Teacher:
Grade/ Subject: Grade 3 Science
Unit: Building with a variety of
materials
Topic: arch Bridges
Date:
Length of Lesson:
Outcomes
3-1 investigate the nature of things, demonstrating purposeful action that leads to observations and
inferences.
3–2 Identify patterns and order in objects and events studied; and, with guidance, record observations, using pictures,
words and charts; and make predictions and generalizations, based on observations.
Learning
Objectives:
Students will learn bridge vocabulary
Students will demonstrate the importance of a keystone in an arch figure
Students will observe the increased strength that an arch adds to a structure
Materials
Bridges notebook file
Pool noodle (or bendable ruler, just to show a bending arch)
Plastercine, divided up into balls slightly smaller than a ping-pong ball (7 balls or an add number)
2 stacks of textbooks
2 long strips of manillatag – long enough to have a good span between textbooks and for one to arch (I
premeasured how long I would need to make that piece)
A container to hold pennies
Numerous pennies or other small weights
Review – we made beam bridges last class. what types of tricks did we find out about strong beams?
- Accordion fold worked well, having a few layers helped, the folds had to be the long way not the short way, etc.
- Show the previous notebook slides about certain folds that worked the best.
Today We are going to learn about a new type of bridge – show the slide with arch bridges, let them try to predict what kind
of bridges we are looking at today – remove the square in the middle to reveal if they are right!
Point out the Ukrainian Friendship Arch – it isn’t a bridge but we will be learning about it in Social this week so I put it on
here!
Why would we use an arch bridge?
- the arch bridges are used to span a deep gap (eg. valley). They are one of the cheaper bridges to build.
How they used to build them: (the image with stones and wood)
- build up the supportive edges (called abutments).
- use a wooden support to lay the bricks around.
- the keystone is the final piece - it holds everything together. It is the piece in the very top that is in the
middle.
When weight goes on top of an arch, it pushed the weight down to the bottom.
Show a pool noodle, bend it in the air– it bends easily, but it doesn’t stay that way on its own and if I was
to try and put a book on top of it, the arch would flatten out. This is why we need abutments – put two
chairs (or hold noodle in place with your feet) as abutments to show how it can now stand on its own. So
the abutments are important and they have to be strong!
The other term we just learned about was a keystone, I want to demonstrate how that piece works.
Stack 3 plastercine balls in a slight curve, squish them down into the desk a bit so that they stick. Then do
the same with another 3, then emphasize how they stick together when you put in the keystone - see how
it stands on its own? - put a textbook on top. Keep adding textbooks until it squashes. NOTE: you could
do 2 equal arches and put a textbook on top if it doesn’t stand on its own good enough or you can do 2
arches and secure them with a textbook on either side as abutments to form more of a “bridge” look)
Next we are going to try being arch bridges using our
bodies – pair students off.
Show them the picture and demonstrate. Stand a few
feet apart. Put your hands together above your head,
lean forward into their hands. Your hands are like the
keystone here, without the other person’s body you
would fall over!
Use one group as an example – have them get ready to
lean their hands together, but then place a textbook
between their hands before their hands join together.
THIS is like the keystone piece being put into place.
Their bodies are keeping the textbook in place.
Is it easy being an arch bridge? No! these arches work hard! We have one more experiment to try.
Get someone to Hand out handouts while you set up the textbooks for the next experiment – fill in the first
blank with the word “keystone”
First set up the books, put the piece of manila tag laying across it.
Predict how many pennies the piece of paper will hold. Add one penny
at a time until the piece of paper falls through.
Now use the 2nd piece of manila tag to wedge it between the lower
textbooks, pull it up in the middle until it reaches the first piece of
paper. Point out that this piece of paper is secured by being wedged in
to the abutments (the texbooks). Predict how many it will hold now that
it has an arch.
Compare results. Fill out the worksheet with your findings from today,
go over the answers as a class to summarize.
NAME: _____________________________
Observing Arch Bridges
What is the middle “rock” on an arch called?
________________________.
What does a straight beam do when we put
weight on it?
___________________________________________
What happens when we put an arch under it? ____________________
__________________________________________________________
Draw a diagram of our experiment: (label the abutments, the beam, the
weight, and the arch)