Experiment: Adding forces

In your design task, two cables will share the load of a loud speaker system, and they will be at an angle to the vertical. You will need to be able to work out what the load is in each cable under these conditions.

This experiment will help you understand what the question is. In it you will measure the forces in simulated cables like this.

The analysis videos will help you to provide the answer. The answer is how you can predict these forces in advance.

These two chains of rubber bands meet at a point. How do they share the load? We’ll find out in this experiment and then in the analysis videos. Let’s get started.

We’ll suspend one of our calibrated rubber band transducers from the beam with a loop of string. Then we will suspend the second transducer from the beam with a string like this, wrapping it around the beam so we can vary its length. We’ll connect the lower ends of the transducers together, and suspend a calibrated weight pan from the join. Next, we’ll slide the string along the beam and adjust the variable length until we get a good looking configuration. This looks about right. Next, we’ll load the pan with our steel washers until we get deflection that we can conveniently measure.

For this test, 50 washers should do it. We’ll record the weight of the pan in washer units, the number of washers added, and the extended length of each transducer. We’ll also measure and record the total length of each side of the triangle formed by the transducers and the beam. And we’ll measure and record the height from the top of the beam to the connection point like this. The data we got are given in the data sheet.

Now, we are done for the time being. But we will need the transducers and weight pans from later experiments, and the beam and chairs. So if you are doing the experiments yourself, don’t throw them away.