Description
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?
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Lesson Ideas
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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
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NGSS
This product will support your students' understanding of the Next Generation Science Standards (NGSS)*, as shown in the table below.Elementary  Middle School  High School  
2PS11 Students can use the Steel Spheres Density Kit in an investigation to describe and classify different kinds of materials by their observable properties. 2PS12Students 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. 3PS21Students 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. 5PS11Students 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. 5PS13Students can make observations and measurements of the steel spheres to identify materials based on their properties.  MSPS11 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. MSPS22Students 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.  HSPS11 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. HSPS26Students can use the Steel Spheres Density Kit in an investigation to communicate scientific and technical information about why the molecularlevel structure is important in the functioning of designed materials. 
2PS12
5PS11
5PS13
MSPS11
HSPS11
HSPS26
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.
53PS21MSPS22
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.
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