Electric Charge

Remember the tipsy tape pieces? What happened when both pieces of tape were stuck to the same surface then brought close to each other? the tape pieces moved away from each other. What is the scientific word for this action? repel – write this in your notebook

Remember the moving tape pieces? What happened when one piece of tape was stuck to the table then the other piece of tape was stuck on top? the tape pieces moved toward each other. What is the scientific word for this action? attract– write this in your notebook

What the heck?! What you created with the straws and tape is an “electroscope” – a device that detects electrical charge. An electroscope used in a testing lab might look like this:

How does an electroscope work? When the little metal leaves inside the glass both have the same electric charge, they repel each other and move apart. When the leaves have opposite charges they attract and move back toward each other.

What’s going on with the tape? When you rip a piece of tape off the table, there is a tug-of-war for electric charges between tape and table. The tape either steals negative charges (electrons) from the surface or leaves some of its own negative charges behind, depending on what the surface is made of.

Understanding tape atoms By the way, which subatomic particle inside of an atom has a negative charge? Can you remember from Elementary School? an electron has a negative charge (write this down)

Understanding tape atoms It is always the electrons that jump from one object to another, because protons and neutrons are much too big to move. What charge do protons have? Positive (write this down) What charge do neutrons have? No charge (write this down)

What’s going on with the tape? Back to the whacky tape… When you pull two pieces of tape off the same surface, both pieces of tape end up with the same kind of charge, either positive or negative.

What’s going on with the tape? Since like charges repel, the pieces of tape move away from each other.

What’s going on with the tape? When the tape sandwich is pulled apart, one piece rips electrons away from the other. The piece that gained electrons now becomes negatively charged. The piece that lost electrons now becomes positively charged.

What’s going on with the tape? Since opposite charges attract, the two pieces of tape move toward each other.

What’s going on with the comb? When you rub a comb on wool (or any type of hair) the comb grabs extra electrons from the hair and becomes negatively charged.

What’s going on with the comb? If a piece of tape is repelled by the comb, the tape must have the same charge as the comb. (they are both negative) If a piece of tape is attracted to the comb, the tape must have the opposite, positive charge. (since the comb has a negative charge)

Label the charges according to your observations Object Charge Evidence / Observations Plastic Comb Negative Tape A _______ Repelled by tape B. Repelled by comb. Tape B Repelled by tape A. Repelled by comb. Tape C Attracted to tape D. Repelled by comb. Tape D Attracted to tape C. Attracted to comb. Tape - Plastic _____________ by comb. Tape - Aluminum Tape - Cotton

What type of observations are these? Object Evidence / Observations Tape A Repelled by tape B. Repelled by comb. Tape B Repelled by tape A. Repelled by comb. Tape C Attracted to tape D. Repelled by comb. Tape D Attracted to tape C. Attracted to comb.

Materials act differently… If you rubbed silk fabric onto a rubber stopper, what charge would you expect the silk to have? silk = lose electrons = positive What charge would you expect the rubber stopper to have? rubber = gain electrons = negative

Without touching The balloon can attract or repel without touching each other. Same as the comb and the tape. Electric forces can act “at a distance”. (write this down) These balloons are both negatively charged, so they repel each other even though they don’t touch.

Now test your understanding, while standing If the response is positive, cross your arms to form a plus sign If the response is negative, place your arms on top of each other to form a minus sign. If the response is neutral, place your arms to your sides, to indicate nothing.

Stand on your chairs – ready go! An atom gains extra electrons so it is now _____________ charged. An atom is just chillin’ so it is ________________. An atom loses electrons so it is now _______________ charged. A object is attracted by a negatively charged comb, so it must be ____________ charged. An object is repelled by a positively charged piece of fur, so it must be ____________ charged. An atom is part of a human resting in bed, so it is probably _________. An atom is part of a human who has rubbed her feet on the carpet, so now it has gained electrons and become __________ charged.

A quick summary – (draw this in your notes) Two opposite charges will attract Two positive charges will repel Two negative charges will repel The force of attraction or repulsion between charged particles is called ELECTRIC FORCE

How do we know? You can shock someone with electric force by touching them after building up charge by shuffling. Socks stick to shirts after tumbling in the dryer. Electric force between opposite charges holds them together. What evidence can you observe which proves that an electric force is there, even if you can’t see it? Think for a minute, then write an answer on your mini-white board.

A video explanation from Bill… Click on the picture to launch video

What is Static Electricity? The word “static” means that the electrons stay still, and do not move. (unlike current electricity, where electrons move in a circle) Static Electricity is the build up of electric charge on an object (write this down) Charges build up when negative electrons are transferred from one object to another.

Click on the picture to launch video In your notes, draw a model which explains why the cereal jumps to the record, then back down. Make a 3-pane cartoon.

Click on the picture to launch video In your notes, draw a model which explains why the baby’s hair stands on end after going down the slide. Make a 3-pane cartoon. Click on the picture to launch video

Exit Ticket: Draw a model that shows how this magic trick might work. (Try this at home tonight and amaze your family!) Click on picture to launch video

If you were absent: A video explanation of Electric Charge Click on the picture to launch the video