What is a Congruent Shape?
This video provides detailed examples and explanations of congruency of shapes and angles. A congruent object is a shape that can be flipped, turned, or slid to make the same shape. All the sides of each congruent shape must be identical. One way you can move a congruent shape is by turning or rotating it. Another way is to reflect it, that is, flipping the object across its axis. The final movement is translation, moving the shape by sliding it in any direction.
What happens when I take this object, and I flip it? It looks pretty different right? But aren’t all the sides still the same? If I flip it back, we can clearly see that the two objects are the same.
This is what we call congruent objects – shapes that can be flipped, turned, slid to make the same shape. All the sides of each shape must be identical.
There are a few different ways you can move congruent objects. Moving the object using one of these three movements may change the position or the way the shape looks, but the shape itself will always remain the same.
The first movement we will talk about is a rotation. One way you can move a congruent shape is by turning it or rotating it. This movement is called a rotation.
The second movement is a reflection. A reflection happens when an object is flipped across an imaginary line or axis. It’s almost as if the object is looking at itself in the mirror.
The third, and final, movement is a translation. A translation happens when you move a shape by just simply sliding it in any direction. So you are not turning it or flipping it, you are just sliding it.
Okay, now it’s time to take a look.
These two triangles are congruent, but they have been flipped across the y-axis. So, this is a reflection. It is still the exact same triangle, the only difference is that it has been flipped .
These two triangles are congruent as well ,but they have been rotated or turned. This is a rotation. The two triangles are still the same, they have just been turned.
These two arrows are identical in shape and in size; so, we know that they are congruent. However, they have been slid upwards. This movement is a translation. Again, the two arrows are they same; they have just been slide upward.
Okay, now it is your turn to practice.
Identify if the following shapes are congruent or not. If they are congruent, then identify how they have been moved – by reflection, rotation, or translation.
Are these two shapes congruent?
No, They are not congruent. We can see that they are different sizes, and one star has six points while the other only has five. To see this more clearly we can place them on top of one another.
Are These two shapes congruent?
Yes! We can see that they are identical, however they have been moved. What type of movement is this? Well, it looks like they have just been flipped, right? If we imagine that there is a line through the middle, we can see that they have been flipped across the line. This shape has been reflected.
Are these two shapes congruent?
No. We can see that they are different sizes by placing them on top of each other.
Okay, last one. Are these two shapes congruent?
Yes! They are identical in shape and size, but what type of movement has been made? Was it flipped like the last one? No. So it’s not a reflection. Has it been turned or rotated? No, so it’s not a rotation. Has it been slid? Yes, so we know that it is a translation.
Great work guys.
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