting at higher height is faster, but +60%, no.
This is not a 5% error...
because
【在 L****n 的大作中提到】
: 忙了24小时， let's cont the topic.
: now that you give yourself 5% margin of error, we can add air into the
: scenario.
: the exact same question, but they now play at sea level. the difference in
: speed, ratio of Vwsn/Vpro, (we have to use average horizontal speed because
: it's now it decelerates) is within 5% of the original, surprised?
|
L****n
发帖数: 12932 | 66 i didn't design the question, i just remember the question, from many years
ago. I'd guess the the question was designed this way so people wouldn't
realize immediately the max high of wsn shot is not 4ft.
【在 K****D 的大作中提到】
: Before we continue, I just have one question:
: In your original question, why you require a wsn to clear the net by
: 1 ft, while the pro can clear the net by 0 ft?
: A more reasonable setup should be both of them clear the net by 1 ft.
: Even at theoretical level, we need to compare apple to apple, no?
: I would expect hitting at higher height is faster, but +60%, no.
: This is not a 5% error...
:
: because
|
K****D
发帖数: 30533 | 67 Ok, so that is a good question to train 理科思维缜密性。But would I
draw conclusions from the results? Probably not.
I think the results from TW's simulation (95mph vs 78mph) sounds more
reasonable as both of the curves clear the net by about 1 ft. I don't
know how they calculated, but probably they used some 经验公式。
(I let wsn to hit witn 2000rpm spin while the pro to hit with 1000rpm.
Basically the wsn hits a moderate topspin while the pro hits a flat ball.)
years
【在 L****n 的大作中提到】
: i didn't design the question, i just remember the question, from many years
: ago. I'd guess the the question was designed this way so people wouldn't
: realize immediately the max high of wsn shot is not 4ft.
|
a***8
发帖数: 2433 | 68 The major difference:
"Scientists discover the world that exists; engineers create the world that
never was." - Theodore Von Karman
【在 K****D 的大作中提到】
: The major difference between the mindsets of a scientist and an engineer
: is that scientists would argue on some theoretical details because
: theories have to be perfect and sound; while an engineer would ignore
: sth that would cause some 5% error.
: To me, dwelling on the details of a theoretical flaw that
: could cause 5mph error, while the whole theory is built on the basis
: of "no air", is completely missing the point. It may have scientific
: significance but has very little engineering sense.
: Of course every engineering piece is based on certain theories. However,
: since the theory behind radar guns guarantees them to be as accurate
|
