Added: Double Atwood’s Machine Experiment;

Improved: simplify operations; Improved: add physics and math descriptions; Fixed: crash-error caused by rotating screen;

Improved: set default language to English;

fixed: device model compatibility issues;

improved: norm the notations about vector;

improved: Add sound effects;

improved: Adapted to new iPads; improved: Some performance optimizations; fixed: Abnormal showing of Parabolic movement exp and Uniform circular motion exp in iOS9 devices; fixed: Abnormal window layout when rotating the screen;

improved: Uniform circular motion exp adds relationship with the simple harmonic motion; improved: Simple pendulum exp can show centripetal acceleration now; fixed: some inputboxes be covered by keyboard in some exps; fixed: low precision question in energy bars;

improved: change operation ways of Friction exp, make it more reasonable; improved: add choice-show periodic function [support dumping] in Work&Energy exp2; improved: add new exp: mechanical vibration - Single pendulum exp; fixed: rounding errors in some figures;

fixed: 2D function's horizontal line overlay on y-Axis name in main scene; improved：Add progress bar to indicate rpm in main scene of uniform circular motion experiment; improved: some performance optimization;

improved: Parabolic movement experiment adds location circle; improved: Work&Energy experiment 2 adds hint when the block is selected; fixed: Strings overlapped in free-body-scene in Work&Energy experiment 2;