## What Is Unit In Physics

Any quantity that can be measured is called a physical quantity. The measurement of a physical quantity always involved the comparison of the quantity to be measured with a reference standard of the same kind. This reference standard used for the comparison is called the *unit* of the physical quantity.

The *standard unit**of measurement* is defined as a unit of measurement which has a fixed value that does not change from person to person or place to place. For example, second is a standard unit of measuring time. Whether a second is used by one person or another person, whether the second is used in one country or another country, it always represents exactly the same time duration. The duration of a second does not change from person to person or place to place. In fact, wherever we go in the world, a second has a fixed time duration, which never changes. Thus, a second means the same duration to everyone. So, second is a standard unit of measuring time. It is necessary to have standard units of measurements for the sake of uniformity in measurements.

## Difference Between Mass And Weight

For the majority of people, there is no difference between the mass and weight of an object. In other words, mass and weight are the same thing. Thats why they are often used as synonyms for each other .

But, in reality, let me correct myself according to their scientific definition, they are quite the opposite. So, have you ever wondered why there is so much confusion regarding that?

I mean, is mass the same as weight? Or, how is mass different from weight? Well, before answering these types of questions regarding these two physical quantities, let me give you a brief review!

## Calories For Weight Gain/weight Loss

Generally, one must eat more calories than you burn in order to gain weight. For people who desire to put on weight slowly, they can eat 300 to 500 calories over what they usually eat. Those who want to gain weight quickly should eat around 700 to 1000 calories every day.

If you are trying to lose weight, then you can calculate your calorie needs currently, and then remove 500 to 1000 calories each day. This will cause you to lose around half a kg to 1 kg every week. However, you must ensure that you dont eat less than 1200 calories per day if you are a woman, and 1800 calories per day if you are a man.

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## Can Mass Be Directly Measured Without Measuring Its Weight

From Wikipedia,

Inertial mass measures an object’s resistance to being accelerated bya force .

Active gravitationalmass measures the gravitational force exerted by an object.

Passivegravitational mass measures the gravitational force experienced by anobject in a known gravitational field.

Mass-Energy measures the totalamount of energy contained within a body, using E=mc²

For all mass measurements, we are actually measuring its force and dividing it by the gravitational acceleration, $g$. The current devices for measuring mass all works by measuring the force rather than the mass .

As for the Mass-Energy measurements, it is difficult to measure the total amount of energy as it comprises many factors

Even for measuring the mass of celestial objects , the Newton law of gravitation is used, which also measures the force and applying the equation to obtain its mass.

Are there any methods or devices that directly measure the mass, without measuring the force and manipulating it to get the mass?

- $\begingroup$One way might be measuring the amount space-time gets bend by the mass, for instance using a laser beam.$\endgroup$

## Fundamental Particle Dispersion Relationships

This method is to infer the mass of a fundamental particle from experimentally measured dispersion relationships.

A possible fourth quality to add to your list is that mass measures what I call a fundamental particle’s “stay-puttability”. This is actually the generalisation $E^2 = p^2 c^2 + m_0^2 c^4$ the mass-energy equivalence you cite in disguise. .

To look at this idea further, let’s think of the Klein-Gordon equation for a lone, first quantised particle, which each spinor component of something fulfilling the Dirac equation must fulfill:

$$\left\psi = 0\tag$$

Hopefully you can pick out $E^2 – p^2 c^2 – m_0^2 c^4=0$ from the unwonted way I’ve written the equation: recall $i\hbar\partial_t$ is simply the LHS of the general Schödinger equation, so that, by the Schödinger equation, $\hat$ and thus equivalent to the energy observable also $-i\hbar\nabla$ is the momentum observable. Maxwell’s equations can also be thought of as a kind of massless Dirac equation, so that the components of the potential four-vector also fulfill and we can think of the photon as being included in this discussion.

For pure energy eigenstates, $i\hbar\partial_t = \hbar \omega$ and if we Fourier transform into momentum space, we get from the *dispersion relationship* for the fundamental particle:

$$\omega^2 = k^2\,c^2 +\frac\tag$$

so that the group velocity is:

$$v_g = \frac\,\omega}\,k} = \frac}}\tag$$

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## Why Do We Use Kilograms Instead Of Newtons To Measure Weight In Everyday Life

What was the reason to use kilograms to measure weight instead of using newtons?

- 1Oct 2 ’14 at 3:54
- $\begingroup$Related: physics.stackexchange.com/q/43195/2451 and links therein.$\endgroup$ QmechanicOct 2 ’14 at 4:43
- $\begingroup$There is no difference in ordinary life, either. Nobody wants to buy five Newtons worth of beef, we all want half a kg .$\endgroup$Oct 2 ’14 at 5:09

The problem is that while mass is the same everywhere on earth, weight is not – it can vary as much as 0.7% from the North Pole to the mountains of Peru . This is in part caused by the rotation of the earth, and in part by the fact that the earth’s surface is not a sphere.

