Grade by Grade
C. Matter and Energy · Electrical Phenomena, Energy, and Devices

Static Electricity: Charges That Build Up

C2.1 A1.2 A1.4 A1.5About 45 minutes
Learning goals
  • I can explain that everything is made of atoms with positive and negative charges.
  • I can explain how rubbing two materials together moves electrons and charges them.
  • I can use the rules "like charges repel" and "opposite charges attract" to explain what I see.
  • I can explain everyday static electricity, like shocks from a doorknob, clinging clothes and lightning.

Words to know

atom
One of the tiny particles that everything is made of. Atoms are far too small to see.
proton
A tiny particle in the centre of an atom that has a positive (+) charge. Protons stay put.
electron
A tiny particle on the outside of an atom that has a negative (−) charge. Electrons can move from one object to another.
neutral
Having the same number of positive and negative charges, so there is no overall charge.
static electricity
Electric charge that builds up on the surface of an object and stays there until it can escape.
repel
To push away.
attract
To pull toward.
discharge
When built-up charge suddenly moves off an object, sometimes as a spark.
electrostatic
To do with static electricity (electric charges that are not flowing).

Crackle, cling, ZAP!

It's a cold, dry January morning. You pull your wool toque off and your hair stands straight up. Your fleece crackles when you take it off. Then you shuffle across the carpet in your socks, reach for the metal doorknob and... zap!

All of these are caused by static electricity. In this unit you will explore electricity: static electricity, the electricity that flows through wires, how circuits work, where our electricity comes from, and how to use it wisely.

Remember from Grade 3

In Grade 3 you learned that static electricity is a non-contact force. You rubbed a balloon on your hair and saw it pull (attract) some things and push (repel) others without touching them. You also learned that lightning is a giant spark of static electricity.

In Grade 6 you will find out why this happens, using tiny particles called electrons.

A bright bolt of lightning flashes from dark storm clouds over a wide lake at dusk.
Lightning is a giant spark of static electricity. Charges build up in storm clouds until they jump through the air all at once. AI-generated image

What everything is made of

  • Everything around you is made of tiny particles called atoms.
  • In the centre of each atom are protons. Protons have a positive (+) charge. They stay where they are.
  • Around the outside of the atom are electrons. Electrons have a negative (−) charge. Some electrons can be rubbed off one object and onto another.
  • Most objects have the same number of positive and negative charges. They balance out, so the object is neutral (no overall charge).

How objects get charged

When you rub two different materials together, some electrons move from one material to the other.

  • The object that gains extra electrons now has more negative than positive charge. It is negatively charged (−).
  • The object that loses electrons now has more positive than negative charge. It is positively charged (+).

When you rub a balloon on your hair, electrons move from your hair onto the balloon. The balloon becomes negative and your hair becomes positive.

This is called static electricity because the charge stays put (static means "not moving") on the surface. It builds up best on materials like rubber, plastic, wool and hair, because electrons don't move easily through them.

Before rubbingAfter rubbing++++−−−−++++−−−−balloon: neutralhair: neutral4 +, 4 −4 +, 4 −++++−−−−−−++++−−2 electronsballoon: NEGATIVEhair: POSITIVE4 +, 6 − (extra electrons)4 +, 2 −Only the electrons (−) move. The + charges stay put.
Rubbing moves electrons from the hair to the balloon. The balloon ends up with extra electrons (negative), and the hair is left with fewer electrons than + charges (positive).

The rules of charges

  1. Like charges repel. Two negative objects push each other away. Two positive objects push each other away.
  2. Opposite charges attract. A negative object and a positive object pull toward each other.
  3. A charged object attracts a neutral object. A charged balloon can pull on tiny bits of paper, or stick to a wall, even though the paper and the wall have no overall charge. The balloon's charge nudges the electrons in the nearby surface, so the side closest to the balloon ends up with the opposite charge, and opposites attract.
−−−−−+++++opposites attractsweaterballoon−−−−−−−−like charges repel
Left: a balloon rubbed on a wool sweater has extra electrons (−). The sweater lost electrons (+). Opposite charges attract. Right: two balloons rubbed the same way are both negative (−), so they push each other apart. Like charges repel.

