NO FORCE PAIRS - NO MOTION!

Imagine a school bus on an icy road that is so slippery that there is no friction between the tires and the ice. Without friction, the tires are unable to push on the ice. No action force means no reaction force which means, no forward motion. The school bus is stuck, unable to move because it cannot push on the icy (frictionless) – and of course the icy road cannot push back!

Imagine an astronaut who becomes detached from their space station while repairing a mechanical problem. They find themselves stranded in the vacuum of outer space - a region without any matter – not even air! The stranded astronaut cannot walk, crawl, or swim back to their space station because there is no matter to exert a force on. No action force means no reaction force which means no forward motion. Fortunately our hypothetical astronaut was a good physics student and his understanding of Newton’s 3rd Law of Motion is about to save his life – thanks to the wrench he is still holding. Would you know what to do?

The story of the stranded astronaut summarizes the problem confronted by humans who yearned to explore the depths of outer space. How to move forward when there is no matter to push against in the empty vacuum of deep space? Well, that astronaut’s space station did not get there by magic; the solution relies on vehicles that push themselves!

Self-propelled, action-reaction vehicles not only made space travel possible but are commonly used here on Earth as well. How many action-reaction vehicles can you name? See the next post for more on these “self-propelled” vehicles.