Inclined Plane

 

Aims

• To develop understanding of motion with constant accleration.
• To practice the procedures for the processing and presentation of data and uncertainties.
• To practice using interface software.

 

Apparatus

This is a fairly straightforward practical to set up using any sort of trolley and track. The timing is done with a photogate which can be connected to a computer or a stand alone timer. The method does not use the possibility for the software to calculate the velocity for them in the hope that by doing it manualy the student will gain greater understanding of the motion.

PASCO Dynamics system

Photogate (plus connection to computer etc.)

 

Common Problems

The most common problem with this practical is that students confuse the distance travelled down the slope with the distance travelled by the card as it passes through the photogate so when they calculate the velocity they divide the distance travelled by the time instead of the card length by time, the resulting graph will then have a negative gradient.

 

Conclusion and Evaluation

This apparatus gives quite consistent results with little radom error however the value for acceleration gained from the graph does not agree with that from the calcuation gsinø. Students will often say that this is due to the errors in their measurements even though their graph looks fine. The reason is that the calculated value doesn't take into account friction. Students often quote friction as a weakness in their method but it isn't, they are measuring the actual acceleration of the trolley including friction, it is the calculated value that is wrong. This introduces the idea of looking at the evidence from their results; the graph looks fine so they should trust that the acceleration was linear and accurate to within the uncertainties of the experiment, if their result doesn't agree with expected then they shouldn't blame "random error".

An interesting extension of this is to send the trolley up the slope instead of down, the friction is now in the same direction as the component of weight down the slope resulting in a larger value for acceleration.