Purpose of the discussion

This discussion will reveal what students are thinking about the question How good are our senses at comparing weight? and their ideas about what information a pan balance does and doesn’t provide.

Remind students that today's investigation question is:

Engage students in the focus question

How did the pan balance help you answer the question “How good are our senses at comparing weight?”

• The pan balance lets you compare the weight of two cubes.
• We had to make a few changes in the order we found using felt weight but not too many.
• The pan balance lets us check the order of the cubes by felt weight especially when the weights were close and it was hard to tell.
• The pan balance doesn't tell you how much more or less one cube weighs than another.

Supporting questions

What was the evidence that one cube was heavier than another?

• The heavier cube made the pan go down.

What do you think we would need if we want to know how much more one cube weighs than another?

• Counter weights such a plastic counting bears, paper clips, washers (that will be used in the next investigations), objects that weigh ounces or grams, etc.

Recap the discussion

Summarize the ideas you have heard. Point out that:

• The class now has more evidence to answer the question "How good are our senses at measuring weight?".
• The pan balance is a useful tool to check the relative weights of any two cubes.
• We would really like to be able to find out how much each cube weighs (this will happen in the next investigation).