How Strong is Your Chocolate Lesson

How Strong is your Chocolate at a glance

Background

Ever wondered how engineers ensure that a bridge, building, or even a chocolate bar can handle everyday pressures? In this lesson, students will explore the world of material testing to find out! Materials like metals, ceramics, and plastics are tested to determine how much force they can withstand before breaking, a process known as strength testing. Engineers use these tests to ensure materials are strong enough for their intended purposes, whether it's supporting cars on a bridge or keeping a milk jug intact.

Students will learn about various tests that measure material strength, focusing on stress testing. Stress is the force applied to a material divided by the area over which the force is applied. By testing materials like aluminum, iron, or plastic, students will see how much stress each material can endure before failing.

To make the lesson relatable, students will examine chocolate bars. Despite having the same basic ingredients, chocolate bars can vary in strength based on their contents, like almonds or crispy rice. This variation mirrors how different materials, even with similar properties, can perform differently based on their microstructure. By testing chocolate bars, students will understand how material structure affects strength and why this knowledge is crucial for designing safe, effective materials.

Lesson Objective

Explore how different microstructures affect the strength of materials by testing chocolate bars with varying additives. Students will learn about the impact of material composition on flexural strength through a hands-on bending test.

Experiment Description

Students will use a 3-point bending test to measure the flexural strength of chocolate bars with different microstructures (plain, almond, and crisped rice). They will calculate the stress the chocolate bars can withstand before breaking, analyzing how variations in microstructure influence material strength.

Materials List

5 plastic cups with twine
1 mass balance
350 pennies (or alternative mass objects)
5 protective mats
5 rulers
5 milk chocolate bars (plain, almond, and crisped rice, one of each type per group)

Safety Precautions

Standard lab procedures should be followed to ensure safety, including using materials as directed and avoiding any food contamination or misuse.

The Experiment

1. Set up two desks or tables so that a chocolate bar can be placed across them with some of the bar hanging off the edge on each side.

2. Put a protective mat on the floor underneath to catch any chocolate that might fall.

3. Next, measure and write down the width and thickness of each chocolate bar you are testing.

4. Place the chocolate bar on the desks so it is supported at each end, and hang a cup with some twine in the middle of the bar. Use a funnel to slowly add pennies to the cup until the chocolate bar breaks.

5. As you add pennies, watch for any bending or changes in the bar. When the bar breaks, count how many pennies were in the cup.

6. Weigh the cup, twine, and pennies to find out how much force was applied to the bar.

7. Use this information to figure out the strength of the chocolate bar by using a special formula. Repeat the experiment with different kinds of chocolate bars to see which one is the strongest.

8. After you’re done, clean up the chocolate mess, and make sure to eat any leftover chocolate!