You could hold any object (like an apple) for your class to see. (Its potential energy is greatest at this point). At the point when you are holding the object the potential energy will be equal to the object's mass multiplied by the object's acceleration due to gravity(9. 8 m/s²) multiplied by the height of the object(however high you choose to hold it). Release the object while it is falling, the object's motion will be evidence of the kinetic energy that the object is experiencing. As the object's kinetic energy increases, its potential energy will decrease. This can be explained by the law of conservation of energy. This law states that energy cannot be created or destroyed it can only change forms. Finally, explain to your class that mechanical energy is the sum of kinetic and potential energy.
I hope this helped. I recommend you present with an informative powerpoint in the background of your presentation while you present this if you want to do well because it will better show your teacher how much you know rather than if you were to just speak to the class during your presentation.
