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**Investigation 2 Weight Watching**

Part 1 Setting A Standard

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**What unit is used to describe the mass of an object?**

Essential Question What unit is used to describe the mass of an object?

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Essential Question What unit is used to describe the mass of an object? The gram is used to describe the mass of an object.

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**What is heavier? A book or a pencil?**

Question What is heavier? A book or a pencil? A book is heavier because it has more mass. Mass is the amount of stuff in an object. The book has more stuff than the pencil, so the book is heavier than the pencil.

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Task Your task is to put three objects in order from heaviest to lightest: a washer, a wood square, and a plastic chip. Have getters get the materials. Have reporters report the order of the objects from heaviest to lightest. Discuss any discrepancies among the ordering. Do the objects feel about the same in weight?

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**The Balance The balance has two parts – the balance beam and the base.**

The point of the base on which the balance bean rests and pivots is the fulcrum. Cups go into the holes in the balance beam.

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Assemble the Balance When the balance pointer lines up with the raised area on the base, the system is balanced. When the system is not in balance at the start, you use the slider to zero the balance. When two objects are placed in the cups the heavier one will go down.

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**Using the Balance Getters get two cups.**

Use the balance to verify that you have placed the three objects in the correct order by weight.

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Units Sometimes it is fine to just compare objects to find out which object is heaviest, but at other times, it's important to know how much an object weighs. The balance can be used to weigh objects if some kind of units are available.

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**Weighing in Paper Clip Units**

Put the object to be weighed in one cup on the balance. Put paper clips in the other cup until the beam is even or balanced. Count the number of clips that were needed to balance the object.

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Weighing the Washer Each group will get a paper cup of paper clips and a sticky on which to record their information. Weigh the washer using the paper clips. Reporters report the results. Draw a chart on the board and record the weights. Ciscuss the discrepancy.

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**Discuss the Results Did everyone get the same answer?**

What could some of the reasons be for different answers? Compare these results with the results when they measured with the straws. If you weigh the same object, but use different-size paper clips you are going to come up with two different answers. Ask for suggestions as to how we can solve the problem.

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The Gram What we need for reliable measuring is a standard the everyone uses. The standard unit for measuring mass is the gram. Show the students the 5-g, 10-g, and 20-g mas pieces.

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**Weighing With Standard Mass Units**

Getters, get a mass set. Use the mass set to weigh the washer, wood square and plastic piece and determine their mass. Record the measurements on your sticky.

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**Return the materials to the materials station.**

Collectors Return the materials to the materials station.

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Student Sheet Cut out the steps on the Steps for Weighing an Object sheet and put them in order on the other sheet of paper. Glue them in order with your glue stick.

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**Vocabulary Record these vocabulary words in your science journal.**

Balance – a tool used for weighing objects, when the balance beam is level, the objects on either side are equal in weight Fulcrum – the pivot point on which the balance beam rests

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Vocabulary Gram (g) – the standard unit of mass in the metric system; 1 gram is the mass of 1 cubic centimeter (or 1 mililiter) of water at 4 degrees C. Mass – a measure of how much stuff is in an object

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**Content/Inquiry Why is it important to have a standard unit?**

What is the standard metric unit for mass? A standard is necessary for consistency among measurements The gram (g) is the standard metric unit for mass..

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