The Science Behind It

Why Do BOTH People Move?

It looks like only one person is doing the work.

One person pulls the rope while the other person simply holds on… yet both people roll towards each other!

That happens because forces are a two-way interaction.

When the puller pulls on the rope, the rope pulls back on them. At the same time, the tension in the rope pulls on the person at the other end.

With very little friction stopping the wheels, both people begin to move towards each other.

Newton’s Third Law

Newton discovered something amazing about forces:

Forces always come in pairs.

If one object pushes or pulls on another object, the second object pushes or pulls back with an equal force in the opposite direction.

This is called Newton’s Third Law of Motion.

So when you pull on the rope, you aren't creating a force that acts in only one direction.

There is always another force in the interaction.

But the Holder Wasn’t Pulling!

It certainly looks that way!

The holder isn't deliberately pulling the rope towards themselves. They are just holding on.

But by gripping the rope, they become part of the interaction.

As the rope becomes tight, tension transfers forces between the two people.

So the holder doesn't need to actively pull to experience a force.

That is what makes this experiment such a great trick for your brain!

Try next

• See Newton's First Law — what happens when a force stops acting → [The Runaway Planet]

• Explore how the same force produces very different results depending on mass → [The Coin Heist]