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Investigation #4

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Investigation #4

Stretching the Limits

Investigating Elastic Energy & Earthquakes

- Different sizes
- Different materials
- Different uses

Energy is all around us. Sometimes it is stored in elastic materials as Elastic Potential Energy (EPE)

1) What makes some materials better able to store EPE?

2) How do materials store EPE?

3) Are all materials elastic? Do elastic materials always stay elastic?

- The energy stored in the temporary change in shape of an object
- EPE is Stored Energy
- EPE is a source of mechanical energy

Elastic means:

Ability to regain its original shape after change

- To transfer EPE requires application of forces
- This force physically moves the particles of objects closer or farther apart
- but still preserves the connections between particles

- EPE Energy is stored within the connections between particles, all particles
- The more stress placed on the connections, the more energy stored

What happens when the force is removed?

- EPE stored is converted to KE of the particles

What happens when the force is too much…

- The connections break
- EPE energy stored in the parts is converted to KE
- By 2nd law, parts accelerate

- Since the object can no longer go back to its original form, object is not longer elastic in nature

Elastic Forces & EPE

What are elastic properties and how do they help predict how an elastic material will behave?

Investigating Elastic Materials

Focus Question: How are elastic forces and their stretch related?

Use the force probe to explore the relationship between the elastic force and the stretch distance for several elastic materials.

Be sure to click on the KEEP icon each time you collect a data point!

- Record force and distance data for 3 elastic objects
- Create a graph the relates forces (N) to distance stretched (m)
- All points on one graph

- When scientists interpret their data after an investigation, they look for patterns that emerge. What patterns emerge from your data?
- The slope of the line in a linear graph tells the reader about the relationship between the dependent variable (the force) and the independent variable (the stretch distance).
Are the slope values the same for all trials? If they are different, what may have caused any differences you observe? Are these differences significant? Explain.

- Predict the force needed to extend each spring 2 cm farther than your last data point for each object. On what do you base this prediction?

- Predict the force needed to extend each spring 20 cm farther than your last data point. On what do you base this prediction?
- Which of the above predictions (3,5) do you think is more likely to be accurate? Explain.
- What are the limitations of this procedure that may affect the accuracy of your data?

1: Which object stretched had the steepest slope?

2: Which object took less force to stretch 2 cm?

- The slope of line connecting force to distance stretched defined as elastic constant (k) (units = N/m)
- F = kx

- The elastic constant can be different for every elastic material.
- Higher the k value, the tougher it is to stretch the object

3: Why don’t all of the lines of best fit intersect the origin?

4: When an object is compressed energy is stored.

Stored where?

- When an elastic material is stretched or compressed, a force is applied to transfer energy to that material.
- Energy is stored within the connections between particles

5: Using the line of best fit, how would you determine the amount of force needed to stretch a rubberband 5 cm? 25 cm? 100 cm?

6: which of those answers is the least reliable?

Why?

- All elastic materials have an elastic limit, which is the point at which the material no longer will return to its original shape and no longer behaves like an elastic material.

- rocks can compress or stretch along a fault line only so far before that they “readjust”

EPE & Distance

How are the EPE and the distance that an elastic material is stretched or compressed related?

- Does it take the same force to stretch a rubber band at all times?
- The greater the distance stretched, the greater the energy transferred

Relationship between Force applied and distance stretched is LINEAR

F = kx

Relationship between EPE and distance in not simple (linear)

This relationship is commonly stated using the equation EPE = ½ kx2.

k =

X =

- If a spring has an elastic constant of 1300 N/m. How much EPE does it possess if it is stretched 43 cm?
2) How much force does it take to press a finger into your skin 1.2 cm if it has a elastic constant of 8 N/m? How much energy does your skin have when pressed?

EPE & Earthquakes

How does EPE relate to the study of earthquakes?

- Every year approximately 3,000,000 earthquakes occur worldwide. 98% percent of them are less than a magnitude 3.
- Fewer than 20 earthquakes occur each year, that are considered major (7.0 – 7.9) or great (8 and greater).
- Between 2000 and 2009, the United States experienced approximately 32,000 earthquakes; 6 were considered major and occurred in either Alaska or California

- The largest event in Delaware occurred in 1871 and had an estimated magnitude 4.1.
- The largest recorded event in Delaware occurred in 1973 and had an estimated magnitude of 3.8.
- The last recorded earthquake in De was recorded on July 1st, 2009 with an estimated magnitude of 2.8.

- Depends on how close event is to the monitor device (seismometer)
- Trains, Trucks, Animals, people
- Farther away, quarry explosions, road work

- Delaware, unlike CA and Alaska, is not near a tectonic plate boundary
- Tectonic plates flex, under pressure

- In earthquakes, a lot of EPE is turned into KE
- Think about how many objects move as a result of the earthquake
- During the 1906 earthquake, the earth moved up to 20 feet in seconds

- Does all of the rocks EPE transform into KE?
- If not where does it go?

- Seismic waves that travel around the world through the earth

- Melting, bending of rock at plate boundaries
- Serpentine Rock

- A small amount may be converted into sound that reaches the atmosphere

Investigating Earthquakes

Focus Question: How are elastic forces and their stretch related?

Your task is to explore how earthquakes occur because of a transformation of EPE to KE by using a model.

- Pressure builds up, Rock changes shape, EPE increases, Rock held by friction
- Friction overcome, Rock moves to release built up energy, earthquake occurs
- Cycle repeats itself

- Be sure to address the following questions and use your data to support your responses.
- Is the relationship between stretch/compression and EPE linear or not?
- What is meant by the terms “elastic constant” and “elastic limit”?
- Where does the EPE go after an earthquake (an energy chain or an energy diagram may help in answering this question)?