Our Universe: GRAVITATION
A- The earth is stationary and is at the centre of the universe, with the sun, the moon,
planets and stars revolving the earth.
2. What is Heliocentric theory?
A- All the planets revolve in a perfect circle with the stationary sun at the centre of these
3. What is acceleration due to gravity?
A- 1.The Uniform acceleration produced in a freely falling body due to gravitational pull of
the earth is called acceleration due to gravity.
2. It is denoted by (g)
4. Define the mass of a body?
A- The total quantity of matter contained in a body is defined as its mass.
5. Define the weight of a body.
A- The weight of a body is the force with which it is pulled by the earth towards its centre.
6. State Hooke's law?
A- According to Hooke's law "Stress is directly proportional to strain when a body is in
7. Calculate the gravitational force on a stone of mass 10kg?
A- Acceleration due to gravity (g) = 9.8m/sec2
mass of the stone, m=10kg
The gravitational force on the stone,
F = mg = 10 × 9.8 = 98 newton.
8. Define 1 kg wt?
A- The gravitational force acting on a body of mass 1kg is called 1kg wt.
9. What is the relation between 'g' and 'G'?
stone of mass. 10kg.
A- Newton's Universal law of gravitation states ''that every body in the universe attracts
every other body with a force which is directly proportional to the product of their masses
and inversely proportional to the square of the distance between them"
Problem: We know that F = mg
= F = 10 × 9.8 = 98 N
2. What are the various factors that effect on the value of acceleration due to gravity
A- The various factors that influence the value of 'g' are
1. Shape of the earth
a) At poles
b) At equator
2. Height (Altitude)
4. Local Conditions
3. Why is the weight of a body not the same at poles and equator?
A- The weight of a body W=mg. So it depends on acceleration due to gravity. It is directly
proportional to acceleration due to gravity. As the acceleration due to gravity is not same
at the poles and equator, the weight of a body is also not the same at the poles and the
4. Why does the weight of a body differs from one place to another place?
A- The weight of a body w=mg. It means the weight of a body is directly proportional
acceleration due to gravity. As the value of acceleration due to gravity 'g' changes from
place to place, the weight of a body also changes from place to place.
5. What is gravity meter? Give examples?
1. The value of g at a given location is slightly affected by geological deposits
concentration of massive concrete building and topography of the region
2. So,a sensitive instrument is used to measure such small changes in the value of g at a
3. This instrument is called gravity meter.
4. Examples: Gulf gravity meter and Boliden gravity meter.
6. Differential between mass and weight of a body.
- The following are the differences between mass and weight.
A. Newton's law of universal Gravitation: Everybody in the universe attracts every other
body with a force which is directly proportional to the product of their masses and
inversely proportional to the square of the distance between them. The force acts along
the line joining the two bodies.
Let the masses of any two bodies be m1 and m2 and they are separated by distance ''r''.
The gravitational force of attraction between the two bodies is directly proportional to
the product of their masses.
F - m1m2.................(1)
The Gravitational force of attraction between the bodies is inversely proportional to the
square of the distance between them.
F a 1/r2 .................. (2)
From (1) and (2)
Where G is the proportionality constant and is called ''Universal Gravitational Constant"
2. Explain the change in the value of 'g' as we go from the surface of the earth to deep
1. 'g' value decreases from the surface of the Earth to deep inside.
2. The reason for the decreases in 'g' value is decrease of effective mass of the Earth.
3. The effective mass of the earth is given by the equation Where p is the average density of the Earth.
4. From the above equation, the effective mass M influencing the body decreases inside the
mine as effective r decreases.
5. If g is acceleration due to gravity at a depth ''d'' inside the mine and g is acceleration due
to gravity on the surface, then the relation between them is given by
6. Thus at the centre of the earth (d=r) so"gd'' value becomes zero at center of earth.
3. Derive the relation between acceleration due to gravity and Gravitational
- Let 'G' and 'g' be universal Gravitational constant and acceleration due to gravity.
Suppose a stone of mass 'm' is dropped from a distance 'r' from the centre of the Earth
of mass M, then the force exerted by the Earth on the stone is given by the Universal law
of Gravitation as.
F= G Mm/r2 .........(1)
This force produces acceleration 'g' on the stone but according to Newton's second law
F = mg ............(2)
Hence g=G M/r2
from the above equation, g is independent of the value of the mass of the stone.
