1. Past Class Exit Slip
You said: “Electric Forces can repel and attract. Gravitational forces only attract.”
What about mass?
What about the size of the charges?
What about distance between the two objects?

2. Coulomb’s Law (1785) Fe = kq1q2/r2 where k = 9 x 109 Nm2/C2
Remember Fg = Gm1m2/r2 (1687) where g = 6.67 x Nm2/kg2

3. Charge is conserved.
Electrons are transferred.
Like charges repel; opposite charges attract.
Electrical forces can act at a distance.
Charge is quantized.
Conductors are materials that electrons move through easily.
Insulators are materials whose electrons are bound more tightly so they are not free to move.
Charging by friction, conduction, induction, polarization.

4. How have we charged objects?
When any two materials in the table are rubbed together, the one that has a higher electron affinity can be expected to pull electrons from the material that is lower. As such, the materials highest on the table will have the greatest tendency to acquire the negative charge. Those below it would become positively charged.

6. Induction:
The charged object is never touched to the object being charged by induction.
The charged object does not transfer electrons to or receive electrons from the object being charged.
The charged object serves to polarize the object being charged.
The object being charged is touched by a ground; electrons are transferred between the ground and the object being charged (either into the object or out of it).
The object being charged ultimately receives a charge that is opposite that of the charged object that is used to polarize it.

7. An electroscope is an instrument for detecting the presence of static electricity. It consists of two thin metal leaves suspended from a metal hook. When the hook is brought near a source of static electricity, some of the electrons in the hook are pushed to the leaves (if the source is negative) or pulled up to the hook from the leaves (if the source is positive). Either way, the leaves are now charged the same way as each other and so they repel each other. The amount they open up is proportional to the charge of the source (if the sources are always held at the same distance from the hook).