In our previous article, we laid the groundwork for understanding the mechanics of elastic springs and how they apply to popular PSLE Science questions. Today, we’re going to explore an exciting real-life application of elastic springs – the iconic Pez candy dispenser! Have you ever wondered how this sweet treat contraption actually works?
Join us on a journey to uncover the mechanics behind this beloved candy dispenser and explore the captivating concept of elastic spring force that gives it its charm. Get ready to be amazed by the hidden wonders behind this delightful object.
Elastic Spring – Candy Dispenser Question [Rosyth School P6 WA2 2023 Q19]
Qn: Mrs Tan performed an experiment on two different types of springs, X and Y, of the same length using the set-up shown in the diagram below.
She measured the length of the springs for different weights and used the readings to plot a graph as shown below.
(a) What is the relationship between the mass of the weights and length of the springs? [1m]
Reading the graph:
On the horizontal axis, as we move to the right, the mass of the weight used increases.
Now let’s look at the vertical axis. For both spring Y and X, the graph is a downwards slope, which means the length of the spring is decreasing.
Suggested answer: As the mass of the weights increase, the length of the springs decrease.
Qn: Mrs Tan placed spring X into a sweet dispenser. When she lifts the head, the sweet moves out of the dispenser to the top as shown in the diagram below.
(b) Explain in terms of forces, how spring X helps to remove the sweet from the dispenser. 
Key information: Explain in terms of forces, not energy. E.g., elastic spring force, frictional force etc.
In this case, it should be elastic spring force due to the spring.
What is elastic spring force?
Have you ever stretched or compressed a spring and felt its resistance? Springs possess a unique property of material known as elasticity. When an elastic object, such as a spring, is stretched or compressed, a force is exerted on the stretching or compressing object . This is called elastic spring force, which also makes the object return to its original length.
Mechanism of the dispenser:
From the question, we can tell that using the candy dispenser involves two steps.
Step 1: Placing the candy in the dispenser
Step 2: Removing the head to dispense the candy
If you’ve ever come across a Pez candy dispenser, you’ll undoubtedly recall its playful design, often featuring a cute character or a whimsical head on top. However, the real magic lies in the simple yet fascinating mechanism hidden within. As you slide the head backward, like pulling a tiny lever, something enchanting occurs – a delightful piece of candy pops out from the dispenser. Here’s what is happening.
Suggested answer: The compressed spring X exerts an elastic spring force on the sweets, when it returns to its original length and pushes the sweets upwards.
(c) Next, Mrs Tan changes spring X to spring Y. She observed that the sweet in the dispenser moved a shorter distance. Explain why.
Looking at the graph, spring Y compressed a total distance of 2 units, less than spring X which compressed a total distance of 5 units.
Elasticity and Compressed Distance:
For elastic materials, the more elastic an object is, the longer the distance moved when compressed. A more elastic spring will therefore become shorter when compressed with the same force/weight.
Since spring Y moves a shorter distance than spring X with the same weight, Spring Y is less elastic or stiffer.
Suggested answer: Spring Y is stiffer than X. Therefore, it will be compressed less for the same weight of the sweets. Hence, there is less elastic spring force exerted on the spring and pushes out the sweet with less force.
So, the next time you use a Pez candy dispenser, remember that it’s not just another toy—it’s a clever application of elastic spring force.
Read Also: PSLE Science: Elastic Spring Force Graph