PHYS4A/ Fall 2014; Unknown Magnet Energy

Purpose: For this experiment we are using a magnet in conjunction with a slider on an air track to determine an equation for the magnetic potential energy.

To set up the experiment, we used an air track attached to a reverse vacuum thus creating an airflow through many small holes throughout the track. By having air flow, we were able to set a metal slider on top so that it could move along the track without friction. By moving the slider towards a magnet on one end of the air track, we were able to see a repelling force when the slider and magnet were close enough. This was due to a magnet also set on the slider of an opposite polarity. In order to get the most accurate results, the track was made to be level so that there was no sliding due to gravity. And the motion sensor was set up on the end opposite the magnet to measure displacement of the slider.

Running the experiment with a small force on the slider.

Elevating the track using wooden blocks and books

Once the track was level, we measured the initial height of the track in order to establish an origin. Once this height was recorded, the track was elevated to a small angle so that the slider would now move due to gravity. Using Newton's Second Law, we were able to create a force equation of mgsin(theta)=ma. By creating a force column and measuring the distance between the two magnets at the end, we were able to plot a force vs separation graph. By taking a power fit of this graph, an equation y=Ar^B is used. This equation was equivalent to a magnetic potential energy function.

The slider at the end of the track in front of the magnet.

 Using this equation, we could calculate the magnetic potential energy. By using this to create a calculated column for energy done, we could create several other columns for energy. By calculating total energy before the slider moves, we were able to equate that to final energy after each run. Kinetic energy was (1/2)mv^2 which could be calculated from data from loggerpro. Using the inital potential energy and kinetic energy which was equal to total energy of the system and equating that to final magnetic potential energy, we were able to see if we had calculated the correct potential energy and show that energy is conserved. The graphs shown do have some fluctuation but that can be due to unaccounted friction that may have occurred. Total energy was around 0.012J.

Bottom graph showing the measured energy levels according to the formulas we input. Top graph shows a total energy which is mostly constant.