Aim

To analyse the effect of three concurrent forces acting at a point when no movement results.

Hypothesis

Three concurrent forces in equilibrium acting on a single point have a sum of zero.

Equipment

string, 3 spring balances (with scales in newtons*) with similar scale ranges, A3 paper

* if the scales are in grams or kilograms use the approximate conversion 10 N = 1 kg (force)

Procedure

1.  Tie one end of three pieces of string about a metre long together and tie a loop at the other end of each piece of string.

2.  Connect a spring balance to each loop and pull the strings taught in a horizontal plane. Ensure that the strings are not at 120° to each other.

3.  Place a sheet of A3 paper under the strings so that the point where they are tied together is approximately in the centre of the sheet. Mark this point on the paper.

4.  Ensuring that the strings do not move, mark where each string crosses the edge of the paper.

5.  Record the stretching force (called the tension) present in each string next to the corresponding mark at the edge of the paper from the reading on the spring balance.

Analysis

1.  Choose a suitable scale and draw a vector arrow representing each force from the central point in the direction of each force (i.e. towards each corresponding mark you made on the edge of the paper).

2.  Add the three force vectors together using the tip-to-tail method.

3.  Draw in and measure the resultant force vector (the resultant is the sum of the forces) if it is non-zero. The resultant force is the vector drawn from the beginning of the first vector to the tip of the last vector added. The sum is independent of the order in which the vectors are added.

Conclusion

£  State whether the sum of the forces determined from measurements in your investigation is consistent with the hypothesis.

£  State whether the sum of the forces determined from measurements in your investigation is consistent with your observations made during the investigation at the time the data was recorded and justify your statement.

In any first-hand investigation you must be able to do the following:

1.  Clarify the aim or purpose of the investigation
2.  Identify all equipment and resources used to conduct the investigation
3.  Describe the correct use of all equipment and resources
4.  Discuss the control of variables in the investigation (controlled, independent, dependent)
5.  Recount the steps followed in the investigation
6.  Explain how validity and reliability were achieved / 7.  Assess and minimise risks inherent in the investigation
8.  Record data and results in tables and graphs (remember headings, labels, quantities, units)
9.  Analyse data (may involve drawing line of best fit, finding averages, comparing results, equations)
10.  Make a conclusion in terms of the aim of the investigation
11.  Apply the principles / results of the investigation to real-world examples.

Can you do each of these things for this investigation?

A student recorded the following results. Analyse these as per the procedure detailed for this first-hand investigation in lieu of your having results of your own.