The energy we used to do work come from the food we eat. Without eating, the body can not have energy to perform work, that is why we normally do not have much strength when we are hungry.
The food we eat is converted to energy through biochemical processes. The food that we consume has potential energy which is stored in form of chemical energy. In the body, the energy can be converted to heat energy to supply warmth or it can be converted into kinetic energy to perform work.
To be able to do laboratory activity, the chemical energy stored in your cells because of the food you eat will be converted to kinetic energy to perform work.
