Tag: force

STD 9

1. Universal law of Gravitation
2. Free fall
   1. To find out the value of g (acceleration due to gravity)
   2. Motion of the object under the influence of gravity
3. Mass
4. Weight
5. Thrust and pressure
6. Archimedes’ principle
7. Relative density

Gravitation

• It is the force of attraction between two objects in the Universe.
• The force of attraction is directly proportional to their masses.
• It is inversely proportional to the square of the distance between them.
• It is the weakest force in nature.

Gravity

• Gravitational force due to Earth is called gravity.

F = force between the two bodies

m1, m2 = masses of the two bodies

G = Gravitational constant = 6.67 x 10^-11 Nm^2/kg^2

Three Equations of Motion for free fall

• The acceleration due to gravity (g) is independent of the mass of freely falling body.
• It depends on mass of Earth and its radius.
  • Case-1 – When an object is falling freely towards the earth with an initial velocity (u) and after some time (t), its final velocity becomes v after travelling a height, h.

Mass and Weight

Mass (m)

• Mass of a body is the quantity of matter contained in it.
• Scalar quantity
• Has only magnitude and no direction.
• Remains constant.
• Does not change from place to place.
• Mass of the body is not equal to zero.
• Measured by physical and chemical balance only
• SI Unit: kg

Weight (w = mg)

• Weight is the force of an object.
• It describes how the object is attracted towards the centre of the Earth.
• F = ma = mg = w
• SI Unit is N (newton)
• It changes from place to place, because g changes from place to place.
• At the centre of the earth, g = 0.
• Mass of the body at the centre of the earth = 0

Relationship between 1 kg weight and newton (N)

Variation of value of g

Show that the weight of an object on the moon is about 1/6 th of the weight on Earth.

Send your solution.

[Q] A force 20 N acts upon a body whose weight is 9.8 N. Find out the mass of the body and its acceleration?