When you are interested in “how much” of something there is – say, a bag of sugar – you really don’t care about the local force of gravity on the bag: you want to know how many cups of coffee you can sweeten with it. Enter the kilogram.

If I calibrate scales using a reference weight, they will indicate the amount of mass present in a sample relative to the calibration . So if I have a 1 kg calibration weight, it might read 9.81 N in one place, and 9.78 N in another place but if I put the reference weight on the scales and then say “if you feel this force, call it 1 kg” – that is what I get. You can now express relative weights as a ratio to the reference.

So why don’t we call it “mass”? Well, according to , “weight” is a very old word,

## The Difference Between Mass And Weight

There are several differences between mass and weight.

Mass is an intrinsic property of matter. It doesnt change depending on where you measure it. It is a scalar value, which means it has magnitude, but no direction associated with it. The mass of an object is never zero. You measure mass with an ordinary balance on Earth or an inertial balance in space.

Weight depends on the effect of gravity, so it can change depending on where its measured. In the absence of gravity, weight can be zero. Because weight is a force, it is a vector. It has both magnitude and direction. You measure weight using a spring balance.

Mass is a property of matter. The mass of an object is the same everywhere. | Weight depends on the effect of gravity. Weight increases or decreases with higher or lower gravity. |

Mass of an object can never be zero. | Weight can be zero if no gravity acts upon an object, as in space. |

Mass does not change according to location. | Weight varies according to location. |

Mass is a scalar quantity. It has magnitude. | Weight is a vector quantity. It has magnitude and direction. The direction is toward the center of the Earth or other gravity well. |

Mass may be measured using an ordinary balance. | Weight is measured using a spring balance. |

Mass is measured in grams and kilograms . | Weight is measured in Newtons . |

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## Relative Weights On The Earth And Other Celestial Bodies

The table below shows comparative gravitational accelerations at the surface of the Sun, the Earth’s moon, each of the planets in the solar system. The âsurfaceâ is taken to mean the cloud tops of the gas giants . For the Sun, the surface is taken to mean the . The values in the table have not been de-rated for the centrifugal effect of planet rotation and therefore, generally speaking, are similar to the actual gravity that would be experienced near the poles.

Body |
---|

## Significant Figures In Calculations

When combining measurements with different degrees of accuracy and precision, * the number of significant digits in the final answer can be no greater than the number of significant digits in the least precise measured value*. There are two different rules, one for multiplication and division and the other for addition and subtraction, as discussed below.

**1. For multiplication and division: ***The result should have the same number of significant figures as the quantity having the least significant figures entering into the calculation*. For example, the area of a circle can be calculated from its radius using *A = r2*. Let us see how many significant figures the area has if the radius has only twosay, r = 1.2 m. Then,

*A* = *r*2 = × 2 = 4.5238934 m2

is what you would get using a calculator that has an eight-digit output. But because the radius has only two significant figures, it limits the calculated quantity to two significant figures or *A* = 4.5m2, even though is good to at least eight digits.

7.56 kg 6.052 kg + 13.7 kg = 15.208 kg = 15.2kg

Next, we identify the least precise measurement: 13.7 kg. This measurement is expressed to the 0.1 decimal place, so our final answer must also be expressed to the 0.1 decimal place. Thus, the answer is rounded to the tenths place, giving us 15.2 kg.

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## Vibrating Tube Mass Sensor

Measuring physical properties on the microscopic level presents challenges to scientists. One effective method for measuring microgram-sized biological samples in fluid is the vibrating tube mass sensor. First, the sensor determines the buoyant mass of an object by using the fluids density. After finding buoyant mass, absolute mass can be found by measuring the buoyant mass of the object in fluids of different densities. This affordable, portable sensor provides useful data for biomaterials such as embryos, cells and seeds.

## What Is Measurement In Physics

**Measurement** is the process of finding the length, size, or quantity of a substance. Since ancient times, people have used several ways to measure length. A physical quantity has to be measured with respect to some fixed quantity. A fixed quantity with respect to which a physical quantity is measured is called a unit. A unit is used as a standard of measurement. In early times, people used different body parts like hand span, cubit, and fathom to measure length.

