a PLAYCHEM experiment

Matter is defined as something having mass and occuping space.

The ratio of mass to space occupied is called DENSITY.

Mathematically, DENSITY is defined as.............. Density = Mass/Volume

One method of determining density involves measuring both weight and volume. Weight is measured using a balance. There are several ways of measuring the Volume of an object.

  1. Using geometry and the dimensions of a regular object
  2. Measuring the weight or volume of a liquid displaced by the object when totally immersed.

Method 2. can take on some sophisticated logic and that is the case for this experiment. The objects you will measure will have some irregularity so you will measure their volume using the concept of buoyancy in a liquid. As a brief introduction:

  • If an insoluble object is immersed in a fluid under the influence of gravity:
    • an object less dense than the fluid will float. It displaces its weight of fluid.
    • an object more dense will sink. It displaces its volume of fluid
    • an object of equal density will remain suspended under the fluid's surface, neither sinking nor floating. Since it is completely underwater, it displaces its volume of fluid. And since the object and fluid have the same density it also displaces its weight of fluid.

To determine the density of your UNKNOWN Object, you will make three weighings involving a container of water with or without your object. You will also need the density of water. Two of the weighings you will make are shown below.

The above pictures show weighing an object in a liquid.

  • On the left , the Energizer® battery is simply sitting in a container of water. It is sitting on the bottom.
  • On the right, the same battery is suspended by a string in the same container of water so that it is competely submerged but not touching the sides or bottom.

The balance shows a clear difference in weight! Since neither the amount of water nor the objects have changed, the difference in weigh must be due to the difference of the battery sinking to the bottom or being suspended in the water.

Before going on, ask yourself these questions:

  1. Would the weight on the left change if instead of the battery being sunk in the container of water, it was placed next to the container on the balance pan?
  2. Would the weight on the right change if the battery were suspended in air next to the container rather than suspended in the water in the container?
  3. What is the third weighing which is needed to determine density?
  4. If you spill some of the water between weighings, would it make a difference?

To understand what is happening, click on................. answers

For an interesting modification, click on..................... modification

At this point you can start this experiment by going to "hades". Once in hades, at the "Username:" prompt, type PRELAB and press Enter. Then follow directions on the screen. If you have a Telnet Application on your computer, to get to hades, simply click the TO START. Then type PRELAB etc...TO START