4. Describe an experiment to determine the weight of a body?
Aim: To determine the weight of a body.
Apparatus: An extensible spring, pan, weights, stand, metre scale, plasticine.
Method: Suspend the spring to the stand. Attach a pan to the lower end of the spring.
Also fix a pin at the lower end of the spring. Also fix a pin at the lower end of the spring
at right angles to the spring by means of a little plasticine.
The horizontal pin serves as a pointer. Fix the metre scale vertically so that the pointer Can more over the scale.
Record the reading of the pointer on the scale (lo) initially. Add a 10 gram weight of the scale pan. Note the reading of the pointer (l1). Record the readings by adding 10 gramseach time.
Plot a graph between stretching ((l – l0) against force (F). This graph is a straight and is called Calibration graph for the spring.
Force Balance Readings (m) Mean Length Extension of the spring (gm.wt) Loading Unloading l (cm) (l – l0)
Now place the body on the pan and note down the extension (l-lo).
Locate the point of (l-lo) On Y-axis And Read The Corresponding X-ordinate. This gives the weight of the body.
a) Circular Orbit
b) Elliptical Orbit
c) Rectangular Orbit
2. The law of Gravitation ( )
a) applies only to large bodies such as planets and stars
b) accounts for all known forces
c) holds only in the solar system
d) holds everywhere in the universe.
3. The weight of 400g stone is ( )
c) 3.92 N
d) 3920 N
4. The distance of the Moon and from the Earth is about? ( )
a) 3.85 × 105 km
b) 3.85 × 105 m
c) 385 × 105 km
d) 385 × 105 m
5. The Unit of force in S.I. system is ( )
d) Newton Metre
6. The units of gravitational constant ( )
b) Nmkg – 2
d) Nm–2 kg–2
7. The Gravitational force of attraction between any two bodies is ( )
8. All bodies large or small falls on the ground with the same ( )
9. As we go from the equator to the poles, the values of 'g' ( )
a) remains the same
d) decreases up to altitude of 45°
10. Value of 'g' on the Earth is ( )
a) 9.8 ms–2
b) 1.67 ms–2
c) 98 ms–2
d) 167 ms–2
11.The relation between g and G is ( )
a) G = 9
b) g = GM/r2
c) g = Gr2
d) None of these
12.Acceleration due to gravity at a height 'h' from the surface of the Earth is ( )
13.Which of the following instrument used to measure small changes in the value of 'g'? ( )
a) Boliden Gravity Meter
14.1kg Weight = ( )
a) 9.8 ergs
b) 9.8 joule
c) 9.8 kg
d) 9.8 newton
15.Which one of the following is changes with change in place? ( )
c) mass and weight
II. Fill in the blanks
1. Ptolemic theory is also known as _______
2. Copernicas theory is known as ________
3. The weight of 500g stone is _______ N
4. Units of Universal Gravitational constant G are _____
5. Units of acceleration due to gravity are ______
6. Acceleration due to gravity is independent of _______
7. Acceleration due to gravity maximum at earth's______ the and minimum at the ______
8. Mass of a body is ______ any where in the Universe.
9. Mass of a body changes from _____ to place.
10.The distance of the moon from the earth is about ______
11.According to Newton's second law of Motion F = mass × ______
12.Acceleration due to gravity is independent of the value of the _____ of the stone.
13.Acceleration due to gravity at the centre of the Earth _____
14.____ law helps in the determination of the weight of the body.
15.The 'g' value of sun is _____
16.The weight of the body is the ______ of the earth's gravity acting on it.
17.In formula2 G stands for ______
III. Match the following
Fill in the blanks
1. Geocentric Theory
2. Heliocentric Theory
6. mass of the bodies
7. poles, equator
9. place10. 3.85 × 105km
14. Hooke's Law
16. Force of attraction
17. Universal Gravitational Constant
Match the following
About The Author
Praesent nec tortor quam. Quisque ac malesuada augue. Sed dignissim gravida odio ut bibendum. Cras fermentum euismod turpis. Nunc nec diam ante, et faucibus ipsum. Etiam imperdiet mattis elit et molestie. Nulla feugiat mollis leo vel egestas. Pellentesque convallis