Does the water fall or rise

4 stars

A man rowing a boat in a lake throws his anchor into the water

Does the water level rise or fall?

(answer below)

Assuming the anchor sinks, the water level will fall

Whilst the anchor is in the boat, it displaces the volume of water equal to the weight of the anchor

When thrown in the water, it displaces less volume of water (since the mass of the anchor is greater than the equivalent size of mass of water)

Less water displaced means the water level falls



  • Moderate
  • Hard
  • Logic
Submit your vote:



the water would rise
- karen (22 Apr 2009)

My guess is that it would fall. Why? because when the anchor was on the boat, the boat was deeper in the water. But when he took the anchor off, the boat lost weight, so in terms, the water level would fall, making the boat rise.
- Lisa (24 May 2009)

The water level stays the same. Why? The boat with all its load displaces a certain amount of water and the anchor with its weight is part of, throw it in the water it still displaces the same amount.
- Horst (29 Jul 2009)

yes it displaces its weight but The anchor sinks because it is more dense therefore its volume is less than its displaced water
- Jason (16 Nov 2009)

beacuse it falls then whn the sun comes out it picks it up then pass it to the clouds the it drops again
- annie harris (13 Jan 2010)

The water level would fall. When the anchor is in the boat it displaces an amount of water equal to its mass. When the anchor is in the water it displaces an amount of water equal to its volume.

This does assume that the anchor sinks and is therefore more dense than water.

Example: Steel anchor with a volume of 1 litre and a relative density of 7.8.

In the boat the anchor is floating and therefore displaces 7.8kg of water (7.8L).

Out of the boat it only displaces its volume (1L).
- Simon (1 Mar 2010)

THe water would fall and rise because the water would Splash
- Izzy (11 Apr 2010)

neither. it is still moving the same amount of water .
- whatev' (20 Dec 2013)

"displaces the volume of water equal to the weight of the anchor"? Volume (m^3) cannot equal weight (N)
- Part time physicist (11 Jun 2014)

The water would rise because, if you have a cup of water,and you put a mini ball in the water the water would rise. Same thing would happen With an anchor in a lake. The water would not rise that much, but there would be a small difference.
- Emma (18 Sep 2015)

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