Results for physics

## Physics: Fundamental, derived quantity, Units, and Dimensions.

August 16, 2019
Fundamental Vs Derived quantity

Fundamental quantities

These are independent quantities with units. The dimension of a physical quantity indicates how it is made up in terms of S.I base quantity.

In other words, the physical quantities is said to have been expressed in terms of fundamental units [Length (L), Mass (M), Time (T), kelvin (k), mole etc].

Quantity Dimension

length         L
Mass          M
Time           T
Kelvin        K
Mole          m

Derived quantities:

These are obtained by some simple combinations of the fundamental quantities and units.

They are thus, dependent on the fundamental quantities and units. Example of the derived quantities, their derivation and their units are summarised in the table below:

 Derived quantity Derived unit Dimension Area  (length x breadth) m^2 L^2 Volume(length x breadth x height) m^3 L^3 Density (Mass/volume) kg/m^3 M/L/L Velocity (Displacement/time) m/s L/T Acceleration (Velocity/time) m/s/s L/T/T force (Mass x acceleration Newton (N) ML/T/T Energy & work (force x distance). joules ML^2/T/T power (work/time) joules/s ML^2/T/T/T Momentum (Mass x velocity) kg m/s ML/T Pressure  (force/area) N/m^2 ? Frequency (no of oscillation/time) 1/s 1/T

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Example

What is the dimension of EMF?

EMF(Electromotive Force) is a derived quantity. It is work done by the chemical force to move unit positive charge from negative terminal to positive terminal of the battery.
EMF = Workdone / charge
Work=Force * displacement
=MLT^-2 * L =ML^2T^-2
Charge=Current * time
=IT
Now,
Dimensional formula of
EMF=Work/charge
=ML^2T^-2 / IT
=ML^2T^-3I^-1

Exercise:

What is the dimension of pressure?

Solution
Watch how to derive the dimension of Pressure.

Conclusion

A  derived quantity is derived from fundamental quantity, simple and short. I hcomments article was helpful. If you have any questions or comments, please don't hesitate to write it in the comments section. All comments are appreciated.

Physics: Fundamental, derived quantity, Units, and Dimensions. Reviewed by uyi osamudiamen Lucky on August 16, 2019 Rating: 5

## Physics: Mass and Weight, relationship, differences and related questions

August 16, 2019

### Mass

A mass of a body is the quantity of matter contained in that body. It is a scalar quantity I.e. it has magnitude but no direction. The unit of mass is kilogramme (kg).

### Weight

This is a measure of the force of gravity of the earth on a body. It is a gravitational pull of the earth on any body towards its centre. It is a vector quantity I.e. it has magnitude as well as direction. The unit of weight is Newton (N).

### Relationship between mass and Weight

Weight of a body = Force
Force = mass of body x acceleration due to gravity
I.e. W = F =  mg
m = W/g

For example:

Find the weight of a ball if the mass of the ball is 10kg and the acceleration to gravity is 10m/s2.
Solution
W = mg
W = 10 kg x 10 m/s2
W = 100N

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### Difference between mass and Weight

1)  Mass is the quantity of matter contained in a body While weight is the measurement of the force of gravity on a body.
2) Mass is a scalar quantity while weight is a vector quantity.
3) The S.I. unit of mass is kilogramme while the S.I. unit of weight is Newton.
4) Mass of the body is constant throughout the universe, while weight varies from place to place in the universe.
5) The instruments  used to measure mass can be beam balance, lever balance or chemical balance, while the instrument used to measure weight is spring balance.

### Read on the Equations of motionMass and weight - on moon    An astronaut on earth weighing 980N and mass of 100kg (acceleration due to gravity on earth is 9.8m/s^2).

Weight on Earth: 100kg x 9.8m/s2 = 980N.

Weight on Moon: 100kg x 1.622 m/s2 = 162.2N.

Observation
The same astronaut on the moon would weigh 162.2N and have a constant mass of 100kg (acceleration due to gravity is 1.622m/s^2)

### Related Questions

1)  The mass of a rock on the Earth is 2.0 kg. What is the mass of the rock on the Moon?
A) 1.7
B) 2.0
C) 3.5
D) 20.0

2) Why is weight not equal everywhere?
A) Because of altitude.
B) Because of the varying mass other planets when compared with earth.
C) Because of force of gravity
D) All of the above
E) None of the above

3) An astronaut of mass 40 kg jumped out of the rocket after it had landed on Jupiter.  The astronaut took 0.40 s to drop for 2.0 m. What was the weight of the astronaut on Jupiter?
A) 500
B) 1000
C) 800
D) 2000

4) A student's weight on Earth is 100 pounds. If this student went to the Moon,what  would he weigh?
A) more
B) less
C) the same

Do you know any of the answers? If so share it or ask for it. Do you have any other mass and Weight related questions? Ask it and I will be happy to answer it or send you a detailed solution. Responses are within 24hrs.

Physics: Mass and Weight, relationship, differences and related questions Reviewed by uyi osamudiamen Lucky on August 16, 2019 Rating: 5