NAME:……………………………………. CLASS:…………………….. DATE:…………………..

PRACTICAL No.:………….

To determine the resultant of two non-parallel forces by parallelogram and/or triangle method.

This is a group experiment or even a teacher demonstration.

AIMS:

1. To interpret how two force vectors produce a resultant force vector.2. To establish the relationship between equilibrant and resultant. 3. To draw a construction to illustrate this relationship between force vectors, resultant

and equilibrant. 4. To define the term resultant – based upon the findings in this relationship.

INSTRUCTIONS:

1. Pay careful attention during the pre-prac. discussion and take notes so that you are sure about what you have to do when you carry out the investigation.

2. Decide on and write up your action plan to establish the relationship between the two vectors in order to establish the resultant of the vectors.

3. Carry out the investigation, making sure that you take careful note to compensate for friction by finding the average positions for the 2 vectors and the point of origin.

4. Construct the vectors by using either a parallelogram (or triangle) of forces, according to a selected scale, in order to determine the resultant of the 2 force vectors.

5. Compare the value of the resultant with that of the equilibrant.

PROCEDURE:

1. Describe your action plan, including a statement of the problem, the apparatus you will use and the method you will follow.

2. Carry out your investigation, taking the readings and measurements. State clearly how the forces have been kept in equilibrium and how you have compensated for frictional forces, in determining an average position for the force vector positions.

3. Using either the triangle method, or the parallelogram method, construct and measure the value of the resultant force of the two force vectors.

4. Compare the value of the resultant force vector with that of the equilibrant of the two forces.

ASSESSMENT:

Consult the rubrics on the next page to see how your work will be assessed. Ensure you have carried out all the requirements. The total mark for this investigation is indicated on the rubric assessment sheet.

NAME:…………………………………. CLASS:………………. DATE:………………….

Assessment of relationship between non-parallel forces and the resultant of the forces by means of the parallelogram or triangle of forces experiment .

Assessment of group work and skill

CriteriaCompetency level

Not achieved1

Partially achieved2

Achieved3

Learner works co-operatively with others, each having a part to play 1 2 3Performs prac. without needing instruction. Knows what to do & is well prepared.

1 2 3

(6)Assessment of analytical skills

Criteria Competency levelNot achieved

1Partially achieved

2Achieved

3Learner disturbs the equilibrium several times to establish ave. direction for vectors fro origin.

1 2 3

Selects a suitable scale for construction 1 2 3 (6)Assessment of recording skills

Description of competency level Competency levelReadings measured and constructed correctly to scale, in logical manner, demonstrating understanding of process required for analysis of the construction to find the resultant of the two force vectors.

4

Readings recorded in haphazard manner, without logical structure. 3Errors in recording that will negatively influence the outcome of investigation.

2

Clearly no understanding of procedure needing to be followed, to achieve a successful outcome.

1

(4)Assessment of interpretation of data

Calculation criteria Competency levelConstructs correctly and accurately, using correct/suitable scale, thus finding the resultant of the two forces. Shows a distinct positive relationship between resultant and equilibrant for the two force vectors. Able to define a resultant vector from this relationship.

4

One error made in above 3More than one error made in above 2Attempts construction, but no real understanding of procedure 1

(4)

Maximum marks: 20 Marks achieved:…………………….

Sample experimental results:

The diagram below indicates what the experimental setup looks like. As can be seen from the diagram, the cotton OB is attached to an 80 g mass, while OA is

attached to a 70 g mass. The mass attached at the knot O is 100 g. Using a suitable scale, construct a parallelogram (or triangle) for the 2 vectors and

determine the resultant vector for the two. Compare the resultant vector of the 2 vectors with the equilibrant vector of the 2 force

vectors. From your measurements, deductions and conclusions, define a resultant vector. The angle between OB and the vertical is 440, while that between OA and the vertical is

530.