To simplify $\sqrt{40}$, we first factor the number under the square root:

$40 = 4 \times 10 = 2^2 \times 10$

Now, take the square root:

$\sqrt{40} = \sqrt{4 \times 10} = \sqrt{4} \times \sqrt{10} = 2\sqrt{10}$

So, the simplified form of $\sqrt{40}$ is:

$\boxed{2\sqrt{10}}$

Would you like more details on this, or do you have any questions?

Here are 5 related questions you might want to explore:

1. What is the square root of 90 in its simplest radical form?
2. How do you simplify $\sqrt{72}$?
3. Can you explain how to factor a number under a square root?
4. How do you simplify cube roots, like $\sqrt[3]{54}$?
5. What are perfect squares, and how do they relate to simplifying square roots?

Tip: When simplifying square roots, look for the largest perfect square that is a factor of the number under the radical sign.