I have a number of science demos that I like to do with elementary students. Some require a little practice or prep time but you soon become confident with them.
I have never had a problem with this demo and have done it dozens of times but I still expect the glasses to go crashing to the floor.
We begin with a discussion of Sir Isaac Newton. There always seems to be one or two students who claim to have heard of him . I have been scared to ask how or where. I talk a little about gravity and the Law of Inertia.
An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
I mention pulling someone on a sled and how you have to use more energy to get the sleigh moving although sleds and toboggans are probably as rare today as hearing about 17th century physicists .
Then we count to 3 and I smash the stick.
Here are a few tips:
1. Originally, I saw this done with pins at the ends of the stick. I don't use them anymore and don't have to worry about losing them. ( I always thought the pins were cheating a bit.)
2. Do not let your significant other catch you using or even looking at the best crystal.
You can pick up some nice wine glasses at most dollar stores. Make sure you use wine glasses because regular drinking glasses don't have the same effect.