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Moving Can. The Challenge: Use the plastic tube and sheet of plastic to move the can without physically touching it. Electrostatics. Chapter 32. Forces. There are four basic kinds of forces: 1) Gravitational 2) Electromagnetic 3) Strong Force 4) Weak Nuclear Force. Forces.

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moving can
Moving Can

The Challenge:

Use the plastic tube and sheet of plastic to move the can without physically touching it.



Chapter 32


There are four basic kinds of forces:

1) Gravitational

2) Electromagnetic

3) Strong Force

4) Weak Nuclear Force


Gravitational forces:

- we’ve discussed already this year

- is dependent on the masses of the two objects

- we feel the effect of it as weight


Electromagnetic forces:

- think about magnets; what do you already know?

- like ends repel

- opposites attract

- it’s the same with positive and negative charges!


The Strong Force:

What’s wrong with this picture?


The Strong Force:

Scientists theorized that since the nucleus of an atom contains only positive charges, there must be some kind of force that only applies to very small particles over very small distances to keep them from repelling each other. So they said, “Let’s call it the strong force.”


Weak Nuclear Force:

- pertains to nuclear decay and we will discuss this one at more length later in the year.


So let’s put them in order from strongest to weakest:

1) Strong force

2) Weak nuclear force

3) Electromagnetic forces

4) Gravitational force

  • An atom consists of charged particles

protons = positive; electrons = negative

  • Objects become charged by the addition or removal of electrons
  • Ion = a charged atom
conservation of charge
Conservation of Charge

Charge is not created out of thin air.

If an object becomes positively charged, it is usually because another becomes negatively charged.

This is conservation of charge.


Charged objects attract or repel each other with electrical forces


Like charges repel.


Opposite charges attract.

coulomb s law
Coulomb’s Law

French physicist Charles Coulomb

Developed the equation for calculating electrical force between charges

Coulomb’s constant:

k = 9 X 109 Nm2/C2

Object A has a positive charge of 9.0 X 10-6 C. Object B, having a positive charge of 4.5 X 10-6 C, is 0.030 m away. Calculate the force on A.

What is the force on B?

electric field lines
Electric Field Lines

From yesterday’s activity, we could tell that force vectors around a charge look something like this:

electric field lines1
Electric Field Lines

This is what the electric field lines look like around positive and negative charges:

electric field lines2
Electric Field Lines

This is how the field lines interact for two opposite charges positioned near each other:

electric field lines3
Electric Field Lines

What would it look like for two similar charges positioned near each other?

electric field lines4
Electric Field Lines

What would it look like if to flat plates were place near each other, one positively charged, the other negatively?


Electrons are free to move within conductors.

Metals are good conductors.


Materials that have electrons tightly bound to their atoms. They are less likely to move around.

Glass and rubber are good insulators

methods of charging
Methods of Charging


* most common

* electrons are being transferred from one material to another

* like scooting your feet on the carpet

methods of charging1
Methods of Charging


* electrons can be transferred from one material to another

* when a charged object comes in contact with a neutral object

methods of charging2
Methods of Charging


* using a charged object to create a charge in two others by separation

methods of charging3
Methods of Charging

Induction with Grounding

* using a charged object to cause a separation of charges in a neutral object and then either removing or adding electrons by putting in contact with the ground

methods of charging4
Methods of Charging

The bottom of a negatively charged cloud induces a positive charge at the surface of the ground below.

This leads to lightning so the cloud discharges.