Hi All, I have a problem (with 3 separate instances) to which I believe I have the answers, but would like check with those more knowledgeable than myself. They revolve around 3 blocks sinking through water and which falls quicker. I am ignoring friction. Instance 1: All blocks are exactly the same shape and size. They have different masses however. Which falls quicker? Instance 2: All blocks are of different sizes (short/medium/long), but have the same mass. Which falls quicker? Instance 3: All blocks are made of the same material but are different sizes (short/medium/long). Which falls quicker? My understanding of the answers is based upon Newton's second law, buoyancy and free body force diagrams: W(obj) - W(wat) = mass of object x acceleration (where Weight of water is equal to its density x volume of object x gravity): a- ( m(o) - m(w) ) g = m(o) a b- ( p(o) - p(w) ) vg = p(o) v a (mass = density x volume) 1. Using eqn a: Although m(o) increases, m(w) remains constant, therefore acceleration increases and heavier mass falls quicker 2. Using eqn a: As they have the same mass, m(o) remains constant, but m(w) increases as the size of the object increases. Therefore, the smaller object falls quicker 3. Using eqn b: All densities are equal, but as the volume on both sides of the equation cancel each other out, they fall at the same rate Is this the correct understanding? I believe it is, but it does do your head in!!!