Jelly Joint
Four rods joined at their ends can make a square when all four openings are right angles. Push one corner sideways and the frame can lean. Each rod is still the same length, but the openings between neighbouring rods have changed. It is now a different outline.
Before you try
Will a square made from four hinged rods always stay square?
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What happened?
Move a control to see what changes and why.
The game practises one idea at a time with simple drawn pictures. Check the same idea with real objects and your NCERT textbook (Chapter 2: Shapes and Angles, pages 17).
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Try these ideas
- Match an opening smaller than 90°.
- Move through a square position to an opening larger than 90°.
- Notice which corners become narrower while others become wider.
Why it works
Four rods joined at their ends can make a square when all four openings are right angles. Push one corner sideways and the frame can lean. Each rod is still the same length, but the openings between neighbouring rods have changed. It is now a different outline.
In Jelly Joint the rods do not stretch. Only the joints turn. This helps separate a change in length from a change in angle. Compare the solid frame with the target by looking at its corners and the position of the upper rods. A change at one joint affects the rest of the closed frame.
Three fixed rods joined into a triangle cannot keep leaning in the same way. To change its shape, a rod would need to bend, stretch or disconnect. This contrast explains why diagonal braces are useful in larger frames.
Worked example: A four-rod square leans sideways. What stays the same and what changes? The number of rods stays four. Each rod keeps its original length. The corner angles change, so the outline changes.
Check your understanding
Question 1 of 2
A hinged square leans into a rhombus. What changed?
Which frame resists this leaning without an extra brace?
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
For parents & teachers
- Hinged frame · 10 minutes. Join four equal card strips with paper fasteners. Make a square, then lean it. An adult can prepare holes for the fasteners.
- Describe a mystery frame · 5 minutes. One learner describes a frame using its sides and corner openings. Another sketches the description. Discuss which details were useful.