Steel Ball Sparks

Physics:	Energy Transfers
Grade Range:	Elementary School, Middle School, High School
Format:	Hands-on

Students of all ages will love doing this demonstration. Easy to do, and easy to expand on for any grade level, this is one of the most versatile demonstrations we have.

Materials

• Pair of Steel Balls
• Strips of Paper

Safety Precautions

Please read the General Precautions section of the Demonstration Safety page before performing this demonstration.

Demonstration

1. Ask students to hold out one of the paper strips. Show them the two steel balls, and then smash them together with the paper strip between them. There will be a hole burned into the paper!
2. Give the steel balls to the student, and hold out the paper for them. Let them smash the balls on the paper, and a hole will be burned into the paper!
3. Ask them for ideas on why the steel balls can burn holes in the paper. What is happening? Or rather, what is being transferred?

Why This Works

Short Explanation

Energy Transfers are when one form of energy switches to another. Energy transfers are common, and easy to identify once you are familiar with them. The steel balls have Mechanical Energy, or the energy of moving objects and parts. When the balls collide on top of the paper, the mechanical energy is converted into two types: Thermal Energy and Sound Energy. The loud crack is the sound energy being sent through the air, while the burning of the paper is the result of the thermal energy!

Full Explanation

Energy Transfers are when energy switches from one form to another. Keep in mind that energy isn't created or destroyed; it can only be transferred from one form to another. Energy comes in two basic forms:

• Potential Energy: This is stored energy, or the energy within an object. Potential energy comes in four types: Chemical (Energy stored in the bonds), Nuclear (Energy stored in the atoms), Elastic (Energy stored in compressed or stretched systems), and Gravitational (Energy stored in lifted objects)
• Kinetic Energy: This is active energy, or the transferred energy from an object. Kinetic energy comes in four types: Thermal (Energy of heat transfer), Mechanical (Energy of movement), Electromagnetic (Energy of light waves and electron transfer), and Sound (Energy of vibrations in matter)

In this demonstration, the steel balls start with some potential energy. This potential energy is elastic energy from the muscles of the person holding the ball, which also have stored chemical energy in the ATP used as an energy source. When the steel balls are moving, the system has mechanical energy, showing that the potential energy is being converted to kinetic energy. Once they collide, the mechanical energy is converted to thermal energy and sound energy. The sound energy we clearly hear, but the thermal energy is not visible by itself. Rather, the result of the thermal energy is shown, with a small hole being burned into the paper due to the sudden spike in temperature.

For an easier way to see this process in action, refer to the chart below:

Start Point	Energy Type	End Point	Energy Type
Steel balls being held	Elastic (muscles) Chemical (ATP)	Steel balls moving	Mechanical (motion)
Steel balls moving	Mechanical (motion)	Steel balls strike	Thermal (heat) Sound ("crack" produced)
Steel balls strike (on paper)	Thermal (heat) Sound ("crack" produced)	Paper is burned	Chemical (combustion) Thermal (heat)

As an extension on this topic, you can connect this demonstration to entropy. Entropy is the disorder or randomness in a system, and it is a thermodynamic measurement. notably, it is a measurement of how much energy has been converted to heat energy, in a way which makes it unusable in the system. This demonstration can be used to talk about how the initial chemical and elastic energy is converted mostly into thermal energy, with some sound energy.

Additional Information

• This demonstration can be paired well with the Thermal Fan, Potential and Kinetic Hot Wheels, Tyndall's Bar Breaker, and many other energy demonstrations!