When two steel spheres are smashed together, enough heat is generated at the point of contact to burn a hole in a piece of ordinary paper! How can this possibly happen? I can guarantee one thing, it ain't magic!
There is no such thing as magic. Or is there? How can two metal spheres burn through paper? Not sure. Check it out.
In this experiment kinetic energy is converted into thermal energy, or heat, which causes the paper to burn at the place of contact. Some energy from the balls’ motion is also converted into sound waves as the spheres collide, which results in the loud crack you and your students hear.
The energy in the system (spheres and paper) is initially in the form of kinetic energy, or the energy of motion. In this case the kinetic energy is in the form of translational motion, since the entire sphere is moving toward the paper. Kinetic motion can also be vibrational, as in molecules vibrating within a material, or rotational, like when a wheel spins around its own center while the entire wheel does not change its position.
When the two spheres collide they stop, which means they no longer have translational kinetic energy. This energy must go somewhere because energy is conserved overall. Some of the energy from the collision is converted to thermal energy, or heat. This heat changes the temperature of the paper and warms it enough to burn a small hole. The rest of the energy creates sound waves, which we hear as a crack. Some energy may also remain in the balls and cause them to vibrate when they collide.
The smashing spheres are just one example of conversion from one form of energy to another. To extend the concept of conservation of energy farther you may wish to discuss where the energy one partner used to move the spheres came from. The food chain can be used to illustrate that our energy comes from food, while the energy in our food comes from plants and ultimately from the Sun.
Here is one example of how you might use these spheres in class. They can be found at about any science supply company online.
Source: Achieve Inc. 2013
Check out more explanations and extensions!
Have cool science demonstrations you show your classes regularly? Save time and materials by making a quick video tutorial of your own for students. By using demonstrations and lab investigations regularly, students not only will know science, they can apply it!
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