Imagine a big truck, called a dumper truck. This truck is super strong and is designed to carry heavy things like sand or rocks. Now, when the dumper truck goes to a place, it stops. Then, it can lift its back part up high. When it does that, all the big, heavy things inside just fall out! It's like when you have a toy box and you turn it upside down to let all your toys come out! The dumper truck does this to help move sand or rocks to build things like roads or play areas.