Homework from last class:• Read Ch. 7.1 (pp. 248-254)• Complete the Charge It worksheet

•Have you ever stuck a balloon to the wall after rubbing it on your head?

•Has your sweater ever made crackling noises when you took it off?

•Have you ever gotten an electric shock off your door knob?

•Have you ever seen lightning?

All these things happen because of

Static Electricity!

Chapter 7 pp. 248-254

Ch. 7.1 Static Charge

What is Static Charge?Static charge (aka static electricity): an electric charge

that can be collected and fixed in one place• ‘static’ means stationary or not moving

Static electricity occurs when there is a build up of electric charge on the surface of a material.

ex: Objects rub against one another and transfer charge

p. 248

Positive and Negative ChargeAll matter is made of atoms• The centre consists of protons (positively charged) and

neutrons (no charge)• Surrounding the nucleus are electrons (negatively

charged)

p. 250

electron

proton

neutron

Positive and Negative ChargeThe movement, or transfer, of electrons from one atom to another changes the charge on the atom.

• When electrons (-) are gained, the object becomes negative.

• When electrons (-) are lost, the object becomes positive.

Electrons are most often transferred through friction, when objects rub against each other.

p. 250

The Amazing Balloon Static

Demo!

+

++

++ +

+

++

+- -

-

-

-

-

- --

-

+

++

++ +

+

++

+- -

-

-

-

-

- --

-

+

++

++ +

+

++

+- -

-

-

-

-

- --

-

+

++

++ +

+

++

+- -

-

-

-

-

- --

-

+

++

++ +

+

++

+- -

-

-

-

-

- --

-

++

++ ++- -

-

-

-

-

- --

-

+

+++

Balloon Static Demo - Conclusion• The head and balloon each started off with the same number of positive and negative electrons, but the rubbing transferred electrons from the head onto the balloon.Result: Balloon = negatively charged (-)

Head = positively charged (+)

• The positively charged hairs are attracted to the negatively charged balloon, so the hair stands up.

• The imbalance of positive and negative charges causes:

▫ Balloons to stick to walls.▫Hair to stand on end when you brush your hair on a dry day.▫ The electric shock you sometimes get from the door handle.

Insulators and ConductorsElectrical insulators: materials that do not allow

electrons to move easily (Ex: glass, plastics, ceramics, and dry wood)

Electrical conductors: materials that allow electrons to travel freely (Ex: metals)

Only insulators are good at retaining static charge.

Coulomb (C): the unit of electric charge

Charges on insulator

Charges on conductor

p. 252

Generating Static ChargeVan de Graaff generators (VDG): a device that uses

friction to produce a large static charge on a metal dome.

As a rapidly moving belt moves over rollers, contact between the two results in a transfer of charge.

A moving belt produces static charge on a metal dome • The charge resulting on the dome depends on the materials used in the VDG belt and rollers.

p. 253

19

Applications of Static ChargeEx: electrostatic filters can be used to clean air, paint automobiles, and hold objects with electrostatic attraction.

Dangers of Static ChargeEx: Built up static charge can discharge and cause serious shocks, explosions or fires (such as trucks that carry fuel)Pumping flammables must ensure objects are grounded (connected to the Earth so that static charge is discharged).

p. 253-254

Lightning rods protect buildings in

the event of lightning by conducting

lightning strikes through a

grounded wire.

Time for everyone’s favourite scientist….Bill Nye!

Homework for next class:• Complete the “Conductors and Insulators”

worksheet

• Answer Check Your Understanding questions on p. 257: Qs 1, 4, 5, 11, 13, 14, 15

• Study for on time Ch. 7.1 quiz next class

• Read over class notes and check class bloghttp://www.msoonscience.blogspot.com

Have a great weekend!

Works CitedImages taken from the following sources:http://instant-art.com/store/index.php?main_page=product_info&cPath=1_84_87&products_id=7060http://sdsta.k12.sd.us/SDAAPT/2007PhotoResults.htmhttp://www.dak.com/reviews/3306story.cfmhttp://jcooltech.webs.com/apps/photos/photo?photoid=100384418http://startswithabang.com/?paged=8http://www.chemistryland.com/CHM151W/10-LiquidsAndSolids/Chapter10.htmlhttp://www.rfcafe.com/references/electrical/NEETS%20Modules/NEETS-Module-01-

1-1-1-10.htmhttp://www.cartuningcentral.com/how-to-paint-a-carhttp://www.flickr.com/photos/ax2groin/566654614/http://www.cartoonstock.com/directory/s/static_electricity_gifts.asphttp://www.wpclipart.com/household/outdoor/lightning_rod.png.htmlhttp://www.tvrage.com/shows/id-2806