[LibGDX]Trying to make Pong, weird ball behaviour, slides on wall?

Here’s the project on GitHub: http://github.com/ericblobb/PongHelp

Whenever I run the game and the ball hits a wall, instead of bouncing off like it’s supposed to do, it sticks to the wall and slides on it. And that’s only for the top wall. For the bottom wall, the ball slides for less than second then drops off the window. I have no idea at what is happening so could any of you guys help?

Thanks.