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Gallery 3

Gravity Well

Balls roll in elliptical pathways around the dish, until they fall into the 'gravity well's' central hole.

How it works

Release one or two balls into the funnel-shaped dish and watch the balls spin around the dish before it disappears down a hole.

Things to try or ask around the exhibit

• Start rolling one ball from the edge of the top rim and another ball from mid-way down the dish. Which ball will roll into the hole first?
• Can you get a ball to roll directly into the hole instead of rolling around the dish?
• Does a ball roll in a circular or elliptically-shaped pathway?
• Where does the ball seem to speed up or slow down?
• Can you start rolling one ball, then release a second ball so it collides with the first ball's path?
• How can we get a ball to roll around the dish for the longest time?
• How can we get a ball to roll into the central hole as quickly as possible?
• What causes the balls to eventually roll into the central hole?
• Does the ball's pathway remind you of how planets orbit in space?

Background

Balls roll around the dish in oval-shaped tracks called elliptical orbits. As a ball rolls downhill, it accelerates, and it gains enough momentum to roll upwards on the other side of the dish. However, friction slows down the ball, until the ball is attracted towards the central hole by gravity.

When a ball starts from a position high on the bowl's rim, the ball has a greater amount of potential energy. Eventually however, friction causes every ball to slow down and fall into the central hole due to gravity.

The study of how planets move in elliptical orbits around the Sun (similar to balls rolling around the dish), has been undertaken for centuries. Planets move slowly when distant from the Sun, then speed up as they approach the Sun due to gravitational attraction. Even today, scientists continue to study how planetary orbits are affected by gravity and Einstein's theory of gravity continues to be studied using data from satellites.

Finding the science in your world

The bowl's shape has been modelled so the rolling balls can mimic the motion of planets orbiting the Sun, or satellites moving around the Earth. When satellites encounter friction, such as air resistance, they lose energy as heat, falling into tighter and tighter orbits, until they fall to Earth.

Planets and asteroids, held by gravity to the Sun, move in space with very little friction and each planet automatically falls into an orbit that balances its own energy.