Foot, pace, and yard are some other units of length based on body parts. However, these units are not reliable as the length of body parts varies from person to person. Therefore, people realized the need for

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Mass is “the amount of stuff” in an object. That is, the amount of atoms and molecules present. Mass in science, is measured in the metric system using units such as kilogram nwhich are a thousand grams, grams, centigrams , and milligrams . Mass is different from weight, Weight is a force. It depends on gravity pulling us toward the center of our planet . If we weighed ourselves on our bathroom scale and noted our weight and then took our scale with us to the moon, we would find that our weight was only one sixth as much there because the force of gravity is much smaller. However, because when we find mass, we use a procedure that compares our object with known mass, our mass would not change regardless of the amount of pull of gravity. This explains why astronauts did not change their size when they were on the moon even though their weight decreased considerably. Well, OK, that’s not exactly true. Their size changed just a little. They were temporarily a tiny bit taller because gravity was not pulling them down, compressing their spines a little bit. But that has nothing to do with the definition of mass.

## Why Do Scales Show Kilograms

Scales show Kilograms because that is what people understand best …

… but it is really just an **estimate of the mass** above them.

Scales should really show Newtons, but that might confuse people!

*Question: how many Newtons should the scales show when you stand on them ?*

- So the scales show an
**estimate of your mass**based on the force your body exerts on it. - And to find out how much force your body is exerting on the scales, multiply by 9.8 .

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## Types Of Mass And Weight

From the scientific point of view, understanding that *mass and weight* are magnitudes with which the matter contained in a body and the force exerted by gravity on it are respectively measured, the types of these that are best known and used are:

- Atomic mass: The mass of an atom.
- Molar mass: The mass of one mole of a substance.
- Molecular mass: The mass of a molecule of a substance.
- Inertial mass: That physical magnitude that indicates the resistance of a body to a change in speed.
- Body mass: It is the mass of a persons body.
- Atomic weight: It is the average mass of the atoms of an element.
- Molecular weight: It is the result of the sum of the atomic weights of the elements that make up a compound.

Related topics in our websites are:

## Difference Between Fundamental And Derived Quantities

There are certain physical quantities that cannot be explained in terms of other physical quantities. They are called *fundamental quantities*. They are the length, mass, time, electric current, temperature, luminous intensity and the amount of substance. The units used to measure the fundamental quantities are called *fundamental units *or *basic units* that is the fundamental units are the units of length, mass, time, electric current, temperature, luminous intensity and amount of substance.* *

The quantities which are derived from fundamental quantities are called *derived quantities*. *e.g. *volume, speed etc. The units of derived quantities are called *derived units* and are deducted from fundamental units. e.g. units of density, velocity, force, work etc.

For example, , and the unit is

Since the physical quantity velocity is derived from the fundamental quantities length and time, it is a derived quantity and its unit meter/second is a derived unit.

So, in short, we can write the difference between fundamental quantities and derived quantities as:

- Fundamental quantities are the base quantities of a unit system which are independent of other physical quantities.
- Derived quantities are the quantities which are derived from the fundamental quantities.

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## The International System Of Units

The kilogram is a cylinder of special metal about 39 millimeters wide by 39 millimeters tall that serves as the worlds mass standard.

So, In the SI system or the metric system of unit Kilogram is the standard unit of mass. Gram is also a smaller unit of mass used in metric units. There are prefixes that we can use if we want to measure a large amount of mass in metric units.

In this system of the unit of weight is Newton and is different from the unit used for measuring mass.

## Fun Facts About Mass And Weight

For centuries, there is a common misconception going on regarding mass and weight i.e they are most often thought to be the same physical quantities.

In other words, for the majority of people, there is no difference between them and i.e scientifically wrong. Hence, as a result, they are misused in everyday life.

For example, suppose you are in a local market and buying an apple from some local vendor. The net weight of the product is actually referred to as its mass.

In other words, what you are buying is in terms of its mass i.e is a kilogram. And, what you refer to it is its weight.

Thats it for this post. If you like this article, You can also find us on Mix, and Hey man, If you have come this far, do give us feedback in the comment section. It would make my day. Cheers!!!

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## Precision Of Measuring Tools And Significant Figures

An important factor in the accuracy and precision of measurements involves the precision of the measuring tool. In general, a precise measuring tool is one that can measure values in very small increments. For example, a standard ruler can measure length to the nearest millimeter, while a caliper can measure length to the nearest 0.01 millimeter. The caliper is a more precise measuring tool because it can measure extremely small differences in length. The more precise the measuring tool, the more precise and accurate the measurements can be.

## Importance Of Mass In Daily Life

The mass of objects is tremendously important in our daily lives.

- We work hard to reduce our mass when we are dieting. Less mass translates to less weight.
- Many manufacturers work to create less massive versions of items ranging from bicycles and running shoes to cars. When an object is less massive it has less inertia and is easier to move.
- Body mass index is a measure of body fat based on your weight in relation to your height. Fat is lighter than muscle, so a high BMI suggests that your body contains more fat and less muscle than it should.

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