Transcript Perimeter and Area Day two - Mendenhall-Jr-PLC

PowerPoint created by
Parsheena Berch
Resource: JBHM material
Pictures: Google Images
Perimeter and Area
• Cut-out shape of hand.
• Stamp pad.
• Stamp the entire cut-out hand with your
thumbprints, making sure that all of the white
space is covered.
• Count the number of thumbprints it took to
cover the teacher’s hand and record the
results on the board.
• What did you notice?
• There is a difference among the number of
thumbprints counted.
Why do you think the number of thumbprints
is so different?
• Each person’s thumbprint is a different size
resulting in a different number for many
students.
• You have just covered the area of my hand.
• Do you think that using our thumbprints was a
very accurate measure for finding the area?
Why or why not?
• If you wanted to wallpaper your room, would
you want to count the number of thumbprints
it took to cover the wall? Would that be an
accurate measure?
• Of course not, because your thumbprints
would probably be a different size than your
parents’.
• How would you be able to make a good
estimate of how much wallpaper you needed?
• In order to do this, you would need a standard
unit of measure.
• Sheet of grid paper, glue, and scissors.
• Glue one handprint from the previous activity onto the
back of the grid paper and cut it out.
• Turn the handprint over and count the number of squares
covering the hand.
• Each student should count to verify the area. Have students
report their findings and post them on the board.
• What do you notice about these numbers?
• You should notice that these numbers are a lot closer to
each other.
• Why do you think most of us arrived at approximately the
same number this time?
• We each used the same unit of measure, square units. In
order to find accurate measures, we need to use standard
units of measure. Area is always expressed in square units.
For example, if the grid paper you used was centimeter grid
paper, then the area of my hand would be expressed in
square centimeters.
• You will be exploring the various formulas for
finding the area of a shape.
• Area is the amount of space inside a figure.
• Area – the number of square units it takes to
fill a space
• Geoboards, grid paper, and Handout #1.
• Form a 2 by 3 rectangle.
• This is how to count the number of square units inside
the rectangle to determine the area. You should count
that the area is 6 square units.
• Record the length, width, and area in the appropriate
section on Handout #1.
• Next, form a 3 by 3 square. This is how to count the
number of square units inside the square to determine
the area. You should find that the area is 9 square units
and record the length, width, and area in the
appropriate section on Handout #1.
• You should form 4 additional rectangles on the
geoboards, sketch them on the grid paper, and record
the corresponding information.
• You should discover that the length times the
width of any rectangle equals its area.
• Therefore the formula is, A = lw.
Find the area of the following rectangles without
sketching them on grid paper.
• Length = 5 cm, width = 3 cm
• Length = 1.5 in, width = 2 in
• Length = 3.25 mm, width = 2 mm
• 15 square centimeters
• 3 square inches
• 6.5 square mm
• Share your results and explain your steps to
the class.
• What is the definition of a square?
• It is a parallelogram with 4 equal sides and 4
equal angles.
• That means it is also a type of rectangle.
• Therefore, the length of the square times its
width also equals its area. In this special case
though, we know that the length and width of
the side of the square are the same, which
means, A = s • s or A = s2, where s represents
the length of a side.
• The exponent 2 or “squared”.
• When you see a small 2 to the upper right of a
number or variable, it means that the number
is multiplied by itself. Teach them to read this
as the number or symbol squared.
• Also, teach them that area will be expressed in
square measurements such as square feet,
square inches, square centimeters, etc.
Find the area of the following squares
without sketching them on grid paper.
•
•
•
•
Examples
Side = 4 cm
Side = 1.5 mm
Side = 0.05 in
• 16 square centimeters
• 2.25 square millimeters
• 0.0025 square inches
Independent Practice: (DOK 2)
• 1) Side = 8 yards
• 2) Side = 2.3 feet
• 3) Side = 10 meters
• 64 square yards
• 5.29 square feet
• 100 square meters
Closure:
• We have found perimeter of polygons by using
formulas and/or just adding the lengths of the
sides.
• We have found the area of squares and
rectangles. We have seen when it is important to
be able to do this.
• Do any of you have any questions about this
topic?
Homework:
• Handout #3 from JBHM binder