For my A2 physics coursework I am doing an experiment where I am dropping a buoyant
ball into a water tank from different heights and measuring the depth. Unfortunately I am
a bit short on results but so far I have plotted a graph measuring distance vs height and it
is a straight line. I am wondering if this is correct. I assume it is because I know
mgh = fd where f is the buoyant force which will always be constant (assuming the ball fully submerges in the water) and mg is also constant. Also is their anything I am missing out like surface area of the ball - also is it an appropriate subject for coursework - is it complicated enough etc?
- sorry for the rant

Your question is not clear.

What depth and distance are you trying to measure?

Are you dropping the ball from above the water surface?

According to Archimides Law, Net weight inside water = mg - weight of the water displaced by ball

= mg - k (where k will be constant)

So : outside the water, weight = downward force = mg

Inside water, downward force on ball = mg - k

Acceleration inside water = (mg -k)/m

Acceleration outside water = g