# Density and unit weight relationship

### Difference Between Density and Weight | Difference Between | Density vs Weight

Soil weight is most often expressed on a soil volume basis rather than on a particle basis. Bulk density is defined as the dry weight of soil per unit volume of soil. It may be however that you mean the specific weight, which is the weight per volume that an object has in relation to its position. This is equal to its density. Unit weight: γ = ρg. Unit weight is the product of density and gravity acceleration. It is the gravitational force caused by the mass of material within a unit volume.

The Formula for Specific Gravity The formula for specific gravity, given that the reference substance is water, is the density of the object divided by the density of the water.

### Specific weight - Wikipedia

Here, we use the Greek symbol Rho to indicate density. The specific gravity has no unit because the units of the numerator and the denominator are the same, so they just cancel each other out. Let's look at an example. The density is directly related to the mass of the object unit: The mass itself is directly related to the weight of an object, measured in units called Newtons. So, the specific gravity can also be solved by dividing the weights of the object and the water.

Note that in all of these the units are the same so the result will have no units as they'll cancel each other out. When we throw pennies in water fountains to make a wish, the pennies sink to the bottom. That's because the pennies are denser than water. If we plug the pennies into the specific gravity formula as our object, we'd find that the specific gravity would be greater than one.

When the specific gravity is greater than one, the object will sink, and when the specific gravity is less than one, then the object will float. If the specific gravity is equal to one', this means that the object will neither sink nor float -- it will hover in the liquid. The results of chemical weathering are generally fine soils with separate mineral grains, such as Clays and Clay-Silts.

The type of clay mineral depends on the parent rock and on local drainage. Some minerals, such as quartz, are resistant to the chemical weathering and remain unchanged.

It is the principal constituent of sands and silts, and the most abundant soil mineral. It occurs as equidimensional hard grains. It is responsible for the widespread red or pink colouration in rocks and soils. It can form a cement in rocks, or a duricrust in soils in arid climates. Some are resistant, e.

They are very flaky and therefore have very large surface areas. They are major constituents of clay soils, although clay soil also contains silt sized particles. Origins, formation and mineralogy Clay minerals Clay minerals are produced mainly from the chemical weathering and decomposition of feldspars, such as orthoclase and plagioclase, and some micas.

It is important that the lower length of the straw be made just long enough to extend from the top of the paper clip "bail" to the bottom of the card with the rubber band sticking out the top. You must be able to tie the rubber band to the string and have the junction of the two be on the lower end of the 3 X 5 with nothing in the cup.

This is the "below" referred to in the above paragraph. We decided it would take a large image to show the necessary details so, if you have the time, click here for Weight Scale Construction Details.

After the students have calibrated the Weight Scale, it might be fun to have them see if they can guess how many pennies have been loaded into their cup by another student.

From this they will learn how to read between the marks they have placed on their cards this is called interpolation and they will also learn that the scale is really not too accurate. However, all instruments are less than perfect at some level and this crude scale should help them to realize this fact. We think it is nice that the scale is quite inexpensive and students who wish can construct one at home.

This Weight Scale can also be used to measure some of the other materials that were measured with the Mass Balance. Hopefully they will find that they will get pretty close to the same answer in "pennies" for the mass as measured on the Mass Balance and the weight as measured on the Weight Scale.

So you ask--what is the difference between weight and mass?

## What is Density, Specific Weight, Specific Volume and Specific Gravity?

Now comes the key question to ask the class: If you took the Mass Balance and your calibrated Weight Scale to the Moon, do you think they would give the same measurement as on Earth?

Remember, you always balance the unknown object against several pennies with the Mass Balance but you just let the unknown object pull down against the calibrated rubber band on the Weight Scale. We hope that this thought experiment will help the students see that the Mass Balance will measure the same no matter where you locate it in space but the Weight Scale, which measures how hard gravity pulls down on the object, will give a smaller reading on the moon.

This is confusing stuff and most college students will have difficulty understanding it. Perhaps if your kids start thinking about it early enough, they may come to a better understanding of the difference between weight and mass when they are older. Since density is mass per volume, the most straight forward way of measuring the density of something is to measure its mass, then measure its volume and divide the mass by the volume.

We could do exactly that in this activity but at this point we have no good way to measure volume. If you have a graduated cylinder they aren't expensive but most elementary schools don't have them you could use it with some water to mark the small "portion cups" at specific volumes. We have already suggested that the small 1 oz cups will hold 10 cubic centimeters when filled to a point 1. Rather than actually measuring the density, we feel it will be sufficient for the students to appreciate that the same volume can be a large mass or a small mass depending upon the material involved.

Our plan is to have the same volume of several different materials and measure their mass with the Mass Balance. Hopefully this exercise will help the students to begin to see the relationship between mass, volume and density.

### Background on Mass, Weight and Density

The next page begins the "Student Activity Sheet". We suggest that these be reproduced in sufficient numbers for the entire class. Whether the students work individually or in groups is best decided by you, however, some of the exercises need at least two people to hold and use the apparatus.

Mass, Weight and Density--how matter is measured, how it interacts with other matter and how it fills space. Which is heavier, a pound of feathers or a pound of lead?

If you have never heard this old trick question before--think about it. Now try this one: Finally, think about this one: The answer to each of these questions requires that you understand the difference between mass, weight and density.

You will measure the mass of objects by comparing them to the mass of pennies with a thing we will call a "Mass Balance".

• References :
• Density vs. Weight
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Although mass is usually measured in kilograms or grams, we will measure mass in "pennies". The Mass Balance is shown below. This balance measures mass in "penny" units. First test the Mass Balance to see if it is "zeroed". When you lift it by the center paper clip, it should stay fairly level. When the clip is in the top hole, it will balance easily.

If you put the clip in the bottom hole, it probably will be too sensitive to balance at all. Test the Mass Balance by placing 5 pennies in both cups and gently lift it off the table--it should balance.

Have one student secretly place a number of pennies in one cup and see if you can figure out how many pennies there are in the cup by matching them with pennies in the other cup. You will find that not all pennies are exactly the same. After you learn how to use the Mass Balance, you will be given several different materials to measure.

Always measure the same volume of the given materials, that is, always fill the material to the same level on the cup on the left and find its mass by placing pennies in the cup on the right. Record your data in a table like the one below: Name of material being measured Mass of material in "pennies" name first materal meaured here record its mass in pennies here etc.

## Specific weight

Here is an important question to think about: If you took your Mass Balance to the Moon and repeated this experiment, would you get the same result? Have your teacher discuss with you what mass means--this is quite confusing to many people. You will construct and calibrate a Weight Scale. This scale works by measuring how far a certain number of pennies are able to stretch a piece of rubber band. The scale is illustrated below: Measuring weight in units of pennies.

After you have constructed the Weight Scale your teacher will give you instructions you will calibrate it using pennies. While one student carefully holds the Weight Scale by the string the other student will make a line on the card. First mark on the card where the knot touches the card with nothing in the cup this will be the zero line on the scale.

Now add 5 pennies to the cup and carefully mark where the knot touches the card. Practice with pencil first until you learn how to do this.

Carefully "calibrate" your scale by adding 5 pennies at a time and marking where the knot touches the card. The numbers on your scale will be 0, 5, 10, 15, 20, 25 you probably will not be able to get any more. Don't expect the numbers to be evenly spaced--rubber bands don't work that way.