Some materials have a strong hold on their electrons while others do not. Materials with a weak hold will lose electrons and gain a positive static charge when rubbed with a different material that has a greater electron affinity. Thus, when you brush a plastic comb through your hair, the hair has a lower electron affinity that the comb, meaning the comb will develop a negative net static charge. Placing the negatively charged comb close to a running stream of water causes it to bend away from the comb. Within the covalent bond between oxygen and hydrogen atoms, the oxygen has a stronger pull on the shared electrons compared to the hydrogen. This results in the oxygen having the electrons slightly closer to its nucleus than to the hydrogen nucleus, giving it a slightly negative charge and the hydrogen atoms a slightly positive charge. When placing a negatively charged comb near a stream of water, the water molecules quickly realign so that the slightly positive oxygen faces the negative comb, thereby creating a static repulsion atmosphere. Thus, the water steam from the tap bends away from the comb by means of such dynamics.
These pictures are included in the Art of Physics travelling exposition. To get more information on how your institution can host the travelling exposition, please contact Francine Ford, CAP's Executive Director at cap@uottawa.ca.
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