Key concepts
Temperature
Physics
Engineering
Materials science

Introduction
Have you ever broken a piece of candy in half to share with a friend? Did you know you were doing a little physics activity when you were snapping that treat? You can learn even more about materials and their properties by playing around with candy in this activity. This is a fun (and tasty) way to study materials science, which includes learning how different materials break—and under what conditions. In this project you'll divide various candy bars in half then see what happens when you put them in the freezer. Do you think they'll be easier or harder to break?

Background
Materials scientists and engineers study different materials, how they bend and break, and how to make them stronger. This allows the scientists to help develop stronger, safer structures and objects. Materials can behave differently, depending on whether you stretch, bend or compress them. If you just stretch or bend a material a tiny bit, it might spring back to its original shape. For example, think about what happens when you bend a metal or plastic ruler slightly. This type of "springy" behavior is called elastic deformation. Almost all materials will show some elastic behavior (even if it's just a tiny bit) before they break.

But what happens if you bend or stretch a material too much? Some materials will continue to deform but permanently hold their bent shape instead of springing back. For example, think about what happens when you bend a paper clip. This is called plastic deformation. Materials that can undergo lots of plastic deformation before they finally break are called ductile. Other materials will break very suddenly when you bend them too much—for example, a wooden ruler or pencil. Materials that snap suddenly without undergoing much plastic deformation are called brittle.

But the behaviors of materials are not always the same; conditions such as temperature can have a great effect on how they respond. Engineers who build outdoor structures (such as bridges) or things used outside (such as cars) have to worry about how temperature changes will affect a material's behavior. You wouldn't want a structure that's nice and sturdy on a warm day to suddenly collapse if it gets hot or freezing cold! In this project you'll investigate how temperature affects what happens to different candy bars when you try to bend them in half.

Materials

• Two each of assorted full-size candy bars of your choice
• Two each of assorted "soft" candies such as Twizzlers, AirHeads or Gummi Worms (AirHeads are highly recommended because they are the best at showing the experiment's effect.)
• Pen or pencil and paper (optional)

Preparation

• Place one of each type of your candy items in the freezer about one hour before you start your experiment.
• Leave the other half of your items out at room temperature. Do you think temperature will have a large impact on these candy materials' physical behaviors?

Procedure

• Take one of your room-temperature candy items and hold it on both ends (using both hands).
• Slowly start to bend the full-size candy in half. Pay close attention to how hard it is to bend it. Is it very stiff and difficult to bend at all? Is it superflexible and easy to bend?
• Continue bending the candy until it breaks. Pay close attention to how it breaks. Does it snap very suddenly (brittle) or does it stretch out and break gradually (ductile)?
• Note: Some items, such as Twizzlers and Gummi worms, are very flexible, so you might not be able to break them at all by bending them. Can you break them by pulling them apart? If so, how does that break occur—suddenly (brittle) or stretchy and gradually (ductile)?
• If you would like to make a note of each type of candy and its material behavior during bending and breaking, record each observation after you preform the breaking test.
• Now, take the matching candy out of the freezer and repeat the steps above. Remember to carefully observe how the candy breaks. Is the candy easier or harder to bend? Does the candy break in a different manner?
• Repeat the procedure for each type of your other candy items. Remember to pay close attention to how hard the materials are to bend and how they break.
• Did the matching candies behave differently depending on their temperatures? How did different candies of the same temperature compare with one another during the bending test? What do you think would happen if you tried bending these candies when they were warmer than room temperature?

Observations and results
In this activity you should have seen that most materials became stiffer and less flexible after spending one hour in the freezer. For example, items such as Gummi Worms and Twizzlers might have been very floppy and bend under their own weight at room temperature but required a little bit of force to bend after being in the freezer. Even if they became stiffer and harder to bend with the cold, they nonetheless might not have experienced brittle breakage. This does not mean your activity went wrong—some materials are still ductile even when they are very cold! Other materials, however, may have shown a very clear transition from ductile to brittle when you froze them. This works very well with AirHeads candies and certain chocolate bars, which are gooey and stretch at room temperature (ductile) but make a very clean "snap" when frozen (brittle).

Cleanup
Remember, eating lots of candy in general is not very healthy. And eating a bunch of candy all at once can make you feel sick. Make sure you share the candy with other people—as well as save some of it for later!

More to explore
Brittle versus Ductile Deformation, from FormationStation
Stretch It! How Does Temperature Affect a Rubber Band?, from Scientific American
Science Activities for All Ages!, from Science Buddies

This activity brought to you in partnership with Science Buddies