1. The problem statement, all variables and given/known data A beaker is filled with water and its weight is measured by a balance scale. The reading is recorded as R1. 1. A ping pong ball is now submerged in the water without touching the wall and the bottom of the beaker. What is the reading, R2 of the balance scale? 2. A steel ball with the same volume as the ping pong ball tied to a light thread is now submerged in the water without touching the wall and the bottom of the beaker. What is the reading,R3 of the balance scale? 3. The same steel ball is put into the beaker without the thread, it sink to the bottom of the beaker. What is the reading,R4 of the balance scale? 4. Back to question 2, but now instead of a stationary steel ball submerged in the water, we make the steel ball moves upward with an acceleration a. Should the reading R5 be R5=R3, R5>R3 or R5<R3? 2. Relevant equations Newton Second Law F=ma, Newton Third Law F1 = -F2 , Weight = mg , Pressure exerted by the liquid= Force/ Area = density x gravity x height of liquid 3. The attempt at a solution 1. When a ping pong ball is submerged in the water, some water is displaced by the ball. The weight of the ping pong ball is balanced by the buoyant force of the water. Since the water is now displaced to a higher level, the bottom of the beaker experienced more pressure than a beaker filled with water only, thus R2 > R1. I am uncertain if my concept is right. If so, how do i explain this in terms of Newton's Law? 2. I think the reading for this one, R3, should be the same as R2 with the same explanation. 3. When the steel ball is sunk to the bottom of the beaker, it exerts its own weight to the bottom of the beaker. Therefore, the balance scale has 3 forces acting on it, the weight of the beaker, the weight of the water and the weight of the steel ball. R4 > R3 > R1 4. I believe this can be solved by using Newton's Law of Motions. My intuition believes the reading R5 should be bigger than R3 because by newton 2nd law, the normal reaction of the scale, N = Resultant force,F + Weight of beaker and water, W. But I dont really understand why does the scale displays the magnitude of normal reaction(which is an upward force), instead of the weight(which is downward force). I do not know the answer for these questions, so my answer might be wrong.