Gravity is the most mysterious of the forces we experience in our lives. Impossible to screen against, it extends throughout space to the farthest corners (corners?) of the cosmos, causing every piece of matter in the Universe to affect every other. Wow!
More prosaically, gravity gives rise to the phenomenon of ‘weight’ – the force which pulls us ‘down’ to the Earth. GCSE students are tutored on the difference between mass and weight, and are told that the weight of an object, say a Gnome, varies from one planet to another, but its mass is the same on any planet. However, the Kern instrument company are keen to point out that if you use a sensitive force balance, its weight changes from place to place around the Earth.
The balance doesn’t even need to be that sensitive. I was surprised to find out by how much the weight of an object measured at a fixed height above sea level changes with latitude and longitude: – it varies by around 0.5%. So for a Gnome weighing around 300 g, changes of 1.5 g should be seen and this is easily detectable. The rationale for the publicity stunt is explained here, and you can follow the Kern Gnome on his journey here. I like this experiment because the measurement is so simple – and yet the physics it uncovers is so profound.
The light-hearted video below shows my children’s reflections on the mystery of Gravity.
P.S. After a period of steady decline, my own weight has been mysteriously increasing. I think this may be due to a fluctuation in the gravitational constant G. More about this in future articles.