Floating and Sinking Eggs
Lesson Plan
Amount of time Demo takes:​ 1-2 mins.
Try this at home!
Materials
● Large clear cup of salt water (12 oz water)
● Large clear cup of tap water (12 oz water)
● Eggs (2/day)
● Salt (6 tbs/day)
● Tongs
Set-up Instructions
1. Fill two glasses with water.
2. Add six tablespoons of salt to one of the glasses of water and mix well.
3. Place an egg in each of the glasses.
4. Notice that the egg will float in the salt water, but sinks in the ordinary tap
water. That is because the saltwater is denser than the regular water.
Lesson’s Big Idea
● Density is a measure of how much matter takes up a certain amount of
space or volume. The more matter you can pack into a certain space, the
denser it is. Density and weight are two ​different​ measurements. Weight
the mass of an object times the force of gravity.
● Since density is defined by how much matter takes up a certain amount of
volume, we can take ordinary water, add salt to it, and make it denser.
While the volume increases a little bit when we add the salt, the mass
increases by a much bigger factor. This is because rather than just floating
around and taking up space, the salt dissolves into ions which are attracted
to the water molecules and bind very tightly to them, packing more matter
into the space. The mass of the ordinary water consists of the mass of the
hydrogen and oxygen that it contains. The saltwater has the additional
mass of the sodium and chlorine atoms that dissolve into the water. In
other words, the salt water that we create has more stuff in it and is much
denser than ordinary water.
● By understanding that the higher the density of a fluid, the easier it is for
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things to float in it. You can think of the salt water as having more
particles with which to hold up the floating object.
● This same principle applies to people swimming in oceans or salt water
lakes. The average person will sink in ordinary water, but can float like a
boat in saltwater. The Dead Sea is 33% salt by mass. People find it very
odd how “floaty” they are when they swim in the Dead Sea.
● You might not know this, but skinnier or more muscular people are denser
than fatter people. Some championship swimmers, for instance, will sink in
salt water while heavier people will still float.
Assessment/sample questions you can ask
1. Why does the egg float in one cup, but not in the other?
a. The density of the freshwater and saltwater are different.
2. What are two examples of other things that have different densities?
a. A cube of two different materials (ex: Aluminum and Lead, lead is
much more dense.
Clean Up
● Clean up between demos if needed. When completely finished gather all
materials listed for this demo and make sure everything is accounted for. If
something was used up, broken, or damaged, let someone know so it can
get replaced or fixed.
Tips & Tricks
● Warm water works best for dissolving salt
● If the egg doesn’t float in the saltwater, try adding more salt.
References
● http://www.reekoscience.com/Experiments/FloatEggInSaltwater.aspx
Next Generation Science Standards
● 2-PS1-1
● 3-PS2-1
● 5-PS1-1
● MS-PS2-1
● HS-PS2-6
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