Answer, and give a reason. A steel needle sinks, but a steel ship floats…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Answer, and give a reason.
- A steel needle sinks, but a steel ship floats. Why?
- A ship sails from a river into the sea. Does it float higher or lower?
- An ice cube floats in a glass of water, filled to the brim. When it melts, does the water overflow?
Need a reminder? The key ideaShow
Archimedes' principle: the buoyant force equals the weight of fluid pushed aside, . A body floats if it is less dense than the fluid, with the fraction of its volume under. Relative density .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The ship's hull encloses a lot of air, so its average density is less than water's; the needle is solid steel.
Step 2. (b) Higher: denser sea water holds up the same weight with less volume pushed aside.
Step 3. (c) No. Floating, the ice pushes aside exactly its own weight of water. When it melts it becomes that same weight of water, which just fills the space it pushed aside.
Answer: (a) Average density. (b) Higher. (c) It does not overflow.
Watch out. A ship's floating depth depends on the liquid, not on how deep the water is below it.
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