Final answer:
Rubbing your hands together to warm them does work on the outside world, but the efficiency of this activity is low.
Step-by-step explanation:
When you rub your hands together to warm them, you are indeed doing work on the outside world. This is because rubbing your hands together involves applying a force over a distance. The efficiency of this activity, however, is low. This is because a significant portion of the work done is converted into other forms of energy, such as sound or heat, rather than directly warming your hands.
An example of this is when you rub your hands together rapidly, you may hear a sound or feel them getting warmer. The sound you hear is energy being transferred to the air as sound waves, while the warmth you feel is energy being transferred to your hands and surroundings as heat.