We can draw those lines with pressure sensitive effect via instantly adjusting the size of line. But if you want an easier way to achieve it, the pressure sensitive stylus jaja should be a nice solution.
Jaja is an innovative pressure sensitive stylus designed for iPads, Android tablets and other tablets. The digital pen uses high frequency sound to communicate with any device with a microphone. Of course, you can’t hear the above-human-hearing high frequencies, and the 1024 levels of pressure sensitivity allow you to sketch, write, paint directly onto the touchscreen just like normal paper. In addition to offering precise pressure control, the two integrated buttons can be customized for other functions such as erase, color change and more. Apart from that, the pressure sensitive stylus supports Airplane mode, and the built-in USB port lets you charge the stylus with ease.
At preset, the designer of jaja is raising fund on Kickstarter. Pledge $40 will let you own a jaja pressure sensitive stylus. If you’re interested, jump to Kickstarter official site for more details.