Why doesn't the marble keep going in a circle?

While the marble is moving around the hoop, something is constantly changing its direction.

When the hoop is lifted away, that influence disappears.

Watch carefully: does the marble continue in a curve, or does it travel another way?

Scientists use experiments like this to investigate how objects move when forces change.

Why is the result surprising?

Many people expect the marble to shoot outward when the hoop is removed.

But is that what you observed?

The experiment reveals something interesting about motion that scientists have been investigating for hundreds of years.

What does this have to do with space?

The marble and the planets have something in common.

Planets don't travel through space randomly. Something is constantly affecting their motion and changing their path.

This simple investigation helps us explore one of the biggest questions in astronomy:

What keeps planets moving around the Sun instead of wandering away into space?

Dr Puddledrip's Curiosity Question

If Earth suddenly stopped orbiting the Sun, where do you think it would go?

Draw your prediction before you look it up.

Try next

• See Newton's First Law in action, keeping a coin still while a card flies away → [The Coin Heist]

• Explore what happens when two equal forces act on two people — and both move → [Newton's Question: Who Moves?]