Physics Lab: Negative Energy Loss on Roller-Coaster Track

[bhatnv]

Homework Statement

We recently did a lab in my physics class where we looked at the conservation of energy of a ball on a roller-coaster track.

We got the data as seen in the picture below
http://tinypic.com/r/168zx2s/7

the question now is why is there negative energy loss, is this energy loss neglible or is there a reason for it?

Homework Equations

The Attempt at a Solution

only real thing i could think that could cause this is imprecise data, but i doubt that to be the case

 

[PhanthomJay]

The loss is due to kinetic and rolling friction. On an ideal frictionless track, there would be no loss in mechanical energy (and neither would the ball roll, it would slide). But in the real world, frictionless surfaces do not exist, so there will always be some energy loss due to the work done by friction, such losses showing up mostly as heat and sound energy (energy cannot ever be lost, rather, it is just transformed to different forms). In your case, the loss in mechanical energy is about 5%, which shows up as heat and sound energy, mostly.
Edit: some of the loss may also be due to experimental error

 

[bhatnv]

i understand that part, but my main concern is why is there an increase in energy or in other terms negative energy loss

 

[PhanthomJay]

Oh, I see there are a few instances at the beginning where energy is gained. Ideally, the initial mechanical energy of 0.0999 should be the total energy throughout the trip. Friction, in the general form of heat and sound energy, cause mechanical energy losses, and experimental error (there must be some) can also cause apparent losses. Mechanical energy is gained if energy is added to the system (maybe you blew on it?), or, more likely, it is due to experimental error. Is your data actually accurate to 4 significant figures?