Try mix a few liquids together in a jug, and see what floats and what sinks to the bottom. Those at the bottom are denser. Steel ships float because even though steel is denser than water, their hulls are full of air.
They sink until enough water has been moved to match the weight of steel and air in the hull. Ships float at different heights depending on how heavily laden they are and how dense the water is. So if you see one floating higher than another, now you know why!
Ships float higher in sea water than in fresh water because salt makes the sea water denser. Wow, who would have thought? Ships float higher in dense cold seas than in warm tropical ones which mean they also float higher in the winter months. Molecules — tiny particles in objects that can only be seen under a microscope. Gravity — a force which tries to pull two objects toward each other. Buoyancy — how something can float in water or air.
Density — This is about how loosely or tightly packed molecules are in an object. Although the standard does not call for density to be used as a characteristic property to identify a substance, a basic introduction to density is included here as an optional element of a learning progression leading up to a middle school understanding of density.
Download the student activity sheet and distribute one per student when specified in the activity. The activity sheet will serve as the Evaluate component of the 5-E lesson plan.
Students will record their observations, and answer questions about the activity on the activity sheet. If students dip the tiny piece of clay in the water beforehand and then put it back on the surface of the water, it should sink.
Show the Animation — Density: Clay and Water. Explain that density has to do with how heavy something is compared to its size. As you show the animation, explain that since a piece of clay weighs more than the same amount, or volume, of water, clay is more dense than water. Since clay is more dense than water, a ball of clay sinks in water, no matter how big or small the ball of clay is. Show the Animation — Density: Wood and Water.
If you compared the weight of wood and an equal amount, or volume, of water the sample of wood would weigh less than the sample of water. This means that wood is less dense than water. Since wood is less dense than water, wood floats in water, no matter how big or small the piece of wood is.
The key to floating is being light for your size. So if you can add size to an object without adding much weight, the object will be lighter relative to its size. This means that the density of the overall object will decrease and be more likely to float. Ask students to describe how this principle can be used to explain how a lifejacket can help someone float in water.
The key to sinking is being heavy for your size. If you can add weight to an object without adding much size, the object will be heavier relative to its size. This means that the density of the overall object will increase and be more likely to sink.
Ask students to explain how this principle can be used to explain how a weight belt can help a SCUBA diver sink in water when they might otherwise float. Note: A student might want to know why a boat made out of steel can float when steel is more dense than water. This is not an easy question and requires a different approach than what students have seen so far.
We do not necessarily recommend the following explanation for 5 th graders but here is the idea:. An object floats when it displaces a volume of water that has a mass equal to the mass of the object. So if a material like steel is shaped into a boat and made larger and larger, it will displace more and more water. When it is large enough to displace a volume of water that has a mass equal to the mass of the boat, the boat will float.
Careers Launch and grow your career with career services and resources. The critical observation is to see what happens to two blocks.
One should be a low density material such as wood, but with a large mass i. The other should be a metallic object with a smaller mass than the wood. A coin would do. Holding the two objects will give pupils a clear and immediate sense of a difference in mass. Following a prediction about which will float, the two objects can be lowered into a sink or bowl full of water. For materials, it is some feature of the material, as opposed to the object itself, that determines if it will float or sink.
Mass is a characteristic of a particular object. Volume is also a characteristic of a particular object. Density is an intrinsic property of a material. For deciding about objects, again the target concept is the compound property of density, not the contributing concepts of mass or volume alone. For 6 Resources.
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