Solids and Elastic potential Energy Exploration Phase What can we use to store mechanical energy? Lab Activity Is there a limit to how much deformation force a solid object can take? Bend a Popsicle stick to through different amounts of stress without breaking it. 1
Now, break the stick. How does this compare to fault formation in rock near the edge of a tectonic plate? Thinking Activity: Consider the lab activity you just performed. From beginning to end, cite all forms of energy the Popsicle stick possessed. Were there any energy conversions taking place during this activity? If so, state these transformations. Are there any energy losses? If so, state their source. Lab Activity: Push the washer along your desk, giving it some speed as it leaves your hand. Then make a mental note as to how far it slid prior to coming to a stop. Vary the speed that the washer leaves your hand and again, make a mental note as to how far it takes for it to stop. Record your observations. Lab Activity: Using scotch tape, tape two washers together which will serve as your puck. Shear a plastic ruler by a small amount, place the puck in front of it, and release the ruler. Make a table of how far the ruler was deformed and how far the puck traveled. Perform three trials of each. Plot your results (average distance traveled versus shear deformation) below. Lab Activity: Cut a straw to five lengths: 1cm, 1.3cm, 1.6cm, 1.9, and 2.2cm. Place the spring in each straw, and compress it as far as possible. Then release it allowing it to push the puck. Make a table of how far the spring was deformed and how far the puck traveled. Perform three trials of each. 2
Plot your results (average distance traveled versus tensile deformation) below. Make a general statement of how the amount of potential energy stored in a solid is related to the amount of deformation of the solid. 3
Concept Introduction Phase Please discuss the results of the activity with your lab partners. Summarize the results in your own words below. Now, describe the results of the activity using some of the following words: energy, mechanical energy, kinetic energy, elastic potential energy, friction, thermal energy. Now we will discuss with the group. Make some notes below. 4
Application Phase Lab Activity Do rocks have elastic properties? One way to observe whether this is the case is to examine coefficient of restitution (COR), defined as the square root of the ratio of the height to which an object bounces over the height from which the object was dropped. Approximating the marble in your kit to rock, drop it on the rock floor and determine its COR. If the COR=1, then the collision is considered perfectly elastic, and no mechanical energy is lost in the collision. Is the collision of two rocks perfectly elastic? Account for all the energy before the collision, during the collision, and after the collision. Lab Activity Now, pull out your materials from the last lesson: eight washers, your homemade spring scale, and the two pieces of sandpaper. Pull the weighteddown small piece of sandpaper slowly with the spring scale until it just begins the slide. Record your observations below. Evaluate the pulled rock in terms of energy stored in the spring and released. A similar effect is seen when masses of rock move along each other along a fault line: they don t move all the time, and when they do move they release huge amounts of energy. This phenomenon is referred to as elastic rebound. Given what you have seen in this activity, explain how the rocks can build up such great amounts of energy in stress and then release it all at once. Why don t the rocks move all the time, causing constant earth quakes? 5
Terms Energy, kinetic energy, potential energy, gravitational, elastic, mechanical, losses, friction, conservation of energy, thermal energy, work, force, and any other words you want to include. 6