Valentine’s Day is almost here, and it’s not all about chocolate and cards and other tokens of affection. It’s a great time for your kids to fall in love with STEM. 

This Valentine’s Day, take the opportunity ­– and some leftover candy hearts! ­– to connect with your kids while introducing them to or helping them learn more about two basic, interconnected concepts of physics: mass and gravity. Try these three activities, and by the end, we think your kids will heart physics too.

Note: These activities are designed for kids 5-10 years old. Younger kids can participate but may not understand the concepts that underpin these projects/experiments. Feel free to alter the questions or activity based on the ages or skill levels of the children who are participating.

1. Candy Hearts: Sink or Float?

Drop different types of candy in water to demonstrate mass and weight.

The Science: An object’s mass is based on the object’s matter, which does not change. But an object’s weight may be different depending on where it is located1. For example, the weight of an object on Earth will differ compared to its weight on other planets, because the force of gravity differs from one planet to another. For the purposes of this experiment, we’ll focus on the object’s weight on Earth.

What You’ll Need:

  • Four different types of heart-shaped candies or candies in different sizes and weights
    • Suggestions: Heart-shaped fruit snacks, tiny conversation hearts, large conversation hearts, and marshmallow hearts
  • Large bowl filled with water
  • Kitchen scale (optional)

Objective: Predict whether each heart-shaped candy will sink or float when dropped into the bowl of water.


  • Invite your kids to draw or write their predictions on paper. Which will sink? Which will float?
  • Ask: How are the four different candies alike? How are they different? Ask them to hold each one and describe its physical characteristics. What is its size? Is it heavier or lighter than the others? Ask older kids if they know what mass is. Let kids weigh the objects with a scale, if available, to determine their weight when making their hypotheses.
  • As they make their predictions, ask them what went into each hypothesis.
  • Drop each candy into the bowl of water.
  • Did it sink or float? Record the result.

Reflection Questions:

  • Why did each candy float or sink?
  • Does the size and/or weight of an object affect the result? If so, how?

2. Candy Heart Tower

Build a tower to demonstrate gravity.

The Science: Gravity is an invisible force that keeps objects pulling toward each other. It keeps objects on Earth from floating into the air, and it pulls objects toward the ground when they are dropped. It is also what pulls unbalanced objects down to Earth. (Want more kid-friendly info? Check out NASA’s gravity explainer.

What You’ll Need:

  • At least two different types of candy hearts (try large and small conversation hearts)
  • Stable surface for stacking

Objective: Predict how many candy hearts you think you can stack in a single tower before they fall over.


  • Ask kids to look at the candy “building blocks” for their towers and predict how many they can stack without the stack falling over. Each child will create their towers using only one type of candy.
  • Have them write down the number for their prediction.
  • Ask them to stack the hearts straight up, counting as they go. Stop counting when the tower falls. Have kids record the result.

Reflection Questions:

  • What was easy? What was challenging?
  • What worked well? What didn’t?
  • What surprised you?
  • What would you do differently next time?

3. Candy Hearts Structure Challenge

This experiment helps demonstrate both mass and gravity.

The Science: An object’s center of gravity, or center of mass, is determined by the way the object’s weight is distributed. A balanced structure is one that has equally distributed weight so that one side does not tip over. This activity enables kids to learn more about a complex concept through a deceptively simple engineering task.

What You’ll Need:

  • Toothpicks
  • Heart-shaped gummy or heart-shaped fruit snacks (feel free to sub other shapes)
  • Timer
  • Stable surface to build on

Objective: Build the tallest freestanding structure within 10 minutes using gummy and toothpicks.


  • To help introduce younger kids to this concept, here’s a quick experiment to get them started:
    1. Place one gummy candy on the end of a toothpick.
    2. Ask your child to try balancing it horizontally on their finger.
    3. When that is unsuccessful, ask them to skewer another gummy on the opposite end.
    4. Have them try to balance the toothpick on their finger horizontally. Ask them where they need to hold the toothpick in order to balance it.
    5. Add a second gummy candy to the end of the toothpick. Ask them to try to balance it again. What happens when they try balancing it from the center? Remind them to think about this as they build their structure.
  • Invite your child to build a structure using toothpicks connected on the ends by gummy candies. When 10 minutes are up, ask them to reflect on the experience.

Reflection Questions:

  • What worked well?
  • What was challenging?
  • What would you do differently next time?
  • Why do you think your structure toppled or stayed upright?
  • Was the structure balanced?

More Exciting STEM Activities at STEMful!

If you and your child loved these activities, we invite you to enroll them in one of our STEMful programs at our education studio in San Francisco. As partners in your child’s education, we offer hands-on projects to sprout kids’ curiosity and foster a lifelong love of learning. Check out our summer camps, school break camps, afterschool programs, and more!

  1. Carl R. Nave, “Mass and Weight,” HyperPhysics, Georgia State University, 2017,