How are they the same?
How are they different?
One floats and one doesn't! Which is which?
Great for teaching the skills of observation and deduction! Although these two shiny, metal spheres have about the same mass, one has a diameter significantly smaller than the other, making their densities vastly different. Seeing the large one float in water seems unbelievable! Bowl not included.
Read more on our Blog - Demonstrating Density: Who Knew They Could Be So Dense?
Download the pdf of our newest lesson!
Download the pdf of the lesson below!
Two Steel Spheres
How are they alike?
How are they different?
Which sphere floats in water?
Great for teaching the skills of observation and deduction! Although these two shiny stainless
steel spheres have nearly identical mass, one has a diameter of 3.49 cm, and the other a diameter
of 12.7 cm. Seeing the large hollow one float in water seems unbelievable! Great for teaching
that density depends on BOTH mass and volume.
- Ask students to observe the two spheres set on a table and predict which one is heavier
and by how much. Ask one student to hold a sphere in each hand and estimate which one
is heavier and by how much. The common erroneous answer is that the smaller one is
much heavier. Follow this up by asking a blindfolded student to hold two small identical
plastic containers, one in each hand. Place a sphere in each container and ask how the
masses compare. The common answer now is that they both weigh the same. Discuss
how we perceive the mass of an object.
- Place the large sphere in a container of water. Students are amazed to see it float. What
does this tell you about its density?
- Math Problems:
- If both spheres weigh about 150 grams, calculate the density of stainless steel.
What assumption did you make?
- Using the calculated density of stainless steel, calculate the thickness of the large
- Knowing that the large sphere has a mass of about 150 g, calculate how much
additional mass could be placed inside the sphere and still float.
- In the last problem, if twice the calculated mass is added to the inside of the
sphere, would the resulting object float or sink?
- Calculate the mass of the large sphere if it were solid.
- 6.7 g/cm3 – Base the density on the small sphere, assuming that it is solid.
- 1.1 mm
- Less than 920 g
- If placed inside, it sinks. If placed outside, it depends on the density of the
additional mass, whether it is more or less dense than water.
- 7,190 g or 7.19 kg
Write a review
Density spheres demo
Aug 31, 2016 | By Kevin Collins of Boise, ID United States
Apr 7, 2014 | By K. Emde of Edmond, OK United States
Owner Response:Good question! According to the technical specifications of the material, the smaller sphere is made of stainless steel and is not chrome plated. That said, the density is supposed to be 8 g/cm3, which is clearly not what you're getting. I will reach out to our supplier to see if they can shed some light on the subject.
Good but not good enough
Feb 11, 2013 | By Andy Howe of Maryville, TN United States
Owner Response:Hello Andy, I'm sorry your spheres were so far apart in mass. Our in-house specifications are for the two spheres to be within 10 grams with the larger one being more massive. We are happy to replace these for you.
excellent for stations
Jun 5, 2012 | By susan wanzer of phoenix, AZ United States
Great to use introducing density concepts!
May 23, 2012 | By Donna Brown of Hoschton, GA United States
May 23, 2012 | By Nancy of Cleveland , AL United States
Great Density balls for math and science
May 22, 2012 | By Aaron Geery of SLC, UT United States
May 18, 2012 | By Paula Borstel of Rancho Palos Verdes, CA United States
Steel Density Kit
May 16, 2012 | By Ken Pinkerton of Fortuna, CA United States
May 16, 2012 | By Judith L. Schriver of Warfordsburg, PA United States
Great fun and learning
May 16, 2012 | By Daryl Kuhn of Burlington, VT United States
Watch Their Jaws Drop!
May 16, 2012 | By Kate Treatman-Clark of Edgewater, MD United States
May 16, 2012 | By Diedre Adams of West Terre Haute, IN United States
Excellent way to explain density
May 16, 2012 | By Scott of Elmvale, ON Canada
This product will support your students' understanding of the Next Generation Science Standards (NGSS)*, as shown in the table below.
Suggested Science Idea(s) 2-PS1-1
| Elementary || || Middle School || || High School |
| 2-PS1-1 |
Students can use the Steel Spheres Density Kit in an investigation to describe and classify different kinds of materials by their observable properties. 2-PS1-2
Students can analyze data obtained from testing the two spheres in the Steel Spheres Density Kit to determine which materials have the properties that are best suited for an intended purpose. 3-PS2-1
Students can use Steel Spheres Density Kit in an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object. 5-PS1-1
Students can use the Steel Spheres Density Kit in an investigation to develop a model to describe that matter is made of particles too small to be seen. 5-PS1-3
Students can make observations and measurements of the steel spheres to identify materials based on their properties.
| || MS-PS1-1 |
Students can use the Steel Spheres Density Kit in an investigation to develop models to describe the atomic composition of simple molecules and extended structures. MS-PS2-2
Students can use the Steel Spheres Density Kit in an investigation to provide evidence that the change in an object's motion depends on the sum of the forces on the object and the mass of the object.
| || HS-PS1-1 |
Students can use the Steel Spheres Density Kit in an investigation to predict properties of elements. Students can use the Periodic Table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms. HS-PS2-6
Students can use the Steel Spheres Density Kit in an investigation to communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
Students can use the Steel Spheres Density Kit in an investigation to make sense of density and the forces that act upon them, specifically, buoyancy. Secondary students can do the math to determine the density of each sphere. Density is a fundamental property of matter. Density is defined as mass divided by unit volume, Buoyancy is the upward force experienced by a submerged object. The size of the buoyant force on an object submerged in any liquid is the same as the weight of the displaced liquid. The principle of buoyancy is called Archimedes' Principle. 53-PS2-1
Students can use Steel Spheres Density Kit in an investigation about density and buoyancy. Although both spheres have the same mass, effects of balanced and unbalanced forces on the motion of the spheres is quite different. An outstanding inquiry activity.
* NGSS is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of, and do not endorse, this product.