發送短信 : Exploring students conceptual understanding of forces

 __   _    _    _    _____     _    _     _____   
| || | || | || | || |  __ \\  | || | ||  |__  //  
| '--' || | || | || | |  \ || | || | ||    / //   
| .--. || | \\_/ || | |__/ || | \\_/ ||   / //__  
|_|| |_||  \____//  |_____//   \____//   /_____|| 
`-`  `-`    `---`    -----`     `---`    `-----`