As every beleaguered middle school biology or high school chemistry teacher pleaded, science is fun. While balancing chemical equations and trying to stomach a dissection might leave you with a bad taste in your mouth, remember that the simple science concepts can be pretty amazing to discover as a kid. So with that in mind, enter the banana hammer.
It's admittedly straightforward, as far as scientific enquiry goes. What happens when you leave a banana out in the freezing cold? To most of us world-weary adults, the answer might not seem so exotic. But to a child who is just learning about the effect of temperature on water, the presentation might just blow their little minds.
It really is as easy as putting the banana in the freezing (very freezing works best) cold. Ask the kids what will happen to the banana. Will it get softer? Harder? Will it grow bigger or smaller, like the balloon trick we just learned? After the banana is thoroughly frozen, ask the little one to inspect it. And then totally blow the kid's mind when you show them that the banana is so rigid that it can actually hammer a nail into wood. Explain that it's the water in the banana that freezes, just like the ice cubes in the freezer.