Discharge: when the charge escapes

Built-up charge doesn't stay forever. When a charged object comes close to something that lets charge move easily, like metal or the ground, the charge can suddenly jump. This is called a discharge.

  • The doorknob zap. As you shuffle across a carpet in socks, your body picks up extra charge. When your hand gets close to a metal doorknob, the charge jumps across the tiny gap as a spark. You feel it as a shock.
  • Lightning. Inside a thunderstorm cloud, ice and water bits crash together and charges separate. The bottom of the cloud usually becomes negative. When enough charge builds up, it jumps to the ground or another cloud as a huge spark: lightning. Lightning heats the air so fast that it expands with a boom: thunder.
  • Lightning rods. A metal rod on top of a tall building gives lightning a safe path down a thick wire into the ground, instead of through the building.

Static is worse in winter. Damp air helps charge leak away slowly. Cold winter air, and heated air indoors, is very dry, so charge builds up more and you get more shocks.

What you noticeWhy it happens
Your hair stands up after you pull off a toqueYour hair loses electrons to the toque. Each hair is now positive. Like charges repel, so the hairs push away from each other.
Socks cling together straight out of the dryerThe clothes rub as they tumble. Some gain electrons and some lose them. Opposite charges attract.
A rubbed balloon sticks to the wallA charged object attracts a neutral one.
A zap when you touch a doorknobCharge built up on your body jumps to the metal: a discharge.
You hear crackles taking off a fleece in the dark (and might see tiny sparks)Tiny discharges as charges jump between the fabric and you.
Lightning during a summer stormA giant discharge between a charged cloud and the ground (or another cloud).
Everyday electrostatic events and the science behind them.
Worked example

Let's explain the balloon and the hair

Amira rubs a balloon on her hair. When she lifts the balloon away slowly, her hair rises up toward it. Explain what happened, using charges.

  1. Before rubbing, the balloon and the hair are both neutral: equal positive and negative charges.
  2. Rubbing moves some electrons from Amira's hair onto the balloon.
  3. Now the balloon has extra electrons: it is negative (−). The hair lost electrons: it is positive (+).
  4. Opposite charges attract, so the positive hair is pulled toward the negative balloon.
  5. Bonus: the hairs are all positive, so they also repel each other and spread apart.

Electrons moved from the hair to the balloon. The negative balloon and the positive hair attract each other, so the hair rises toward the balloon.

Just for fun

Two atoms bump into each other. One says, "Oh no, I think I lost an electron!"

The other asks, "Are you sure?"

"Yes, I'm positive!"

Hands-on activity

Balloon investigation: does more rubbing mean more charge?

You need: a balloon (blown up and tied), a wool sweater or your own clean, dry hair, a sheet of tissue paper or newspaper torn into about 30 bits the size of your fingernail, a tap, and an empty pop can.

Part 1: Explore (A1.2)

  1. Rub the balloon on your hair or the sweater for 10 seconds. Hold it near the paper bits. What happens?
  2. Turn on the tap so a thin, steady stream of water comes out. Rub the balloon again and bring it close to the stream (don't touch). Watch the water bend toward the balloon.
  3. Lay the empty can on its side on a smooth table. Hold the charged balloon close to it, without touching. Can you make the can roll?

Part 2: A fair test (A1.2)

  1. Question: Does rubbing the balloon more times pick up more paper bits?
  2. Predict what will happen.
  3. Spread the paper bits on the table. Rub the balloon 5 times in one direction, hold it 2 cm above the bits for 3 seconds, then count how many bits stick. Put them back.
  4. Before each test, touch the balloon all over to a metal tap or pipe, or wipe it with a damp cloth and let it dry, so it starts with no charge.
  5. Repeat with 10 rubs and 20 rubs. Do each test 3 times. Keep everything else the same: same balloon, same material, same height.
  6. Record your results in a table and find the average for each number of rubs.

