The Formula That Predicts the Future? Master Hooke’s Law and See Like a Scientist!
I’m Ken Kuwako, your Science Trainer. Every day is an experiment.
This time, let’s take a look at an experiment on Hooke’s law and how to carry it out. Together with your students, let’s uncover the physical laws hiding behind this simple phenomenon.
In this experiment, students hang a 10 g weight from a spring and measure how much the spring stretches. For first-year junior high school students, it is an important basic exercise in science: collecting quantitative data and representing it in a graph. This is more than just following a set of instructions. It is a first step toward becoming a scientist—using numbers to make sense of how the world works.
The great thing about this experiment is that it requires almost no preparation. It works well to have all the equipment gathered in one place and let the students come and collect what they need themselves. Scientific inquiry begins the moment students take responsibility for preparing their own equipment.
You will need about five 10 g weights, a spring, a stand, a ruler, and a pair of wooden chopsticks or something similar. It can also be interesting to let the students decide some of the experimental procedures themselves, such as how often to take measurements and how far to stretch the spring. There is hardly any danger involved, either. I usually prepare one set for each group, but personally, I recommend working in pairs with one set of equipment. Having two students work together tends to lead to much deeper discussion.
A few simple tricks can make the experiment run even more smoothly. If you attach two clamps to the stand, one can be used to hold the ruler while the other supports the spring. Attach a pair of chopsticks to the clip, and you can hang the spring from them.
The complete setup
A closer look…
One useful trick for taking measurements is to measure the spring’s total length first, then subtract the original length afterward to calculate how much it has stretched. That extra step of doing the subtraction can become a valuable opportunity for students to think about what their data actually means.
When taking measurements, it is important to follow the rule also found in the textbook: read the scale to one-tenth of the smallest marked division. This is one of the basic rules for collecting accurate data. For example, being able to distinguish between a spring stretch of 4.3 cm and 4.4 cm makes the data much more reliable. Paying attention to such tiny differences may even be what leads to a major discovery someday.
Example worksheet:
Experimental Results and Hooke’s Law
When students plot their experimental results, there is a wonderful moment when all those seemingly random numbers suddenly line up to form a beautiful straight line. This is one of the real joys of science! But there is something even more interesting: if you ask students to predict what the graph of the spring’s stretch will look like before starting the experiment, many of them struggle to give an immediate answer.
They may have a vague feeling that it will probably be a straight line, but when you ask, “Why should it be a straight line?”, they often find it surprisingly difficult to explain. For all we know, the graph might curve and the spring might suddenly stop stretching beyond a certain point. That little sense of “Wait, why?” is exactly the kind of spark that fuels scientific curiosity.
Why Does the Graph Become a Straight Line? The Beauty of Proportionality Discovered by a 17th-Century Genius
According to Hooke’s law, the amount a spring stretches is proportional to the weight of the object hanging from it, or more precisely, the force applied to it. In other words, if you double the weight, the spring stretches twice as much. This is what we call a proportional relationship.
The scientist who discovered this relationship was Robert Hooke, a 17th-century English physicist. He is also famous as a rival of Isaac Newton and as the person who first observed cells using a microscope. By investigating the relationship between the force exerted by a spring and its extension, he proposed what we now know as Hooke’s law: the extension of a spring is proportional to the force applied to it.
Thanks to this simple law, we can answer questions such as “How far will the spring stretch if we hang ten weights from it?” without actually having to perform the experiment. We can calculate it—and make a prediction—beforehand.
I’ve put together some ideas for making an investigation of Hooke’s law even more inquiry-based in the following article. Be sure to check it out as well.
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