Mass versus weight - Wikipedia
We hope we can explain the difference between mass, weight and density so Usually we spend most of our time on Earth so our weight is the force that the . the students to begin to see the relationship between mass, volume and density. "They divide the mass of the Earth by the volume, which gives the average of the Earth you need more information than just the volume of a sphere formula. All solar planets are found on the horizontal level relative to the Earth. 3. The Sun is What is the relation between density, mass, and volume in science?.
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.
Relationship between Gravity and Density | Physics Forums
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? 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.
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".
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.
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.
If you have calibrated your scale well, you should be able to tell how many pennies someone has placed in the cup without actually counting them.
As with the mass balance, you should weigh some of the materials your teacher provides.
Earth mass - Wikipedia
Always fill the cup with the same volume of material. Make a table like the following: In the case of liquids and solids, the reference material is fresh water. Specific gravity is calculated by dividing the density of a substance by the reference substance's density.
For example, gold has a density of This yields a specific gravity of This means gold is Buoyancy Whether an object floats or sinks is determined by the downward force of gravity and an upward buoyant force. If the buoyant force is greater, an object floats.
If the force of gravity is greater an object sinks. The interplay between these forces is related to the density of the object and the density of the fluid it is placed in. If the overall density of the object is greater than the liquid, the object sinks.
If the overall density of the object is less than the liquid then the object floats. A common helium-filled toy balloon is something familiar to many. When such a balloon is fully filled with helium, it has buoyancy —a force that opposes gravity. When a toy balloon becomes partially deflated, it will often become neutrally buoyant and can float about the house a meter or two off the floor.
In such a state, there are moments when the balloon is neither rising nor falling and—in the sense that a scale placed under it will have no force applied to it—is, in a sense perfectly weightless actually as noted below, weight has merely been redistributed along the Earth's surface so it cannot be measured.
Though the rubber comprising the balloon has a mass of only a few grams, which might be almost unnoticeable, the rubber still retains all its mass when inflated. If one were however to weigh a small wading pool that someone then entered and began floating in, they would find that the full weight of the person was being borne by the pool and, ultimately, the scale underneath the pool.
However, as noted, an object supported by a fluid is fundamentally no different from an object supported by a sling or cable—the weight has merely been transferred to another location, not made to disappear.
The mass of "weightless" neutrally buoyant balloons can be better appreciated with much larger hot air balloons. Buoyancy and the resultant reduction in the downward force of objects being weighed underlies Archimedes' principlewhich states that the buoyancy force is equal to the weight of the fluid that the object displaces. If this fluid is air, the force may be small.
Buoyancy effects of air on measurement[ edit ] Normally, the effect of air buoyancy on objects of normal density is too small to be of any consequence in day-to-day activities.
For convenience, a standard value of buoyancy relative to stainless steel was developed for metrology work and this results in the term "conventional mass".
Since objects with precisely the same mass but with different densities displace different volumes and therefore have different buoyancies and weights, any object measured on this scale compared to a stainless steel mass standard has its conventional mass measured; that is, its true mass minus an unknown degree of buoyancy.
In high-accuracy work, the volume of the article can be measured to mathematically null the effect of buoyancy. Types of scales and what they measure[ edit ] A balance-type weighing scale: Unaffected by the strength of gravity.
Load-cell based bathroom scale: Affected by the strength of gravity. This is because balances "dual-pan" mass comparators compare the gravitational force exerted on the person on the platform with that on the sliding counterweights on the beams; gravity is the force-generating mechanism that allows the needle to diverge from the "balanced" null point.
Mass versus weight
These balances could be moved from Earth's equator to the poles and give exactly the same measurement, i. But if you step onto spring-based or digital load cell -based scales single-pan devicesyou are having your weight gravitational force measured; and variations in the strength of the gravitational field affect the reading.
In practice, when such scales are used in commerce or hospitals, they are often adjusted on-site and certified on that basis, so that the mass they measure, expressed in pounds or kilograms, is at the desired level of accuracy.