BACKGROUND INFORMATION
The more friction between the marble and the track, the less efficient the marble-track system. The more energy the marble uses to overcome friction, the less it has to make it up the hill.
The amount of energy retained by the marble during its trip can be found by determining the ratio of h2 to h1. This ratio of h2 to h1 is the "efficiency" of the marble-track system. For example, a frictionless system would be 100% efficient. and a 70 % efficient system would lose 30% of its potential energy to frictional forces.
Potential energy is determined by mulitplying mass x gravity x starting height. In this experiment, mass and gravity are constant. Thus, only the heights need to be compared.
efficiency = Potential Energy at Point B/ Potential Energy at Point A =(mxgxh2)/(mxgxh1) = h2/h1
Notice mass and gravity cancel each other out.
The loss of energy = 100% - efficiency.
ANSWERS TO #6-8
6. Data analysis: (Describe your data and results.)
When the initial height decreased, so did the final height decrease. The efficiency of my roller coaster track ( increased, stayed the same, decreased , zigzagged up and down) as the initial height was reduced. The average efficiency of our coaster was __________.
7. Conclusion: (Why did you get these results?)
Friction is a force that opposed the motion of the marble rolling along the track. In order for the marble to roll, it must overcome friction. Even though the marble is very smooth, the track is not. The irregular texture of the coaster slowed down the marble.
8. Other Questions
a. Why was it necessary to keep the track from moving sideways?
Movement of the track would introduce other forces (variables) into our marble-roller coaster system. It would affect our results. If it moved, we could not say that friction was the only force that slowed down the marble.
Conservation of Momentum: energy is neither created nor destroyed
b. Examine the data table. Is h2 ever greater than h1? Explain why or why not?
No. (The amount of potential energy of the system equals mass x gravity x starting height. The mass of the marble and the gravity of the earth stayed the same throughout the experiment. The only thing that changed is the starting height.)
Thus, the starting height determined how much potential energy the marble can have. The only way the marble could go higher is if it got more energy from another source.
c. If the marble-track system were frictionless, how far up the track would the marble travel?
If frictionless, the marble would travel up the other side equal to the initial height.
d. If the track is 80% efficient, where does the other 20% of the energy go?
Air resistance, Friction and heat (even though there is not much heat in this particular experiment - rub your hands together to feel how friction causes heat)
If the roller coaster had no friction at all, its efficiency would be 100%. Efficiency tells you how good an enegy saver a roller coaster is. Ours ( was, was not) very efficient.
e. What factors would influence the amount of friction experienced by the marble-track system?