How can you knock down a wall made of concrete?

Today we continued our science unit about forces. Our key idea is that by playing with and thinking about forces, people can accomplish surprisingly big things. For example, this week we solved the mystery, “How can you knock down a wall made of concrete?”  We watched a video showing the Berlin Wall and discussed how if explosives were used to tear it down it could have damaged other buildings.  We then watched some videos of wrecking balls and then students did an activity where they investigated what happened to a “wall” made of cups when they changed the strength and direction of a paper wrecking ball.  Students worked in small groups to make a wrecking ball and were challenged to knock down the "wall" of cups without knocking down the "houses."  It was amazing to hear the language students were using and having them problem solve how to knock down the cups.