## Uncertainty of speed

$\Delta p \Delta x\geq \frac{h}{4\pi }$

Luyan Zhang - 2D
Posts: 103
Joined: Sat Jul 20, 2019 12:16 am

### Uncertainty of speed

In the practice problem, 1B.27, it states that the velocity of the bowling ball is 5.00 +/- 5.0ms-1,
does this mean that the uncertainty of the velocity is 10m/s because of the plus or minus sign?

LNgo 1G
Posts: 100
Joined: Sat Aug 24, 2019 12:16 am

### Re: Uncertainty of speed

I believe the uncertainty would be 5.0. The plus and minus signs just mean that the variation can go either direction.

Ariel Davydov 1C
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### Re: Uncertainty of speed

Yes, this is exactly what it means, because that is the range in which the speed could potentially fall into.

Luyan Zhang - 2D
Posts: 103
Joined: Sat Jul 20, 2019 12:16 am

### Re: Uncertainty of speed

LNgo 14A wrote:I believe the uncertainty would be 5.0. The plus and minus signs just mean that the variation can go either direction.

But in the worked example in the textbook, the velocity is plus or minus 1m/s, but in the solution for it, it used 2m/s as the uncertainty for speed

KDang_1D
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### Re: Uncertainty of speed

You are correct, the uncertainty would be 2(5 m/s) = 10 m/s.

In his video module, Dr. Lavelle explains that uncertainty should be described as the range. He emphasizes that the uncertainty for +/- 1 would be 2. Additionally, in the problem during lecture that assumes electrons are confined to the nucleus, the uncertainty ($\Delta x$) is the diameter of the nucleus, not the radius.

KDang_1D
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### Re: Uncertainty of speed

Hmm... the solution manual says that it is actually $\Delta v=5.0 ms^{-1}$. I'm not sure why