Step 1:
Get your child to use his/her 洪荒之力(as much effort) to push against the wall till he perspires. Is he/she doing work?
NO.
Step 2:
Get your child to 不费之力(not much effort) and the chair from one end to the other. Is he/she doing work?
YES.
In the Science language, work is defined as energy done over a distance. My students understood the link when a tangible and physical action is carried out. They get to see, they get to do. They get to understand too!