Relating Graphs, Position and Speed (no time graphs)
for Conservation of Energy
http://phet.colorado.edu
Learning Goals: Students will be able to:
1. Describe Energy -Pie, -Bar, and -Position Charts from position or selected speeds.
a. Explain how changing the Skater affects the situations above.
b. Explain how changing the surface friction affects the situations above.
2. Predict position or estimate of speed from Energy -Pie, -Bar, and -Position Charts
3. Look at the position of an object and use the Energy -Pie, -Bar, and -Position charts to predict direction of travel or change in speed.
1. Josie made a frictionless hot wheel track that looks like the one shown. She placed a red rubber ball on the left top of track at 1.
a. Make a data table like the one below
b. Fill in the Prediction column by sketching what you think the Pie chart will look like for the ball at points 1-4.
c. Use the Loop Track with the Ball Skater to test your ideas and make any adjustments
Link: http://phet.colorado.edu/sims/energy-skate-park/energy-skate-park_en.jnlp
Pie chartPrediction / Simulation / Explain differences
1 / All potential energy / All potential energy / none
2 / Mostly kinetic energy, slight amount of potential energy / Mostly kinetic energy, less than ¼ potential energy
3 / Very little kinetic energy and lots of potential / Less than ¼ kinetic energy, mostly potential
4 / About half potential energy and half kinetic energy / More kinetic energy than potential energy / Height is relatively low and kinetic energy is higher due to high ramp that the skater just came off of
2. Pretend that Josie can magically change the ball to different things like the simulation can.
a. What do you think would change about the Pie Charts?
The pie charts would be larger and the kinetic energy would be much greater than the potential energy because of the increased speed of the ball, but the potential energy would still actually be the same.
b. Explain why you think the charts would similar or different.
The ball would go faster with the magic options and so the kinetic energy would be greater generally throughout the simulation. There would be a greater ratio of kinetic energy to potential energy.
c. Check your reasoning using the simulation and make corrections if necessary.
Our predictions and reasoning was correct.
3. Josie has a friend, Phillip that can magically change the friction on the track like the simulation can.
a. What do you think would change about the Pie Charts?
The potential energy would appear greater than the kinetic energy.
b. Explain why you think the charts would similar or different.
The friction would slow down the skater so there would be less kinetic energy in the system.
c. Check your reasoning using the simulation and make corrections if necessary.
We were generally correct with our predictions.
4. Work with your partner to build a track and sketch it.
a. Make a table like the one you did for question 1.
Prediction / Sim / Reasoning for Differences1 / High potential energy with no kinetic energy / High potential energy with no kinetic energy
2 / High kinetic energy with little potential energy / High kinetic, little potential
3 / High kinetic with some potential / High kinetic, some potential
4 / High kinetic, low potential / High kinetic, low potential
b. Predict what you think the charts will look like.
c. Use the simulation to check your ideas.
d. Test your ideas from questions 2 and 3. Make changes to your answers if necessary.
5. Explain how you can use what you understand about pie charts to predict bar charts.
Larger slices of the pie chart would create taller bars on a bar graph.
6. Sketch this track and label where the 5 spots could be.
a. He is at his maximum speed
Point 2
b. He is stopped
Point 1 and 5
c. He is going his average speed
Point 3
d. He is going slow
Between 2 and 3 and Points 4 and 5
e. He is going fast
B
f.
Between 1 and 2 and points 3 and 4
7. Sketch this energy-position graph and label where you think the same 5 spots are.
a. Test your ideas using the Double Well Roller Coaster track.
b. If one of your friends in the class asked you for help making sense of this type of graph, what would you say?
Notice that total energy stays constant, just as in the pie graph. The kinetic and potential energy add up to the same thing no matter where you are on the graph. Reading the kinetic energy will tell you the speed and the potential energy will tell you the height.
8. Talk about how you could use the Energy -Pie, -Bar, and -Position charts to predict direction of the ball is rolling.
If the kinetic energy is greater than the potential energy, the ball is rolling toward the left. If the potential energy is greater than the kinetic energy, the ball is rolling toward the right.
a. Check your ideas using the simulation.
b. Talk about how you could tell if the ball is going to be moving faster, the same, or slower.
The kinetic energy will tell how fast the ball will be rolling.
c. Pretend you are writing a test for this unit.
Type a question that includes at least one type of graph and a Skater on a different track.
Then, give it to another group to see if they can predict the direction and changing speed of the ball.
Make sure to attach your question.
2/3/2011 Loeblein http://phet.colorado.edu