If more than one force acts on an object along a straight line, then the forces will reinforce or cancel one another depending on their direction and magnitude.
Heat consists of random motion and the vibrations of atoms, molecules, and ions.
Above Standards from the National Science Education Standards . Do not fill it completely full. Fill the balloon until it is just buoyant. Mylar balloons work for this activity because they do not stretch, as do rubber balloons. Do not use rubber balloons.