http://www.ck12.org Chapter 4. Motion and Forces
weight of the fluid displaced by the object. This is known asArchimedes’ law(or Archimedes’ principle). For an
entertaining video presentation of Archimedes’ law, go to this URL:
http://videos.howstuffworks.com/discovery/6540-mythbusters-lets-talk-buoyancy-video.htm
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/82418Floating Objects and Archimedes’ Law
Archimedes’ law explains why some objects float in fluids even though they are very heavy. It all depends on how
much fluid they displace. The cruise ship pictured in the opening image is extremely heavy, yet it stays afloat. If a
steel ball with the same weight as the ship were placed in water, it would sink to the bottom. This is modeled in the
Figure4.69. The reason the ball sinks is that its shape is very compact, so it displaces relatively little water. The
volume of water displaced by the steel ball weighs less than the ball itself, so the buoyant force is not as great as the
force of gravity pulling down on the ball. Thus, the ball sinks.
FIGURE 4.69
Now look at the ship’s hull in theFigure4.69. Its shape causes the ship to displace much more water than the ball.
In fact, the weight of the displaced water is greater than the weight of the ship. As a result, the buoyant force is
greater than the force of gravity acting on the ship, so the ship floats.
Q: Why might you be more likely to float in water if you stretch out your body rather than curl up into a ball?