How do I Taylor expand the gravitational field in terms of h/R <<1?

This can be done by writing ##f(x) = \sum_{n=0}^\infty a_n x^n## and finding the coefficients ##a_n##. The first few terms are ##a_0 = 1##, ##a_1 = -2##, ##a_2 = 3##, ##a_3 = -4##, and so on. Substituting this into the original equation for ##\underline{G}(\underline{r})##, we get \underline{G}(\underline{r}) = \frac{-GM}{R^2} \sum_{n=0}^\infty a_n \left(\frac{h}{R}\right)^n \underline
  • #1
spacetimedude
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Homework Statement


Consider the position vector of a mass m at height h above the Earth's surface to be [itex] \underline{r}=(R+h)\underline{e}_z [/itex] where R is the radius of the Earth.
Make a Tylor expansion in h/R <<1 of the gravitational field
[tex] \underline{G}(\underline{r})=\frac{-GM\underline{r}}{r^3}[/tex]
to show that the gravitational force on a mass m can be written as [tex] \underline{F} \approx mg\underline{e}_z[/tex] giving an expression for g in terms of R and M, the mass of the Earth.
Find the first correction (h-dependent) to the gravitational force.

Homework Equations

The Attempt at a Solution


I am having trouble understanding how to expand the function in h/R<<1.

We can rewrite [tex] \underline{G}(\underline{r})=\frac{-GM(R+h)}{(R+h)^3}\underline{e}_z[/tex] which then can then be expressed as [tex]\underline{G}(\underline{r})=\frac{-GM}{R^2}(\frac{h}{R}+1)^{-2}\underline{e}_z[/tex]
I am not sure how to proceed with the expansion.
Any explanation will be appreciated.
 
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  • #2
Let ##x = h/R##. You need to make a Taylor series expansion of the function ##f(x) = (x+1)^{-2}##.
 

FAQ: How do I Taylor expand the gravitational field in terms of h/R <<1?

1. What is a Taylor expansion?

A Taylor expansion is a mathematical technique used to approximate a function with a polynomial series. It allows for the estimation of the value of a function at a specific point by using the function's derivatives at that point.

2. Why is a Taylor expansion useful?

A Taylor expansion can be useful for simplifying complex functions, making them easier to analyze and manipulate. It can also provide an approximation of a function's behavior near a specific point, which can be helpful in solving problems in physics, engineering, and other fields.

3. How is a Taylor expansion calculated?

A Taylor expansion is calculated by taking the derivatives of a function at a specific point, and using those values in a polynomial series. The more terms included in the series, the more accurate the approximation will be.

4. What is the difference between a Taylor expansion and a Maclaurin expansion?

A Taylor expansion is a generalization of a Maclaurin expansion, which is a special case where the point of expansion is at x = 0. In other words, a Maclaurin series is a Taylor series centered at 0.

5. What are some applications of Taylor expansions in real life?

Taylor expansions have numerous applications in many fields, including physics, engineering, economics, and finance. They are used to approximate the behavior of physical systems, to solve differential equations, and to model financial markets, among other things.

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