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The hardwood wheels spin so smoothly that my daughter could lift her heavy backpack all by herself. It’s a simple setup that really teaches how the cord and wheels share the load.

My five-year-old spent a good hour figuring out how to lift a small toy with the pulley system, and the smooth hardwood held up perfectly. I just wish the included cord was a bit longer for more ambitious projects—still, it’s a solid introduction to basic physics.