# Steel Sphere Density Kit

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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?

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.

**Suggested Activities:**

- 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 sphere.
- 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.

Answers:

- 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 Question**

Apr 7, 2014 | By K. Emde

The demo is great, but we are having issues with density of the small sphere.
Steel should be 7.75 - 8.05 density. We keep getting 6.7 g/cm3. Would the chrome covering make that much difference?

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

The density shperes serve their purpose in the explanation of density. They are supposed to weigh about 150 grams. In weighing them in our lab the students were not happy about the mass of each sphere. The smaller sphere weighs 128.6 grams and the larger 142.5 grams. The students were supprised by the difference in weights and what the product was supposed to weigh.

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

I use this as one of the stations to explore density. Students understand it is not size that provides buoyancy rather material.

**Great to use introducing density concepts!**

May 23, 2012 | By Donna Brown

I love passing these around the classroom and then having students form hypothesizes about which has more mass, will they float etc. They never ceases to amaze! It's well worth the $ to add these to your classroom materials. It's a demo your students won't soon forget!

**Density Balls**

May 23, 2012 | By Nancy

These density balls are a good way to help students understand why a ship can float. The large ball is easily dented.

**Great Density balls for math and science**

May 22, 2012 | By Aaron Geery

These are great for showing and working the density formula for both math and science class.

**Steel Spheres**

May 18, 2012 | By Paula Borstel

I have used these 2 spheres for several labs and demos. 1) The students hold each and predict which one weighs more. 2) The students predict if there will float or sink. 3) We use them to discuss pressure, and show how the force (weight) over area determines the pressure. 4) We predict which one will roll the fastest down a ramp. Usually most students are surprised at the results! Great for correcting misconceptions!

**Steel Density Kit**

May 16, 2012 | By Ken Pinkerton

Excellent demonstration and investigation into density. The diffence in the spheres sizes provides a wonderful investigation and is thought provoking and concept builder. Get it, you won't regret it.

**Density spheres**

May 16, 2012 | By Judith L. Schriver

I use these in my lesson on density. The students are amazed that the large sphere floats but yet is more massive that small sphere. Wonderful tool for teaching density.

**Great fun and learning**

May 16, 2012 | By Daryl Kuhn

If you pretend the larger sphere is hard to pick up, the floating will fool them every time. A great kick off to density lessons. Calculations of the density of each add a level of difficulty/challenge for students.

**Watch Their Jaws Drop!**

May 16, 2012 | By Kate Treatman-Clark

Every time I've done this experiment in a class I ask the kids to feel the two balls and decide which is "heavier". They invariably choose the larger ball and are astonished when it floats while the smaller, denser ball sinks. Then we put the balls on the scales and they are again surprised to see that there is almost no difference in mass. I really can't think of a more elegant or more fun way to introduce density!

**Useful**

May 16, 2012 | By Diedre Adams

I love these to demonstrate not only density, but pressure. The students think the small sphere has more mass because of the limited area on their hands. Great teaching tool.

**Excellent way to explain density**

May 16, 2012 | By Scott

This is probably one of the easiest methods I have found to explain density to younger students.