Discovery question

What is electricity?

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Use a model to picture static electric charges.

 This is a close repeat of the previous activity. How to deal with this?

Engage

Electric charges are everywhere. They are very small - even smaller than atoms! - so you can't see them. There are two kinds of electric charge, called positive and negative .

Every object has a HUGE number of both kinds of charge. If the number of positive and negative charges is equal, they cancel each other out and the object is electrically neutral. But the object can have more positive than negative charges, or more negative than positive charges. Then it becomes either positive or negative.

You can't create electric charges out of nothing. But when you rub a balloon on wool, positive charges collect on the balloon and negative charges collect on the wool. Then you can observe the force between them.

Draw a balloon and a wool sweater. Using the Stamp tool, put 10 signs and 10 signs on the balloon. Also put 10 signs and 10 signs on the wool sweater.

 DRAWING TOOL - with and stamps available. what size is best?
 help with using the stamp tool.

Is the balloon electrically charged, or is it electrically neutral?

• positively charged
• negatively charged
• neutral

Why do you think so?

Now drag some charges from the wool to the balloon. This is what happens when you rub them together.

Now is the balloon electrically charged, or is it electrically neutral?

• positively charged
• negatively charged
• neutral

Why do you think so?

Explore

Here is a model with a balloon and a wool sweater. It shows positive and negative charges on each object. To start with, the charges are paired up. Each object has equal numbers of positive and negative charges.

Use the mouse to drag the balloon and move it up and down over the wool. What happens?

Now add another balloon by checking the Two Balloons box. Drag the second balloon up and down over the wool. What happens?

When you let the balloons go, they move. Describe what they do.

Now hide the wool sweater by unchecking the Show sweater box. Move the balloons around and let them go. How do they move now?

Explain

When you rub a balloon on wool, some negative charges move from the wool to the balloon. Circle the right words to make these statements true.

The wool becomes (negatively / positively) charged.
One balloon becomes (negatively / positively) charged.
The other ballon becomes (negatively / positively) charged.

Elaborate

 show the model again? preset it with the sweater not visible?

Reset the model. Uncheck the show sweater box. Try rubbing the two balloons together. What happens?

Move the two balloons near to each other. What happens?

If the balloons don't attract or repel each other, what can you conclude?

• One is positive and one is negative.
• Both are negative.
• both are neutral.

Evaluate

Based on your observations of the model, answer these questions with TRUE or FALSE.

Positive charges attract (pull toward) each other.
T F
Positive charges repel (push away from) each other.
T F
Positive charges attract negative charges.
T F
Positive charges repel negative charges.
T F

 Document generated by Confluence on Jan 27, 2014 16:49