Investigation #2 The Energy of Position Investigating GravitationalPotential Energy Investigating Gravitational Potential Energy

Can a penny dropped from the top of the Empire State Building have enough energy to crack the concrete sidewalk? What would you need to know to answer this question? How fast would the penny be moving when it reaches the ground? How much force would it take to crack concrete? What other forces could influence the outcome?

Energy is defined by change... 8 th Grade Energy Investigations

Investigating Falling Objects Drop the ball onto the motion detector from 4 different heights. What is the “change” that is being measured? Focus Question: How does an object’s drop height (and its GPE) affect its speed as it falls?

What patterns did you observe in the data?

Investigation Questions: Observe the graph. Are the lines for all of the trials the same? How are they similar? How are they different? Which trial produced the greatest speed? What happens to the final speed of the ball as we increase the height of the drop? What does this tell you about the object’s KE? Between which two drop heights does the speed change the most? Between which two drop heights does the speed change the least?

Energy Diagrams & Energy Chains Using Graphical Representations to Communicate the Energy Flow in a System.

Energy Diagrams Energy Chains are used to illustrate the flow of energy in a system. Energy Diagrams show the flow of energy in a small piece of an energy chain. The energy diagram is also much more quantitative.

Energy Diagrams Let’s use a skidding car as our example.

Using Font Size The size of the font can signal the relative amount of energy in a specific form and how it changes over time.

Using Bar Graphs Bar graphs can show how energy flows in a system. Each bar represents a form of energy. The height of the bar signals the amount of energy at that time. In some cases a standard bar graph is used, but a composite bar graph can be used to illustrate the flow of energy.

Standard Bar Graph

Composite Bar Graph

Using Circle Graphs Circle graphs can be used to illustrate energy flow. Each form is a represented by a portion of the circle. Multiple circle graphs can illustrate how the amount of energy in each form changes over time.

Circle Graph

Constructing Energy Diagrams Construct Energy Diagrams for the Falling Ball Investigation

Energy Diagram using Font Size changes 100cm 75 cm 50 cm 25 cm 0 cm GPE KE Total ME

Energy Diagram using a Bar Graph 100 cm 75 cm 50 cm 25 cm 0 cm GPEKE

Energy Diagram using a Composite Bar Graph 100 cm 75 cm 50 cm 25 cm 0 cm GPEKE

Energy Diagram using a Circle Graph 100 cm 75 cm 50 cm 25 cm 0 cm GPEKE

Energy Skate Park Simulation

Quantifying GPE … Forces transfer energy, so what was the force that transferred energy to the ball (in the form of GPE)?

What causes weight? Isn’t weight the same thing as mass? How can you quantify weight?

Question #1: When we raise the ball off of the ground, we say that it has GPE. Where did that energy come from? Question #2: What force was involved in lifting the object? How can we find the amount of force needed to lift the object? Question #3: What was the distance traveled during this lifting process? Question #4: How could we quantify the energy transferred to the ball during the lifting process? How can we determine how much energy was transferred to the ball during the lifting process?

GPE = mass x gravity x height = mgh So can the penny crack concrete if it is dropped from the top of the Empire State Building? As the GPE transforms into KE, the speed at which the penny strikes the sidewalk should be about 200 miles per hour!

A discrepancy in the data? When tested, the falling speed of the penny was only about 65 miles per hour. What happened? Where did the energy go?

Investigating Air Resistance 1.Drop a “wadded” coffee filter onto the motion detector. 2.Drop an “unwadded” coffee filter onto the motion detector. Which trial experienced more air resistance? Focus Question: How does air resistance affect the speed and KE of a falling object?

Investigation Reflection: Observe the graphs. How are they similar? How are they different? What is the purpose of dropping the “coffee filter ball”? What is the force acting on the coffee filter that changes the way it falls? What are the maximum speed values for each trial?

Which trial produced the greatest speed? Explain why this trial produced the greatest speed. Which trial produced the smallest speed? Explain why this trial produced the smallest speed. How much slower was this trial from the fastest trial? If the GPE is not being converted to KE, as we can see from the graph since the speed is not increasing as much in the normal coffee filter trial, where is the energy going? Why did the falling penny that fell from the Empire State Building only reach 65 mi/hr? Where did that energy go?

Power … So far in the investigation we have examined distance and were reluctant to discuss time. The time that it takes to transfer energy is also important. Power is the rate at which energy is transferred or transformed.

As an equation … Power = Energy Transferred Time

Who’s Got The Power? You will be timed as you run up a set of steps. You will then used this data to calculate your power. Focus Question: How can power be quantified?

MassGPETimePower DATA TABLE:

Investigation Reflection: 1.Create an energy chain for this activity. Think about the forms of energy that were involved and the energy transfers/transformations that occurred during the activity. 2.Did everyone transfer the same amount of energy? Why/why not? 3.If two people complete the climb in the same amount of time, do they use the same amount of power? Why/Why not?

4.Could two people use the same amount of power if they complete the climb in different amounts of time? Why/Why not? 5.If you want to dry your hair quickly, should you select a 1200 watt dryer or a 1600 watt dryer? Why? 6.If the hair is dried completely by either dryer, which one will use more electricity and cause a higher bill? Why?

Summary Write a brief summary of this investigation in your journal. In the introduction of this investigation two friends, Luke and Sam, are debating whether or not a falling penny from the Empire State Building could crack the concrete. Do you think this idea could be plausible or is it just a myth? Write a response to this question after your summary. Include an energy diagram of the falling penny. How much energy does the penny have at any point? How could you quantify its energy? Are there other factors that would need to be investigated? How would they factor into the actual outcome?