2. What is Static Electricity?
Static electricity is an imbalance of positive and negative charges on an object.
Charges on Objects
An object may be positively charged, negatively charged, or neutral.
An object becomes charged when electrons are either removed from or added to the object.

3. - - - Neutral object + number of protons = number of electrons +
Positively charged object
number of protons > number of electrons + -
Negatively charged object
number of electrons > number of protons

4. Law of Electric Charges
A charged object exerts an electric force on a nearby object.
The force either attracts or repels the nearby object.
The Law of Electric Charges states that:
opposite charges attract each other
objects with like charges repel each other
charged objects will attract neutral objects

5. Detecting the Charge on an Object: Electroscopes
An electroscope is a device that is used to detect the presence of electric charges.
There are two types of electroscopes:
pith ball electroscope metal-leaf electroscope

6. With an electroscope you can determine if an object is neutral or if the object has a charge on it. You do this by observing what happens when the object is brought close to a neutral electroscope.

7. Pith ball electroscope
This electroscope consists of a small ball made of pith or cork or Styrofoam hanging from a thread.
If object is neutral, the pith ball does not move
If object is positively or negatively charged, the pith ball swings toward object

8. Metal-leaf electroscope
This electroscope consists of a metal ball connected to two thin metal strips.
If object is neutral, the metal leaves hang straight down
If object is positively or negatively charged, the metal leaves spread apart

9. Homework
p471 #3-9