Expanding Ball & Ring- Thermal Expansion

By Arpa Ghazarian

• Principles: A metal ball fits through a hole in a ring. If the ball is heated or the ring is cooled, it does not fit anymore.

• • Keywords: temperature, thermal expansion, coefficient of linear expansion, coefficient of volume expansion

  • History:

    • In the construction of railways, in the building of bridges and houses, account is always taken of the expansion of materials. Because when something gets hotter, it also increases slightly in size. The Leiden professor Willem Jacob 's Gravesande devised this gadget in order to demonstrate the effect to his students. The ball is first heated so that it expands to the point where it no longer fits through the ring. Next the ball is placed on the ring, where it continues to cool until it fits in it again. At that moment the ball suddenly drops down without anyone having given it a helping hand!'s Gravesande's intention was to surprise his students so much that they would never forget the experiment. And he succeeded pretty well, since ''s Gravesande's ball and ring' is still one of the best-known demonstration experiments.

• Standards: Ninth grade

  • • Heat and Thermodynamics

      • 3.Energy cannot be created or destroyed, although in many processes energy is trans­

      • ferred to the environment as heat. As a basis for understanding this concept:

      • a.Students know heat flow and work are two forms of energy transfer between

      • systems.

      • b. Students know that the work done by a heat engine that is working in a cycle is

      • the difference between the heat flow into the engine at high temperature and the

      • heat flow out at a lower temperature (first law of thermodynamics) and that this

      • is an example of the law of conservation of energy.

      • c. Students know the internal energy of an object includes the energy of random

      • motion of the object’s atoms and molecules, often referred to as thermal energy.

      • The greater the temperature of the object, the greater the energy of motion of the

      • atoms and molecules that make up the object.

      • d. Students know that most processes tend to decrease the order of a system over

      • time and that energy levels are eventually distributed uniformly.

      • e. Students know that entropy is a quantity that measures the order or disorder of a

      • system and that this quantity is larger for a more disordered system.

      • f.*Students know the statement “Entropy tends to increase” is a law of statistical

      • probability that governs all closed systems (second law of thermodynamics).

      • g.* Students know how to solve problems involving heat flow, work, and efficiency in

      • a heat engine and know that all real engines lose some heat to their surround­

      • ings.

• Materials:

• • Brass metal ball and ring

  • Bunsen burner

  • Striker

  • Beaker with cold water

• Procedure:

• • Show students that the metal ball easily goes through the ring

  • Turn on Bunsen burner.

  • Hold metal ball above flame and heat for a minute.

  • Try to put the heated metal ball through the ring (won't be able to do it)

  • Put the heated metal ball in the beaker with the cold water

  • Put the cooled metal ball through the ring again (should go in)

• Explanation: Most materials when heated will expand (water being one exception when its temperature is close to zero degrees celcius). If various metals are heated in a bunsen flame then they will expand. Conversely if they are cooled they will contract. If a metal plate containing a hole is heated then the whole plate will expand including the hole. Imagine a circle drawn on the plate with no hole.

• How to use the Demonstration :

  • Ask the students what will happen to a solid when heated (it expands).

  • Ask the students what will happen to a hole when the material surrounding the hole is heated (it also expands).

  • Perform some of the experiments.

  • Hold the ball and ring up to the class and show them that the ball does not pass through the ring.

  • Ask the students how the ball could be made to fit through the ring.

  • Perform the experiment by heating the ring and show that the ball does indeed pass through.

  • Everyday Examples: Railway tracks, Loose phone lines (contracts when weather gets colder so they're hung loosely so that phones lines don't snap), egg in a bottle demonstration, heating a metal lid on a glass bottle in order to remove the lid, thermostat/thermometer, and shrink fitting.

• References: P

  • Thermal Expansion of Common Metals

  • Thermal Expansion Formulas involved

  • Thermal Expansion- Wikipedia

• Other Demonstrations to try:

  • Bimetallic Strip Demo

  • Egg In A Bottle Demo