# Physics 27 Making Walls Stronger

Changing the shape of a sheet of paper made it much stronger. But people don’t live or walk on tubes or folds. People live in buildings with walls.

The sheet of paper got stronger when forces were moved from the center to the edges of the paper. Can walls do the same thing?

Question: How can walls be made stronger?

Materials:

Paper

Tape

Ruler

Scissors

Procedure:

The physics project will use nine tubes of about the same diameter.

Make 9 small diameter long tubes of paper

The four tubes for the square must be shorter than the two used for the diagonal pieces. The distance diagonally across the square is farther than across a side.

Trim 6 cm off the ends of four tubes

I put each left tube on top of the right tube so the square would be close to a square not a rectangle. You can do the opposite as long as you do the same for each corner.

Tape the four trimmed tubes into a square

A strip of tape across each corner on both sides held the tubes in place. The tape wrapped around the tube at each end about half way.

Hold the square in one hand or with the bottom on a table

The tape crossing each corner holds the square together. Is the tape strong enough to hold the square together?

Push the side

Pushing on one side of the square makes the side slope. All the pushing force goes across the top tube to push on the top far corner making it buckle.

Tape a tube diagonally across the square

The diagonal tube is taped into place. Notice the tape itself stiffens the corners.

Hold the square in one hand or with the edge on a table

Putting a diagonal inside the square wall cut it into two triangles. Pushing on one side with another side of the triangle on the table is like pushing on the triangle. The side does not move.

Push gently on one side then the other side of the square

Tape a tube diagonally across the square in the other direction

Both diagonals must be flattened a little in the center so the two diagonals will lie flat.

Hold the square as before

Push gently on one side then the other side of the square

Laying the tubes out for the triangle shows that each corner has less angle than those of the square.

Tape three tubes into a triangle

The tubes meet at an angle so I flattened the tips a little and taped over the top of the joint.

Hold the base of the triangle in one hand or on the table

Push on one side then the other side of the triangle

Observations:

Describe how the square feels to hold

Describe what happens when you push on the sides

Describe how the square with one diagonal feels

Pushing on the side of the square with one diagonal going up makes the square twist. The pushing force tries to push on the far corner but the diagonal tries to take the force back to the table not letting the corner move.

Describe what happens when you push on the sides

Describe how the square with two diagonal feels

Describe what happens when you push on the sides

Describe what the triangle feels like when you hold it

Describe what happens when you push on the sides of the triangle

Conclusions:

Is a plain square very stable? Why do you think so?

Why did you have to trim the four tubes for the square?

What has the square become when you add a diagonal?

The triangle side does not push over. The force goes down the other side and into the table.

Compare how the square with a diagonal and the triangle act when pushed on.

Compare how the square with two diagonals and the plain square feel when you hold them.

Compare how the force of a push on the plain square compares to the force of a push on the square with one or two diagonals.

Why do you think the diagonals make a wall stronger?

Can you think of another way to make a square wall stronger with out using diagonals?

Try your idea out and see if it works. Compare your method to the diagonal method.

What I Found Out:

The plain square was very flimsy. It was easy to push the side over turning the square into a rhombus. This is not very stable.

The longer tube fit into the square. If the sides had not been trimmed, the longer tube would not have been long enough to reach across the diagonal.

Once the diagonal is in place the square becomes two joined triangles. It feels much stiffer than the plain square did. The sides do not push. The square does twist when I push on the side.

The sides of the triangle did not move when I pushed on them. The triangle felt rigid.

The square became two triangles with the diagonal in place so the sides did not want to move. But pushing on the top triangle made the side twist because it was not flat on the table.

Pushing on the side of the square with two diagonals in it has the forces being split so some goes across the top, some from the top to the bottom down the diagonal even some into the second diagonal. The square will not push.

With two diagonals in it, the square is stiff. It feels rigid, not at all flimsy like the plain square. The sides do not move when pushed. It does not twist.

When I pushed on the side of the plain square, all the force went across the top tube to push on the other side tube. It moved.

When I pushed on the side of the square when the diagonals were in place, some force still went across the top. But some of the force went down the diagonal to the base of the square.

Diagonals make the square stronger by redirecting the force, breaking it up. That way less force pushes on the top of the side tube and it doesn’t move easily.

The square gets stronger if the corners do not move. Diagonals move the forces around. If the corners are reinforced somehow, it would take a lot more force to move them.

One way would be to put small diagonals across each corner. Another way would be to put a solid piece over the entire square to hole the tubes in place.