Hands-Off Physics: How to Roll a Can Without Touching It!

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“And now, we are going to make this empty soda can move…without touching it!” Here’s our hidden secret: we’re going to make that can move with static electricity.

This experiment uses a negatively charged balloon to move a neutrally charged empty soda can by using static electricity, attraction and repulsion of charges, and electrostatic induction.

Time to put on your magic hats and get the ball, er, can moving!

How to make the Rolling Can with Static Electricity STEM experiment

Supplies you will need

For this experiment, you will need the following:

Balloon
Empty can

Supplies needed for the Rolling Can with Static Electricity STEM experiment

Before you start

This experiment works best with clean hair.

Instructions

Here is how to do this experiment with your child:

Step 1: Blow up the balloon and tie it off

Blow up your balloon to 3/4 full or full and tie a knot in the neck of the balloon.

Step 2: Charge your balloon

Now the fun part! Start rubbing the balloon on your hair (preferably clean hair). You’ll want to rub the balloon on your hair for about a minute or more, depending on how clean and fine your hair is.

You will know the balloon is carrying a good charge when a lot of your hair gets stuck to the balloon when you lift the balloon.

Step 3: Make the can move!

Place your empty soda can on its side on a flat surface.

Slowly approach the empty can with the charged balloon, but DO NOT TOUCH the can! That’s one of the important lessons from this experiment (electrostatic induction below).

How close to hold the balloon to the can (don’t touch the balloon to the can!)

The STEM behind the Rolling Can with Static Electricity experiment

This experiment teaches:

Static electricity
Attraction and repulsion of charges
Electrostatic induction

How it works

When you rub the balloon on your clean hair, electrons transfer from your hair to the balloon, making the balloon negatively charged in the spot you rubbed on your head. An empty can is initially neutral, which means it has an equal amount of positive and negative charges.

When our charged balloon is brought near the can (without touching it), the balloon’s negative charges repel and essentially push away the free electrons in the can. Those electrons move to the far side of the can, leaving the side closest to the balloon with a net positive charge.

Since opposite charges attract, the negatively charged balloon is attracted to the positively charged side of the can. This attraction pulls the can, causing it to roll towards the balloon (electrostatic induction) and across the table!

Static electricity

This experiment introduces kids to the concept of static electricity, which is the buildup of electric charge on the surface of an object. It helps them understand that certain materials can become charged when rubbed together, like when we charge the balloon with our hair.

We can rub certain materials together to transfer electrons, which creates a net electrical charge on that object.

If your child is a little older and is ready to learn about atoms, you can dive a little deeper into electrons, protons, and neutrons!

We can envision an atom, with the center containing a nucleus. That nucleus contains protons (positive charge) and neutrons (neutral charge). Around the nucleus are electrons (negative charge). Here’s a cool article diving into atoms a little more, including some helpful infographics.

Some materials, like the balloon in our experiment (rubber), have electrons that can easily detach, which make them great conductors of electricity.

When we rub the balloon on our hair, friction causes the electrons to be transferred from your hair to the balloon. That gives the balloon a negative charge! That negative charge creates an electrical imbalance that can interact with our empty soda can in the experiment.

Attraction and repulsion of charges

Now, let’s talk about the attraction and repulsion of charges.

You’ve probably heard that “opposites attract”, right? That’s what is going on in our experiment!

When we rubbed the balloon against our hair, we made the balloon negatively charged. The empty soda can is initially at neutral charge, which means it has an equal number of positive and negative charges.

When you bring a negatively charged balloon (which means it has more electrons) near the neutral can, the electrons in the balloon “push” (exert a repulsive force) on the electrons in the metal can.

The electrons in our empty soda can are free to move around, so the negative charge from the balloon pushes the electrons in the can to the side opposite of the balloon. Those electrons want to be as far away from the negative charge of the balloon!

Once those electrons shift to the side opposite of the balloon, the side closest to the balloon becomes positively charged.

The attraction between the positively-charged side of the can and the negative charge of the balloon pulls the can towards the balloon, and since the soda can can roll freely, that force causes it to roll.

But that’s not all!

As the can continues to roll, the electrons are still redistributing themselves in the can to stay as far away from the balloon as possible. That means the side of the can closest to the balloon continues to be positively charged and the can continues to roll.

This can continue on until the charge from the balloon isn’t strong enough to make the can’s electrons and protons to redistribute.

Electrostatic induction

Don’t let this big name scare you, because it’s as simple as this experiment!

Electrostatic induction is a physics concept that shows how a charged object (like our balloon) can affect a nearby object’s distribution of electric charges without actually touching it.

So, in our experiment, electrostatic induction is how our negatively charged balloon can make the can roll without actually coming into contact with it. The electric field does all the work!