Buoyancy study cards

What is density?

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The amount of space an object takes up in relation to the amount of mass in the object. Put another way, . . .  . . . density is how much mass there is in a particular space. Look at the amount of space the cirles take-up and how many molecules each circle contains.

Caption: : In the low density circle, there are a small number of molecules within the space of the circle (low density = light). In the high-density circle there are a large number of molecules within the space of the circle (high-density = heavy). Even though both circles take-up the same amount of space, they have a different mass / density.

What does density have to do with buoyancy?

We know that all objects have mass / density.  Some objects are light and some objects are heavy. Water and other liquids and fluids also have density.  For example, water has the the density of 1g per cubic cm. If the object put into the water is more dense than the water, it will sink. If the object put into the water is less dense than the water, it will float. 

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Caption: : Here the medium is water.

What is buoyant force?

Buoyant force is an upward force that acts on an object in a fluid.  If the object has a low-density, than the buoyant force will be greater, and the object will float. If the object has a high-density, than the buoyant force will be lesser, and the object will sink.  

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How can we make an egg float?

Normally, an egg sinks to the bottom of the glass. In order to make the egg float we had to change the density of the water to increase the buoyant force. We increased the density of the water by adding salt.

What is displacement?

Remember what happened when Archimedes got into his bathtub? Eureka!!! The water level went up.  That's displacement.  Whenever an object is placed in a fluid, like water,  the object takes-up the space of the water that was there, and that water moves away from the object.

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How can we make clay float?

Normally, clay will sink, because it's very dense / heavy and displaces a small amount of water.   We were able to make the clay float, because we changed the shape and made it hollow inside.  By doing this, the boat displaces more water than its weight. Also, the part of the boat under water is mostly air, which is less dense than water.

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