Share it (A1.5): write a sentence that explains your results using the words electrons, negative and attract.

What to look for: usually more rubs pick up more bits, up to a point. Your explanation should say more rubbing moves more electrons onto the balloon, so it has more charge to attract the neutral paper.

Safety (A1.4): balloons and broken balloon pieces are a choking hazard. Keep them away from babies and young children and throw away any burst pieces right away. Skip balloons if anyone at home has a latex allergy (a plastic comb works instead). Keep the water test away from any plugged-in devices.

Electrons are the movers

When something gets charged by rubbing, it is always the electrons (−) that move. The protons (+) stay in place. So an object becomes positive by losing electrons, not by gaining protons.

Your turn

1

What charge does an electron have? What charge does a proton have?

2

What does it mean when an object is neutral?

3

Which particles move from one object to another when you rub them together?

4

Two balloons are both rubbed on a wool sweater. They hang near each other on strings. What happens? Why?

5

Why do you sometimes get a shock when you touch a metal doorknob in winter?

6

Why does static electricity happen more often in winter?

7

What is lightning?

More practice: warm-up

1

True or false: opposite charges attract.

2

True or false: two negative objects pull toward each other.

3

What does static mean?

4

A balloon gains extra electrons. Is it now positive or negative?

5

Name a place where you have noticed static electricity at home.

More practice: on your own

1

Your hair loses electrons to a plastic comb. What charge does the comb have? What charge does your hair have?

2

A charged comb picks up tiny bits of paper, but the paper has no charge. How is this possible?

3

Why does a metal rod on top of a tall building help protect it from lightning?

4

Why do clothes cling together after the dryer, but not after hanging on a clothesline?

5

After rubbing a balloon, Leo touches it all over to a metal tap. Now it won't pick up paper. Explain.

Challenge

1

Ben rubs balloon A on his hair and hangs it up. He rubs balloon B on his hair too. Then he brings his hair close to balloon A. Predict what balloon B and Ben's hair will each do to balloon A, and explain.

2

In Amira's balloon test she got these averages: 5 rubs → 4 bits, 10 rubs → 9 bits, 20 rubs → 15 bits. Write a conclusion and give one reason her results might not be perfect.

3

Mia says, "Static electricity is when protons jump from one object to another." Correct her statement and explain how an object becomes positive.

Check your understanding

Quiz

1.

Which particle has a negative charge and can move from one object to another?

2.

A balloon rubbed on hair becomes negative. This means the balloon...

3.

Two objects that both have a positive charge will...

4.

A charged balloon sticks to a neutral wall because...

5.

Lightning is an example of...

6.

Static shocks happen more often in winter because the air is...

For parents and teachers

Big idea (C2.1): explain everyday electrostatic phenomena using the principles of static electricity: objects are made of atoms with positive protons and negative electrons; rubbing transfers electrons; like charges repel, opposite charges attract, and charged objects attract neutral ones; built-up charge can discharge as a spark. The fair test practises scientific experimentation (A1.2), safety (A1.4) and communicating with science vocabulary (A1.5).

How to help: on a dry winter day, notice static together (dryer laundry, toques, the trampoline) and ask your child to explain it using the words electrons, attract and repel. Help them keep their balloon test fair: same balloon, same number of rubs per trial, and remove the charge between trials.

Common difficulties:

  • Thinking protons move. Only electrons move when objects are rubbed; objects become positive by losing electrons.
  • Thinking only charged objects can be attracted. Charged objects also attract neutral ones (paper bits, a wall, a stream of water).
  • Mixing up which object becomes which charge. For balloon-on-hair, the balloon becomes negative and the hair positive.

Safety: balloons and burst balloon pieces are a choking hazard for young children; check for latex allergies. Static electricity from balloons is harmless, but it is not the same as electricity from wall outlets, which is dangerous. During thunderstorms, go indoors ("When thunder roars, go indoors").