Jan. 30: Buoyancy Activity

How does the reading on a force probe change as you submerge a weight under water? And what does that have to do with buoyancy?

What follows are pictures of an activity we’ll do in class on Thursday. With a student out of school for a week, I needed a way for her to participate in the activity at a distance. This sequence follows the activity nearly frame-for-frame.


Hang a 100g mass from a force probe. Confirm it reads 1N.


Yep, 100g and (approx.) 1N.


The weight is suspended above the water and the force probe reads 1N.


Half-submerged and the force probe reads a little under 1N. Clearly the water’s providing some type of upward force, taking some of the weight off the string.


Fully submerged and we’re reading about 0.9N — that’s about a 10% drop in weight on the force probe.