Science Buddies has many projects where you build something with moving parts or do an experiment with the physics of moving objects. Here are just a few examples, but this is not an exhaustive list! You can search our site to find many more.
Ball launcher (Figure 1)
Marble roller coaster (Figure 2)
Rube Goldberg machine (Figure 3)
Build A Wall Marble Run (Figure 4)
Figure 1. A catapult-style ball launcher.