How to write two dot above a letter?

Question

the two dots above a letter represents two derivative of varible t.

My method:

\documentclass[UTF8]{ctexart}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{epstopdf}
\usepackage{inputenc}
\begin{equation}
\"{o}
\mathaccent{o} 
\end{equation}

However,the latex says in the math environment ,I must use the \mathaccent. So I replace \" by \mathaccent, but it shows the warning information: Missing number, treated as zero

I am a starter, I want to know how to revise it? Can someone help me? Thanks sincerely!!

Answer 1

The sequence

\"{o}

will be used when you want to write 'ö' in text, such as 'Schrödinger'. While in the math mode, as Peter Grill mentioned

\dot{o}
\ddot{o}

and so on, should do the trick.

Edit:

For more than two dots, e.g. \dddot{o}, you need the package amsmath, which allows you a maximum of 4 dots \ddddot{o} (not strikingly beautiful )

For higher dot derivatives take a look at this post