ExploreLearning News : Science

Expert Corner: Equilibria Everywhere

Kurt Rosenkrantz is a science curriculum writer and Gizmo designer for ExploreLearning. Kurt holds a Master of Science in Geology from the University of Cincinnati, and a bachelor's degree in Earth Science from Harvard. He taught high school and middle school science for eight years before joining ExploreLearning in 2005.

In much of life we seek to balance opposing forces: money earned vs. money spent, weight gained vs. weight lost, heat vs. cold. When opposing forces are perfectly balanced, the system is said to be in equilibrium and no overall change is observed. For example, if you spend exactly as much as you earn, your total amount of wealth won't change.

The concept of equilibrium plays a prominent role in every field of science: from the delicate balance of Earth's climate to the forces that keep a satellite in orbit. A simple example of equilibrium occurs when an object is hung from a spring, as shown in the Determining a Spring Constant Gizmo. The force of the spring pulling upward increases as the spring is stretched, while the pull of gravity on the object is constant. Eventually the spring is stretched enough that the spring force is exactly equal to the weight of the object. At this point the spring force and gravitational force are in equilibrium and the object remains in place.

When a system in equilibrium is perturbed, the system will often oscillate, or swing back and forth from one state to another. Oscillations can be seen when you pull down a spring or release a pendulum, as illustrated in the Simple Harmonic Motion Gizmo.

A similar oscillation can occur in the populations of predators and prey in isolated environments, such as the classic case of the wolves and moose of Isle Royale, shown at left. As predator populations rise, prey populations are depleted until the predator population crashes. With fewer predators, prey populations recover and the cycle begins again. These oscillations are illustrated beautifully in the Food Chain Gizmo.

Recently we published two new Gizmos which directly address the topic in the field of chemistry: Equilibrium and Concentration and Equilibrium and Pressure. Both Gizmos explore reversible chemical reactions. In a reversible reaction, the rates of the forward and reverse reactions depend on the concentrations of reactants and products. As the forward reaction proceeds, the concentration of products increases. This causes the rate of the reverse reaction to increase as the forward reaction slows. In the Gizmos, you can measure the rate of each reaction by observing the blue flashes (representing the forward reaction) and red flashes (representing the reverse reaction) over time. As equilibrium is approached, the rates of each reaction become approximately equal.

See how many examples of equilibrium you can find in your class!

Michael Mosby: ExploreLearning Educator of the Month

Michael Mosby is in his fifth year of teaching and he now teaches 4th grade science at Owens Elementary, in Cypress-Fairbanks ISD, Texas.

He recently attended a Gizmos training event and was excited to take advantage of them in his classroom. He now uses many different Gizmos, covering concepts as diverse as Density and Phases of the Moon. At an ExploreLearning School Leadership event last spring he was honored for his extensive use of Gizmos, bringing more engaging and effective math and science instruction to his students.

Mr. Mosby points to the Density Gizmo as a good example of how Gizmos have helped with his teaching. He uses a hands-on experiment to explore density with his class and then reinforces that lesson with the Gizmo. He has his students pair up and work through the Exploration Guide to go over the various concepts. This sequence has really engaged his students, and this difficult concept has become easier to teach and fun for students.

Mr. Mosby doesn't stop with classroom instruction either.

"I encourage my students to use Gizmos at home with their families. The students really enjoy showing their parents the things that they get to do on Gizmos at home. I think it gets them excited about science concepts that they would normally not be interested in."