### What is rigid body?

A system of large number of particles in which the distance between any two particles remains fix throughout the motion is called rigid body.

### Moment of inertia

Moment of inertia I is given by,

$$I = \Sigma m_i r_i^2$$

### Torque

If a force $$\vec{F}$$ acts at a point, whose position vector is $$\vec{r}$$; the torque due to force

$$\vec{\tau} = \vec{r} \times \vec{F}$$

### Angular displacement

Angular displacement is given by, $$\theta = \frac{s}{r}$$

### Angular velocity

Angular velocity is given by,

$$\omega = \frac{d\theta}{dt}$$

### Angular acceleration

Angular accceleration is given by,

$$\alpha = \frac{d\omega}{dt}$$

SI unit of angular acceleration is rad s-2. Its dimensional formula is [M0L0T-2].

### Angular momentum

Angular momentum is given by $$\vec{L} = \vec{r} \times \vec{p}$$ Where $$\vec{p}$$ is linear momentum of the particle and $$\vec{r}$$ is position vector of the particle.

### Relation between torque and angular momentum

Relation between torque and angular momentum is given $$\tau = \frac{d\vec{L}}{dt}$$

### Tangential acceleration

Tangential acceleration is given by,
$$a_T = \vec{\alpha}\times\vec{r}$$

Where $$\vec{\alpha}$$ is the angular acceleration and $$\vec{r}$$ is the position vector.

### Centripetal acceleration

Centripetal acceleration is given by,
$$a_c = \vec{\omega}\times\vec{v}$$

Where $$\vec{\omega}$$ is the angular velocity and $$\vec{v}$$ is the linear velocity.

### How many fundamental and supplementary units in SI?

In SI, there are seven base ( fundamental ) units and two supplementary units.
Base unit

Physical quantity

Unit

Symbol

Mass

Kilogram

kg

Length

Metre

m

Time

Second

s

Temperature

Kelvin

K

Electric current

Ampere

A

Luminous intensity

Candela

cd

Quantity of matter

Mole

mol

Supplementary units

Physical quantity

Unit

Symbol

Plane angle

Solid angle

sr

Conversion factor
Conversion of length

1 centimetre = 10-2 metre
1 millimetre = 10-3metre
1 micrometre = 10-6metre
1 nanometre = 10-9 metre
1 angstrom= 10-10 metre
1 fermi = 10-15 metre
1 kilometre = 103 metre
1 austronomical unit = 1AU=1.496 × 1011 metre
1 light year = 1 ly = 9.461 ×1015metre
1 mile = 1.609 ×103 metre
1 yard = 0.9144 metre
1 inch = 0.0254 metre

Conversion of time

1 mili second= 10-3 second
1 micro second = 10-6 second
1 neno second = 10-9 second
1 hour = 60 minute = 3600 second
1 day = 24 hours =86400 second
1 year = 365 day = 3.156× 107 second
1 sec = 10-8second

Conversion of mass

1 gram = 10 -3 kg
1 quintal = 100 kg
1 tonne = 1000 kg
1 slug = 14.59…

### What is the Universal law of gravitation?

Force of attraction between two masses $$m_1$$ and $$m_2$$ is given by, $$F = \frac{m_1 m_2}{r^2}$$ Where, r is the distance between two masses $$m_1$$ and $$m_2$$. G is a constant, called the Universal gravitational constant. That is called Universal law of gravitation. Acceleration due to gravity ( variation formula ) If a body is falling freely, under the effect of gravity, then the acceleration in the body is called acceleration due to gravity. Variation in acceleration due to gravity with height Acceleration due to gravity at a height h above the surface of earth is, $$g' = g (1 - \frac{2h}{R_e})$$ Where, Re is the radius of the earth. g is the acceleratin due to gravity. Variation in acceleration due to gravity with depth Acceleration due to gravity at a depth d below the surface of earth is, $$g' = g (1 - \frac{d}{R_e})$$ Where, Re is the radius of the earth. g is the acceleratin due to gravity. Variation in acceleration due to gravity with rotatio…

### Differentiation formula

Fomulae of Differentiation d⁄dx (c) = 0   Where c is constant.d⁄dx (cx) = c   Where c is constant.du⁄dt = du⁄dx ⋅ dx⁄dtd⁄dx (u+v) = du⁄dx + dv⁄dxd⁄dx (uv) = u dv⁄dx + v du⁄dxd⁄dx ( xn ) = n xn-1  Where n is real number.d⁄dx un = n un-1du⁄dx   Where u is function of x.d⁄dx sin x = cos x d⁄dx cos x = -sin x d⁄dx tan x = sec2 x d⁄dx cot x = - cosec2 x d⁄dx sec x = tan x sec x d⁄dx cosec x = - cot x cosec x d⁄dx loge x = 1⁄xd⁄dx loge u = 1⁄udu⁄dxd⁄dx ( ex ) = exd⁄dx ( eax ) = a eaxd⁄dx sin ax = a cos ax d⁄dx sin (ax+b) = a cos (ax+b) d⁄dx cos ax = - a sin ax d⁄dx cos (ax+b) = - a sin (ax+b)