Activity: Mini investigation
This activity provides a break from Physics content, instead introducing the idea of a research question. You will use your knowledge of Mechanics to develop a hypothesis and then employ practical skills to design an experiment to test a hypothesis. Acting as a "detective" you will develop your skills in evaluating results - all the while practising writing a formal report.
In this activity you will perform an experiment related to a small bow and arrow made from a piece of plastic from an ice cream carton and a drinking straw. The bow is used for firing arrows so most experiments will probably be about the projectile motion how ever you could do a static experiment measuring forces. The first stage is to make the bow and arrow and play with it.
As with almost all of the labs you have done up to this point, the data should be displayed as a graph. If possible this should be a straight line graph so you need to manipulate the data so that it is in the form y = Ax + B. Here are some examples:
What should you plot to give a linear relationship between the two variables in each of the following cases:
- s = 1/2 at2 (constant a, relationship between s and t)
- v2 = 2as (constant a, relationship between v and s)
- T = 2π√(L/g) (relationship between T and L)
- v = 2Lf (constant v, relationship between L and f)
It's not always possible to linearise the data for example if u does not equal 0 you can't linearise s = ut + 1/2 at2 but you can plot a parabola.
- If possible manipulate your data so that you can plot a straight line, you have to know the equation relating the data to be able to do this.
- Calculate the uncertainties in you manipulated data using the usual (max - min)/2 method.
The report can be split into sections.
Introduction
Introduce the bow and arrow, what is it made of etc. A photo is a good idea.
Research question
State it clearly, list your variables.
Theory
Use your knowledge of physics to derive a relationship.
State any assumptions.
It doesn't matter if it turns out to be wrong but the physics should be applied correctly. Deviations between theory and practice are often due to incorrect assumptions.
Make a prediction (hypothesis) based on the theory.
Method
What you measured and how you measured it.
How were controlled variables controlled?
Results
This will be in the form of a table.
Don't forget uncertainties (these must be explained).
Follow the same procedure as in other practicals you have done.
Analysis
Manipulate your data in a spreadsheet and propagate the uncertainties.
Graph
Plotted with LoggerPro
Linear if possible but if a curve try to fit the best curve according to your theory.
Conclusion
What did you find out.
Try to justify your findings
Evaluation
Why do your results not exactly match the theory (they never will). Is it because of the theory doesn't apply or was it because of experimental errors?
Discussion
What could you have done better?
If you compared with a simulation write about that here.
Anything else you noticed.