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Home Concept Builders Static Electricity Getting the Hang of Charge Video Video Transcript

Video Transcript: Getting the Hang of Charge

We provide the transcript below to those who for whatever reason would find the written words to be preferred over in addition to the actual video.

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Charged objects interact with other objects in their surroundings. By observing these interactions, you can often predict the type of charge an object possesses. To do so, apply three simple rules of charge interactions:
First, like-charged objects repel each other.
Second, oppositely-charged objects attract each other.
And third, any charged object, whether + or -, and a neutral object will attract each other.

Notice that "attract each other" appears twice on our list. So if two objects are attracting each other, there are two possible explanations: either they are both charged with opposite charge types – one positive, the other negative. Or one of the objects is charged and the other is neutral. More observations are required to determine which explanation applies.
Let's mix "rules" 1, 2, and 3 with some logical reasoning to do four examples.

Example 1: We know balloon X is + and balloons X and Y repel. Balloons Y and Z also repel. What is the charge on balloons Y and Z? Like charges repel (Rule 1). So if X is + then Y must be +. Since Y and Z repel, they too must be like-charged (Rule 1). So Z is also +.

Example 2: We know X is + and X and Y attract. Opposites attact (Rule 2) so Y could be –. But a charged and neutral also attract (Rule 3), so Y could also be neutral. But then we observe that Y and Z repel. Only charged objects repel (Rule 1) so Y can't be neutral. Y is – so Z is also –.

Example 3: We know X is + and X and Y attract. So Y is either – (Rule 2) or neutral (Rule 3). Balloons Y and Z also attract but we have limited knowledge about Y. If Y is -, then Z could be + (Rule 2) or neutral (Rule 3). But Y could also be neutral; and Z would attract a neutral if it were + or – (Rule 3).

Example 4: We know X is + and X and Y attract. Balloons Y and Z also attract. And balloon Y attracts neutral paper bits. There are three Y observations. Y's interactions with paper bits indicates Y is charged. Since Y and X attract, we know Y is – (Rule 2). Finally, since Y and Z attract, Z is either + (Rule 2) or neutral (Rule 3).

These four examples illustrate how logic and three simple rules about charge interactions allow you to predict the charges on objects. I'm Mr. H, letting you know that … You got this!

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