When a bow is used, it is important that an arrow is on the string when the
string is released. If the
string is pulled back and
released without an arrow, the bow will likely get damaged and the archer will likely get hurt.
However, if an arrow is used with the bow,
releasing the pulled back string makes the
arrow fly. Use what you have learned about
energy to explain why it is so important to
have an arrow on the string.