EXP: Force, mass and acceleration

Task

Your task is to complete the following experiment and construct a full experimental report according to the attached rubric, against which your work be assessed. Ensure you have all the key sections in your report and tick off the key criteria for each section as you complete them.

This task is part of your assessment for this subject.

Aim

To investigate the effect of mass on acceleration when a constant force is applied.

Equipment

• dynamics trolley (500 g)• pulley• string • 10 x 50 g weights • stopwatch• masking tape • metre ruler

Diagram of experimental set up:

Extra 50 gram masses are placed on the trolley.

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50 g mass

Method

1. On the bench top, use the masking tape and the metre ruler to mark out the starting line for a course for your dynamics trolley, approximately 1 metre from the pulley mounted on the edge of the bench.

2. Tie one end of the string to your trolley. Place the trolley at the starting line and bring the string forward so that it passes over the finish line and then hangs over a pulley at the end of the bench.

3. Hold the trolley in place and tie the 50 g mass to this end of the string. Measure and record the distance from the bottom of the 50 g mass to the ground – this is the distance of the course.

4. Place 450 g on the trolley. Start the stopwatch at the same moment the trolley is released and time how long it takes for the weight to hit the floor. Enter the time in the data table.

5. Repeat this step a minimum of two more times. (Three trials that are within 0.2 seconds of each other are required.)

6. Repeat the experiment for extra loads on the trolley between 450 g and 0 g.

Results processing:

7. Find the average time for the three trials for each mass.

8. To evaluate the acceleration from the time, use the following formula to determine the average acceleration for each different mass:

a = 2d/t2, where d=distance (m) of the course (which is the same as the distance from the hanging weight from floor) and t is the average time (s).

9. Plot a scatter graph of average acceleration of the trolley versus total mass of the trolley.

Results table

The results table will be emailed to you. Enter your times and distance and the spreadsheet will calculate the rest. It will look like this:

mass(kg) cart time trials time(s)

masses+ hanging mass 1 2 3 average height(m)accel m/s/s ma (N)

1.000 1.42 1.38 1.49 1.43 0.912 0.892 0.8920.950 0.900 0.850 0.800 0.750 0.700 0.650

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0.600 0.550

Points to include in your discussion

Discussion Point 1: Explain how your results relate to motion and forces theory.

Discussion Point 2: In the final column of your results table is the experimentally determined value for the net force acting on the trolley. Evaluate the force of the driving mass (thrust) using F = mg (where g is 9.80 N/kg). Comment on how this compares to the experimentally determined net force and explain any difference.

Discussion Point 3: State if the experimentally determined net force is constant or if it changes with the total mass of the trolley. Does this agree with what you would expect? Explain your results.

Final points

Please use the rubric carefully and be sure to include all sections in your report including the evaluation.

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Experiment: Newton’s Second Law Name: Design Comments

A1 Title and Intro 2 1 0 Introduction - gives relevant background Science (without answering the aim) Introduction - Includes relevant formulae, scientific explanations and/or theories

and shows an understanding of how the experiment relates to these concepts.A2 Aim and Hypothesis 1 0 Hypothesis – relevant prediction has been provided

A3 Materials 3 2 1 0 Provide a detailed list of the materials used (eg. 2x 250ml beakers) Include a labelled diagram of the experimental set-up

A4 Variables and reliability 3 2 1 0 Independent variable – include units Dependent variable – include units Controlled variables – explain how you ensured specific variables were controlled

A5 Method 3 2 1 0 Process involved has been clearly outlined Indicate how you will use your data (eg. find the average) Written in third person, past tense in numbered steps

Data collection and processing Comments

B1 Results: Data collection 3 2 1 0

Data recorded – three trials within 0.2 seconds for each mass are recorded Data recorded – sufficient number of different masses are trialled Title – appropriate title provided for table

B2Results: Data processing and presentation

5 4 3 2 1 0

Calculations – calculations for processed data clearly shown or explained; consistent number of decimal places with raw data

Graph selection – correct choice of graph selected; trend line provided if needed Accuracy – IV/DV in correct positions; data plotted appropriately Titles/units – appropriate title provided for graph; headings provided on both

axes, with units Presentation/scale – correct presentation; accurate scales used on both axes

Conclusion and evaluation Comments

C1 Discussion 6 5 4 3 2 1 0

Description of results – detailed summary of results provided Identification of trends – general trend of data or correlation between variables

has been discussed Identify anomalies – any unexpected results or highly varied data have been

discussed Discussion point 1 (see prac sheet) Discussion point 2 (see prac sheet) Discussion point 3 (see prac sheet)

C2 Evaluation 4 3 2 1 0

Discussion of reliability/validity of data – consider the impact of anomalies and variation in your results

Evaluate procedure – Did your method allow you to collect accurate and reliable data? If not, explain why.

Evaluate equipment – Are you using the best equipment? If not, explain why. Suggested improvements – Suggest ways to increase the reliability, accuracy and

range of data collected

C3 Conclusion 3 2 1 0

Reference to the aim clearly made - what have you determined? Was your hypothesis/prediction supported? How confident can you be with your conclusion based upon the limitations/

measurement technique you used? Does it agree with the expected scientific theory?

Teamwork and Safety Scientific Literacy Comments1 0 2 1 0

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[Marks will be deducted for late submissions.]Total

35

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