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« Golf Ball vs. Lead Fishing Weight | Main | Sinking and Floating Bubbles »

Does Mass Affect the Sinking/Floating of Objects?

Students have a major misconception that mass determines whether an object floats or sinks. This is an activity that forces students to deal with that misconception and hopefully break it. The following materials are needed:

  1. large pumice stone
  2. Density Sphere Experiment Kit
  3. large fish tank of water 

Have the students read the statement, "Objects that are high in mass, sink in water." Have the students show in some way if they agree with the statement, disagree with the statement, or are somewhat in between. Have them explain why they think that way and give examples. Then present the students with the list of all of the items to be placed into the tank, arranged according to their masses. Do not show the objects to the students. Have them write a hypothesis for each item (on whether they will sink or float) based only the property of mass. Then drop each item one by one, in order of their masses, into the water. Have students record the results. The students will realize that mass has nothing to do with whether an object sinks or floats. Then show the students the objects' densities. Hopefully they see the pattern of those objects with densities less than one float, and those with densities greater than one sink. It is not important to explain what density is at that point, but just that it is a property of matter that is vital in determining if an object floats or sinks.

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Reader Comments (4)

Since floatation is shown here to be a function of density, I would recommend allowing the kids in pre-classes determine and know what mass, volume, and eventually density are. Not explaining 'density' at the time of the floatation lab won't actually convince them, since they don't know what it is.

June 3, 2012 | Unregistered CommenterIbrahim Kai-Samba

"This was such an informative post. I have definitely learnt a point or two from this.
Great work!. Keep ém coming."

This video is great. I teach fourth grade science and my students have been really struggling with the concept of density. The misconception that the more massive an object is, the more likely it will sink rings true with my students. I love how you tried so many different object as well.
I wonder if it's possible to set this up as a lab for them. Have them create hypothesis on whether things will float or sink, then let them test it out. The gears in my head are turning now, thanks for the video.

October 10, 2012 | Unregistered CommenterV. Bash

thanks, this video is really helpful

October 11, 2012 | Unregistered CommenterGMH

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