We found out that invisible things also exist and can be very powerful, such as the CO₂ produced in the experiment. Matter can be found as solids, liquids, and gases, and it can change state when heated or cooled. Density means how tightly matter is packed, and it was essential because the CO₂, being denser than air, fell onto the candle and stopped the oxygen from reaching it, which made the flame disappear.
Un circuit elèctric és com un camí tancat per on passa el corrent. Si aquest camí es trenca, la bombeta no rep energia i no pot encendre’s. Algunes forces no necessiten contacte perquè existeixen els camps, com el camp magnètic dels imants. Quan apropem dos imants, els pols iguals es repel·leixen i els pols diferents s’atrauen. La brúixola sempre assenyala el nord perquè la Terra té un camp magnètic propi que orienta l’agulla.