In my first lesson to a class I have not taught before, I liked to hang a large metal ball in the middle of the teacher's area at about head high. As I walked into the class after the students have settled in, I deliberately walked pass the hanging ball, pull it close to my face to the other end of the room. I would release the ball and start to greet the students.
I can assure you that the students will not be looking at you. Instead they will be watching the ball as it swang to the other side of the room and came back to your face looking like to hit you soon.
As long as you keep steady, the ball will never hit you. But the dramatic effect will sure to hold your students attention to you for the rest of the year.
Here are 4 other dramatic demonstrations from David G. Willey.
Let's make Physics interesting, to the students!