Angle Inspector
An angle tester is made from two strips joined so they can turn around the same point. That joined point is the pivot. Put it at the corner you want to test and align each strip with one side of the corner. You have now copied its opening.
Before you try
How could you carry a corner’s opening from one object to another?
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Interactive activity
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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 20–21).
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Try these ideas
- Copy a narrow opening before trying a wide one.
- Compare a tester with a right-angle reference.
- Draw the copied angle with longer arms and check that it still matches.
Why it works
An angle tester is made from two strips joined so they can turn around the same point. That joined point is the pivot. Put it at the corner you want to test and align each strip with one side of the corner. You have now copied its opening.
Carefully move the tester to a second corner without changing the distance its arms have opened. Line up the pivot and one arm again. If the second arm also lies along the other edge, the two angles match.
A book or pencil-box corner can provide an L-shaped reference. An opening smaller than this is acute. A larger opening, before the arms form a straight line, is obtuse. In Copy a Corner, draw the missing arm so its opening matches the small reference. The game straightens an accurate stroke into the copied angle.
Worked example: Your tester fits a book corner and then a table corner without changing its opening. What do you know? Both arms line up at the first corner. The unchanged tester also lines up at the second. The two corner angles are equal; if they are square corners, both are 90°.
Check your understanding
Question 1 of 2
Where should the tester’s pivot go?
One arm lines up, but the second does not. The angles…
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
For parents & teachers
- Card-strip tester · 10 minutes. An adult joins two card strips with a paper fastener. Compare the corners of a book, box and ruler.
- Copy without numbers · 5 minutes. Show a tester opening, hide it and ask the child to sketch a similar opening. Bring the tester back to compare.