Lesson 5: Density

Clothes Hanger Balance

Activity Developed by the University of Colorado Museum of Natural History

Description/Learning goals:

Participants will sort and classify objects based on size and weight.

Participants will practice using scientific tools to measure and make predictions.


  • Clothes hanger
  • Yarn or string
  • Paper or plastic cups
  • Hole punch

Activity Instructions:

  1. Punch a hole on either side of each cup.
  2. String with yarn and tie to either side of the hanger. You can use tape to strengthen the connection of the string and cups.
  3. Experiment with items of the same size, but are made of different materials- like plastic vs. metal spoons. Which do you think is heavier? Can you figure out how many of the lighter items equals the weight of the heavier item?

Science Concepts:

Density: Density is found by how much mass (amount of matter) is in a set amount of volume or space. If there is a lot of mass in a small amount of space, the object is very dense. So, if you have two objects of the same volume- like two round balls, but one is more dense than the other, that ball will be heavier.

Floating Objects: To have an object float in water, it must be less dense than the water it is sitting in. Remember density isn’t necessarily tied to weight- a large log can float in water while a tiny piece of sand will sink- because the log is less dense than the water.

Early Learning 101:

Classify, compare, and contrast objects, events, and experiences

Have your child compare objects throughout your house based off of size. Can you find multiple objects of a certain shape and size? Like round, and fits in the palm of your hand. Which do they think will be heavier?

Follow Up:

Talk with your child about the objects around the house they found that were the heaviest. Do they think that any of these object will float in water? Experiment with objects around the house to see if you can find objects of less density than water.

One fun way to test this is to get an orange or clementine and see if it floats while unpeeled. Then peel the orange and try again. Because of the porous skin of the orange, air is allowed to be trapped, helping the unpeeled orange to float.

Book Suggestion: Things that Float and Things that Don’t by David Adler