If mentioned, hot air can be discounted since there is not an obvious heat source. Heat must be continuously be added to a hot air balloon to keep it hot. Once choices are narrowed down to H and He, the students are asked to come up with an experiment to tell the difference. Charge and Static Electricity Plastic, acrylic, and glass rods are rubbed with plastic shopping bags, fur, wool and silk to transfer charge. Most matter is made up of atoms with a compact and tiny positively charged nucleus surrounded by a much larger cloud of negatively charged electrons.
Opposite charges attract and like charges repel.
When two materials are rubbed together, odds are that one material will be more likely to pick up extra electrons while the other will be more likely to give up electrons. The object with extra electrons will be charged negative, or minus, while the object that lost electrons will be charged positive, or plus. Black plastic when rubbed by a plastic grocery bag, fur, or wool will become negatively charged, while the plastic grocery bag, fur, or wool will be charged positive. Acrylic or glass when rubbed by silk will become positively charged while the silk will be charged negative. Attraction and repulsion is demonstrated with these materials by suspending one object in a cradle supported by fishing line and making it rotate by bringing another charged object near.