Electrostatics CHARGING BY FRICTION and CONTACT

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RECAP:  What is electric charge?  Where do electric charges come from?  How can we figure out the charge of an object?  What is the difference between an insulator and conductor?

CHARGING BY FRICTION Charging by friction: electric charges can be transferred by a rubbing action or friction Charging by friction: electric charges can be transferred by a rubbing action or friction Electrostatic Series: Electrostatic Series:  used to determine the kind of electric charge produced on each substance when any 2 substances on the list are rubbed together

Electrostatic Series: the substances higher in the list always lose electrons to become +vly charged the substances higher in the list always lose electrons to become +vly charged the substances lower in the list always gain electrons to become –vly charged the substances lower in the list always gain electrons to become –vly charged

Rubbing materials does NOT create electric charges. It just transfers electrons from one material to the other. Where do charges come from?

When a balloon rubs a piece of wool... Where do charges come from? – Electrons are pulled from the wool to the balloon. The balloon has more electrons than usual – – – – – The balloon: – charged, The wool: +charged wool

Charging by Contact Who has ever touched someone and got a shock? Who has ever touched someone and got a shock? The difference between charging by friction and contact is? The difference between charging by friction and contact is?

Scenario Touching a door knob and a shock occurs Touching a door knob and a shock occurs Why does the shock happen? Why does the shock happen? What is wrong with this diagram? What is wrong with this diagram?

Charging by Contact One object is already charged; the other object may or may not be charged. One object is already charged; the other object may or may not be charged. There must be a difference in charge between the 2 objects. There must be a difference in charge between the 2 objects. The 2 objects must either touch, or come close to touching so that the charge can ‘jump’ from one object to another! The 2 objects must either touch, or come close to touching so that the charge can ‘jump’ from one object to another!

Static Electricity in Winter Static Electricity in Winter At what time in the year does there seem to be an increase in the amount of static electricity? At what time in the year does there seem to be an increase in the amount of static electricity? Why is that so? Why is that so? Has to do with the air, cold air is much drier Has to do with the air, cold air is much drier Cold air can hold less water than warm air. Cold air can hold less water than warm air. Dry air is an insulator, so it does not take up electrons easily from our bodies as air molecules rub against our skin. Dry air is an insulator, so it does not take up electrons easily from our bodies as air molecules rub against our skin. Therefore, the charges that build up on our bodies aren’t taken away, so we are more charged. Therefore, the charges that build up on our bodies aren’t taken away, so we are more charged.

Practice:  What is charging by friction? What must happen for this to occur  Which electric charges move?  How can we figure out the charge of an object?  What is charging by contact? What are 2 ways it’s different than charging by friction?

Discharging Electrically Charged Objects Another word to address discharge is to neutralize something. This is A.K.A. getting rid of any excess electrical charges. Another word to address discharge is to neutralize something. This is A.K.A. getting rid of any excess electrical charges. How do we get rid of excess charges? How do we get rid of excess charges?

Discharging Electrically Charged Objects What is Grounding? What is Grounding? When a charged object is connected or grounded to Earth, it shares its charge with the entire Earth. When a charged object is connected or grounded to Earth, it shares its charge with the entire Earth. For the most part, this effectively removes all the excess electrical charge from the object. For the most part, this effectively removes all the excess electrical charge from the object. Can you name some important devices that are grounded? Can you name some important devices that are grounded?

Discharging by Grounding When a charged object is connected or grounded by a conductor to Earth, it shares its charge with the entire Earth. When a charged object is connected or grounded by a conductor to Earth, it shares its charge with the entire Earth. For the most part, this effectively removes all the excess electrical charge from the object. For the most part, this effectively removes all the excess electrical charge from the object.

Discharge at point Grounding an object is not always the best way of getting rid of an electric charge. Grounding an object is not always the best way of getting rid of an electric charge. The shape of conductors can be used. The shape of conductors can be used. Conductors pointed at the ends lose charges rapidly, “discharging at a point” Conductors pointed at the ends lose charges rapidly, “discharging at a point” Planes have a lot of these, why? Planes have a lot of these, why?

Discharging at a Point Smooth spherical shapes retain charges indefinitely; this is because their charges can spread across their surface evenly. Smooth spherical shapes retain charges indefinitely; this is because their charges can spread across their surface evenly. Conductors pointed at the ends lose charges rapidly, because charges at the point (forced close together) will repel each other Conductors pointed at the ends lose charges rapidly, because charges at the point (forced close together) will repel each other

Other Ways to Discharge Objects Over a period of time charged objects can be discharged by simple air exposure. Over a period of time charged objects can be discharged by simple air exposure. On a humid summer day, there is lots of water in the air. On a humid summer day, there is lots of water in the air. Another way is to simple shine a light on it, exposing it to radioactivity. Another way is to simple shine a light on it, exposing it to radioactivity.

LIGHTNING Lightning is a large example of static electricity with a discharge! How does it work?

5 min phenomenen phenomena-video.htm Lightning and the bremuda triangle Lightning safety gov of Can Upward lightning videos.htm Nova – lightning 60min BBC 50 minute version Short video

Practice for the Quiz