Simple machines have only one part to do the work and they have very dew or even no moving parts. A lever is an example I can start the class with. Since we will be building a lever with a fulcrum out of Legos later in the activity. You can use a lever to move a larger load with a smaller effort. I will then bring out the Legos and discuss how a small simple machine can be easily constructed out of the Lego set. The only struggle I can see the students having is piecing the parts together to form the correct lever. They will be able to visually see where the load and effort are on the Lego set.
The terms load and effort are used in describing how simple machines work. The load is the object that is moved. The effort is the force used to do the work. In this case, the effort is me pushing down on the Lego lever, and the fulcrum and pivot help move the load up and down. There are three common ways to set up a lever. This activity was a type 1, or, the fulcrum is between the force and the load, or between the input and output.