I’m not a physicist, and I’d always supposed that, while the Earth has a significant gravitational pull because it’s so massive, the gravitational pull between everyday objects must be completely undetectable, or maybe only detectable with modern laboratory equipment.
But I only thought that because I never bothered to actually plug in any numbers. Using the formula for the force of gravity, you can see that if you have two 1-kilogram objects 0.1 meters apart, the acceleration due to gravity between them is enough to move them by 2.7 millimeters in just 15 minutes. Wow!
Of course, this makes sense, given that was measured all the way back in 1798 by Henry Cavendish. I think I knew that was measured quite long ago, but I just assumed it was based on some astronomical calculations, or was some sort of indirect inference. Nope, it turns out Henry Cavendish put some lead balls on a torsion balance and directly measured how much they attracted each other. Cool!