Archimedes’ Principle:
This is a principle that was named after the owner Archimedes. He discovered that when he stepped into a bath tub filled with water, the level of the water rose by a certain amount.
Use the interactive simulation at http://phet.colorado.edu/sims/density-and-buoyancy/buoyancy_en.html to help rediscover what Archimedes found for himself.
Take some time to look for the following on the simulation:
Change the object from wood, styrofoam, ice etc on the top left corner
The check boxes on the lower left corner: one set displays forces the other set displays values
The option to display one or two bricks on the top right corner.
Perform the tasks below by interacting with the simulation
Task 1: Click the ‘Buoyancy Playground’ tab.
Record the volume of liquid in the tank in liters.
Drag the block of wood into the liquid
Note the change in liquid volume.
Archimedes did some test and he found out that:
i) objects weighed less in water
Task 2: Use a brick of mass 10.0 kg. Place it on the scale on the side and record it’s weight. Place the brick on the scale in the water and record its weight. Did you notice that the weight in water is less than the weight in air?
ii) objects in a *fluid experience an upward force (upthrust)
Task 3: Display the buoyancy force by clicking the check box 'Buoyancy' (Look on the lower left hand corner)
iii) the weight of the water displaced or pushed aside is equal to the upthrust on the body
Task 4: Perform a calculation
Record the initial volume of the water
Record the weight of the brick in air (using the scale on the side)
Place the brick in the liquid on the scale
Record the change of volume of the water
Record the change in weight of the brick
Display the value of the buoyancy force by clicking the 'Force Values' check box (Look on the lower left hand corner)
Compare the weight of the water displaced to the buoyancy force, are they equal?
Archimedes principle states that when a body is wholly or partially immersed in a fluid it experiences an upthrust ( or : buoyant force) equal to the weight of the *fluid displaced.
*(Fluid meaning either gases or liquids)
Floating and sinking
Some objects float in water while others sink.
Task 5: Use two blocks one of wood and the other of brick. Place them in the water. What do you notice?
The principle of floatation states that a floating body displaces it own weight of the fluid in which it floats.
Task 6: Display only one block of styrofoam and click the buoyancy force check box.
This is how you can determine if an object will float or sink.
If the upthrust equals the weight of the object, it floats and if the upthrust is less than the weight of the object, the object will sink.
If the density of the object is less than the density of the fluid, the object will float
If the density of the object is greater than the density of the fluid, the object will sink.