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For more information, please see full course syllabus of Physical Science
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Lecture Comments (6)

0 answers

Post by Yisrael Harris on May 5, 2013

I have completed the entire Physical Science course, and I would like to say that I enjoyed it very much.

1 answer

Last reply by: Professor Ebs
Thu May 2, 2013 10:03 PM

Post by Yisrael Harris on May 2, 2013

What if an object's density equals exactly that of water?

0 answers

Post by Saakshi Dhingra on April 14, 2013

Does the temperature of the water affect the weight of the amount of displaced water?

0 answers

Post by shaminder makh on April 6, 2013

very helpful

0 answers

Post by Nathanael Shim on December 7, 2012

wow this lesson is so cool...

Density & Buoyancy

  • Density is the amount of matter in a given amount of space.
  • Density = mass/volume (g/mL) or (g/cm3)
  • Buoyancy is an upward force that keeps things afloat.
  • Archimedes’ principle - A body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid.
  • If the weight of water that is displaced by an object in water exceeds the weight of the object then the object will float.
  • If an object is less dense than the fluid in which it is placed, it will float.
  • If it is more dense than the fluid, it will sink.
  • When the volume of an object is LARGER than the mass, the density is less than 1.0 g/cm3

Density & Buoyancy

What is the density of an object that has a mass of 10g and a volume of 10mL?
Density = 1g/mL
If two objects had the same volume, how could you determine which object is more dense?
The object that has more mass is more dense when the volume is the same.
How do you measure the volume of an irregularly shaped object?
Use the water displacement method
What is the volume of an object that causes the water level to rise from 20mL to 25mL when the object is placed in water?
What is the upward force that keeps things afloat?
Buoyant force
What force depends on your mass and the gravitational acceleration of the Earth?
According to Archimedes principle, the weight of the water displaced by an object equals what force?
The buoyant force on the object
If the buoyant force is less than the weight of the object, will the object float?
No, the buoyant force must be greater than the weight for the object to float.
What will happen to an object that is more dense than water when you put it into water?
The object will sink
If the mass of the water displaced by an object is 1kg and the gravitational acceleration of the Earth is 9.8 m/s2, will the object that has a weight of 10N float?
No — The weight of the water displaced is 9.8N (mass x gravitational acceleration)

*These practice questions are only helpful when you work on them offline on a piece of paper and then use the solution steps function to check your answer.


Density & Buoyancy

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Density 0:05
    • Definition of Density
    • Density = Mass / Volume
  • Density of Irregular Objects 3:58
    • Density of Irregular Objects
  • Buoyant Force 7:46
    • Buoyancy
    • Archimedes' Principle
  • Floating and Sinking 12:47
    • Floating and Sinking: Looking at Density
  • Example 1: Density of an Object 16:15
  • Example 2: Density of Yourself 17:28
  • Example 3: Using Archimedes' Principle to Predict If an Object Will Sink or Float in Water 19:38
  • Example 4: Will Aluminum, Gold, and Oil Float or Sink When Placed Into Water? 22:06