# How to Use a Spring Scale

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• 0:00 What Is a Spring Scale?
• 1:24 Mass Versus Weight
• 2:21 How Spring Scales Work
• 3:28 How to Use a Spring Scale
• 4:10 Lesson Summary

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Lesson Transcript
Instructor: Joanne Abramson

Joanne has taught middle school and high school science for more than ten years and has a master's degree in education.

Did you know that a spring scale can help you find an object's weight in Newtons? What does that even mean? Keep reading to learn the answers to these questions and more!

## What Is a Spring Scale?

Say you're walking through the grocery store looking for something to make for tonight's dinner. You notice that organic broccoli is on sale for \$1.50 per pound. Since you love steamed broccoli, you grab a bundle. Not wanting to be surprised by the price when you check out, you search for a produce scale. You find one hanging from the ceiling not too far away, and drop your broccoli in the basket. The scale bounces around for a moment and the dial above the basket finally settles on a weight of just under one pound. Congratulations! Not only have you found a tasty and nutritious side dish, you have also just used a spring scale!

A spring scale, sometimes called a spring balance, is a device used to measure the weight of an object. It hangs from above and consists of a spring with a hook at the bottom where you can attach an object. Notice that we said a spring scale measures the weight of an object, not its mass. In everyday speech, we use mass and weight interchangeably (and we'll discuss why a little bit later). In science however, these terms have very different meanings. It is important to recognize these differences in order to properly understand how a spring scale works. Now, let's look at the difference between mass and weight.

## Mass Versus Weight

In the simplest sense, the mass of an object is a measure of how much matter, or 'stuff' is in an object. For example, a golf ball and a ping pong ball may be about the same size. The golf ball, however, has a higher mass than the ping pong ball; it has much more 'stuff' inside of it. An object's mass never changes.

Weight, however, is the force exerted on an object due to gravity. Thus, an object's weight will change based on how much gravity it is experiencing. For example, since the gravity of the moon is about one sixth that of Earth, a 120-pound person on Earth would weigh about 20 pounds on the moon. That person's mass, however, stays the same. This is why, by the way, you hear about objects in space being weightless; there is no gravity to act on them.

## How Spring Scales Work

A spring scale works on a principle discovered in the 17th century by Robert Hooke. Hooke's Law states that the force required to extend a spring is directly proportional to how far out the spring is pulled. So, if we hold a spring by one of its ends, and we hang an object, such as your broccoli, off of the other, we can then measure how far the spring has been extended. Using Hooke's Law, we can take this distance and figure out the force due to gravity being exerted. This force is the broccoli's weight.

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