Answer to Question #199240 in Physics for Alan Enrico V Tuib

Question

Consider this thought experiment: Put a pan of water on a weighing scale and read the weight. Dip a piece of iron in the water taking care that the lower end does not touch the bottom. Will the reading increase or not? Why and by what principle?

Answer 1

When we dip our finger in the water, the water exerts upward thrust on the finger (Archimedes’s principle). Due to Newton’s third law of motion, the finger will exert an equal and opposite force on the water in downward direction resulting in increase of the weight of water. Thus the reading of the spring balance will increase.