Must or Have to - roleplay

Some months ago I asked one of my colleagues how she explained the difference between Must and Have to to her students. She gave me a great idea, which I used in class. My fifth-graders enjoyed the activity and asked when we were going to have a cameraman in class.

The  http://www.englishgrammarsecrets.com/musthaveto/menu.php explains the difference as follows:

We  use 'must' to express a strong obligation. When we use 'must' this usually means that some personal circumstance makes the obligation necessary (and the speaker almost certainly agrees with the obligation.)

• I must go to bed earlier.
• They must do something about it.
• You must come and see us some time.
• I must say, I don't think you were very nice to him.

We can also use 'have to' to express a strong obligation. When we use 'have to' this usually means that some external circumstance makes the obligation necessary.

• I have to arrive at work at 9 sharp. My boss is very strict.
• We have to give him our answer today or lose out on the contract.
• You have to pass your exams or the university will not accept you.
• I have to send a report to Head Office every week.

We all see the definitions are clearly presented but not fun to learn.

 I explain to my students that we use MUST when the speaker  imposes a rule or a law, which has been made by himself. This person usually has the authority to impose rules and regulations and it is absolutely obligatory to keep the rule.
We use HAVE TO when the speaker hasn't made the rule himself but renders a rule/law someone else has made.

For example: When their parents tell them they should be back home by 10 p.m. because of the curfew, we use HAVE TO, because the parents only use a rule /law the government has made.
But when their parents tell them they MUST be back home by 9 p.m. then it is the parents' rule.

In the video the following examples are given:

Students must wear uniforms.
Students have to wear uniforms.
1.The class chooses a student to play the role of the headmaster of the school. Then, we choose 3 teachers, because we have 3 rows of desks. (Each row of desks represents a different class. Each of the three teachers is the form teacher of one of the "classes").
2. The headmaster gathers the teachers for a teachers' meeting and tells them, "Students in our school must wear uniforms." This is a rule the headmaster himself has made. He is the authority.
3. After the teachers' meeting  each of the teachers goes to their classes and renders the headmaster's words to the students by saying, "Students in our school have to wear uniforms."

This is my first year of teaching I like explaining modal verbs. What is more, my students think they are nice to learn, too.