Finding the angle between a plumb line and the Earth's surface.

In summary, the conversation discusses the use of Newton's second law to find the angle between a plumb line hanging freely over the Earth's pole and one hanging over the surface of the Earth. The equation ##\theta = arctan(\frac{v\omega}{g})## is used, with ##r = \frac{v}{w}## and ##a = r\omega^{2}##. The final result is ##\theta = 1.65 \times 10^{-3}## radians, which is close to the book's answer of ##\theta = 5.25 \times 10^{-4}## radians, but the book's calculation left out the value of pi.
  • #1
andyonassis
4
1
Homework Statement
A plane flies across the north pole at 223.52 m/s, following a meridian of longitude (which rotates around the earth). Find the angle between the direction of a plumb line hanging freely as it passes over the pole and one hanging freely at the surface of the earth over the pole.
Relevant Equations
F = ma
$$\omega = \frac{2\pi}{T} $$
From Newton's second law:
$$T_{x} = F_{turn}$$
So
$$T \sin \theta = ma$$
$$T_{y} = F_{y}$$
so
$$T \cos \theta = mg$$
Equate the two equations to get:
$$ \frac{T \sin \theta}{a} = \frac{T \cos \alpha}{g} $$
and the angle is given by:
$$tan (\theta) = \frac{a}{g} $$
where ##r = \frac{v}{w}## and ##a = r\omega^{2}##
From this we get:
$$\theta = arctan(\frac{v\omega}{g}) = arctan(\frac{223.52}{9.8} \times \frac{2\pi}{24\times 60 \times 60}) = 1.65 \times 10^{-3} radians$$

However, the book says ##\omega = 2.31 \times 10^-4 rad/s## so ##\theta = 5.25 \times 10^{-4}##radians.
 
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  • #2
andyonassis said:
Homework Statement:: A plane flies across the north pole at 223.52 m/s, following a meridian of longitude (which rotates around the earth). Find the angle between the direction of a plumb line hanging freely as it passes over the pole and one hanging freely at the surface of the Earth over the pole.
Relevant Equations:: F = ma
$$\omega = \frac{2\pi}{T} $$

From Newton's second law:
$$T_{x} = F_{turn}$$
So
$$T \sin \theta = ma$$
$$T_{y} = F_{y}$$
so
$$T \cos \theta = mg$$
Equate the two equations to get:
$$ \frac{T \sin \theta}{a} = \frac{T \cos \alpha}{g} $$
and the angle is given by:
$$tan (\theta) = \frac{a}{g} $$
where ##r = \frac{v}{w}## and ##a = r\omega^{2}##
From this we get:
$$\theta = arctan(\frac{v\omega}{g}) = arctan(\frac{223.52}{9.8} \times \frac{2\pi}{24\times 60 \times 60}) = 1.65 \times 10^{-3} radians$$

However, the book says ##\omega = 2.31 \times 10^{-5}## rad/s so ##\theta = 5.25 \times 10^{-4}##radians.
Whoever did the calculation for the book left out π.
 
  • #3
haruspex said:
Whoever did the calculation for the book left out π.
so my answer isn't technically wrong?
 
  • #4
andyonassis said:
so my answer isn't technically wrong?
Your answer looks right to me.
 

1. What is a plumb line?

A plumb line is a tool used by scientists to determine the vertical direction, or the direction of gravity, at a specific location. It consists of a weight attached to a string or cord, which is suspended from a fixed point.

2. How is the angle between a plumb line and the Earth's surface measured?

The angle between a plumb line and the Earth's surface is measured using a device called a plumb bob, which is attached to the bottom of the string. The plumb bob will hang perpendicular to the Earth's surface, and the angle can be measured using a protractor or other angle-measuring tool.

3. What factors can affect the angle between a plumb line and the Earth's surface?

The angle between a plumb line and the Earth's surface can be affected by several factors, including the Earth's rotation, local topography, and the presence of large masses such as mountains or bodies of water.

4. Why is finding the angle between a plumb line and the Earth's surface important?

Knowing the angle between a plumb line and the Earth's surface is important for understanding the Earth's gravitational field and how it varies in different locations. It can also be used to determine the height of objects and to create accurate maps and survey measurements.

5. Can the angle between a plumb line and the Earth's surface change over time?

Yes, the angle between a plumb line and the Earth's surface can change over time due to factors such as tectonic plate movement, changes in the Earth's rotation, and the redistribution of mass within the Earth. However, these changes are typically very small and may not be noticeable without precise measurements.

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