Gluon, the so-called messenger particle of the strong nuclear force, which binds subatomic particles known as quarks within the protons and neutrons of stable matter as well as within heavier, short-lived particles created at high energies. Quarks interact by emitting and absorbing gluons, just as electrically charged particles interact through the emission and absorption of photons.

Raindrops take up the spherical shape due to the surface tension of water which is caused due to the   tendency  of water molecules to stick together. The spherical shape is having the least possible surface area due to which it can resist any of the external force in the atmosphere.

Work is said to be done when a force applied to an object moves that object. The SI unit of work is the joule (J)  . We can calculate work by multiplying the force by the movement of the object.  W = F × d

Positive Work

•  If a force displaces the object in its direction, then the work done is positive
  So, W=Fd
  The example of this kind of work done is motion of ball falling towards ground where displacement of ball is in the direction of force of gravity.

Negative work

• If the force and the displacement are in opposite directions, then the work is said to be negative.
  For example if a ball is thrown in upwards direction, its displacement would be in upwards direction but the force due to earth’s gravity is in the downward direction.

When the roads (dr tracks) are covered with snow then there is considerable reduction of frictional force between the tyres of the vehicle and the road (or between the track and the wheels of the train) which leads to the skidding of the vehicles. Thus, driving is not safe. When sand is thrown on the snow covered tracks or roads then the force of friction increases, so safe driving is possible .

A cricket player lowers his hands while catching a fast moving ball because this action helps in preventing injury to the hands. As a fast moving ball has a large momentum . In stopping (or catching) the ball its momentum is reduced to zero. Now , when a player moves back his hands on catching the fast ball , then the time taken to reduce the momentum of the ball is increased . Due to more time taken to stop the ball , the rate of change of momentum of the ball is decreased and hence a small force is exerted on the hands of player. So , they do not get hurt.

Weak Nuclear Force: This force appears only in certain nuclear processes such as the β-decay of a nucleus. In β-decay, the nucleus emits an electron and an uncharged particle called neutrino.This particle was first predicted by Wolfgang Pauli in 1931.

According to the law of equipartition of energy, for any dynamic system in thermal equilibrium, the total energy for the system is equally divided among the degree of freedom.

Kinetic Energy of a single molecule: KE = 1/2 mv². A gas in thermal equilibrium at temperature T, the average Energy is:

E_avg = 1/2 mv_x² + 1/2 mv_y² + 1/2 mv_z²  = 1/2KT + 1/2 KT + 1/2 KT = 3/2 KT

where K = Boltzmann’s constant. In case of a monoatomic molecule, since there is only translational motion, the energy allotted to each motion is 1/2KT. This is calculated by dividing total energy by the degrees of freedom:

3/2 KT ÷ 3 = 1/2 KT

To every action, there is always an equal and opposite reaction.

For example, when you hold the ball, a force acts on the ball (Action), and an equal and opposite force acts on your hand (Reaction).

• The gases following Boyle’s law, Charles’law and Avogadro law firmly are termed as anideal gas.
• From Boyle’s law we have  V ∝ 1/p (Constant T, n)
• From Charles’ law we have  V ∝ T (Constant p, n)
• From Avogadro’s law we have V ∝ n (Constant T, n)
• Combining them we get,  V ∝ nT/p
• or V = nRT/p 

pV = nRT ………………………… (IDEAL GAS EQUATION)

R =pV/nT

R= Gas Constant. It is same for all gases.

If  conditions at the two boundaries are same, then both even and odd harmonics are obtained. Based on this principle,  in an open organ pipe both odd and even harmonic are produced.

In Pth harmonic,

Total anti-nodes between two open ends = P + 1

Distance between two antinodes = λ / 2

l = P ( λ/2 )

λ = 2 I/P ----- (1)

n = V/λ  ----- (2)

Substituting (2) in (1) we get,

n = PV / 2 l

P = 1, 2, 3 ...

P = 1; n1 = V/2l -- This is 1st harmonic frequency

P = 2; n2 = 2 V/2l = 2 n1 -- This is 2nd harmonic frequency

Hence n1:n2 = 1:2

Similarly, n1:n2:n3:n4 ... = 1:2:3:4...

Hence proved, in an open organ pipe both odd and even harmonic are produced.

Angular momentum(L):-  It is an measure of the rotation of body, taking into account its mass , shape and speed.
 
L =  r ×​ p
where r is distance from the axis of rotation and the p is the linear momntum of the body.

Torque(τ): It is an moment of force i.e. tendency of a force to rotate an object about an axis.
We have shown that Newton's second law can be written as

ΣF = dp/dt.

where ΣF is the net force acting on a body.  Thus we can write

r ´ ΣF = r ´ dp/dt.

Since the net torque acting on a body is Στ = r ´ ΣF, and since we can add to the right hand side of the preceding equation the quantity dr/dt ´ p = 0 without changing its value, we can write

Στ = r ´ dp/dt + dr/dt ´ p = d(r ´ p)/dt.

We define angular momentum as

 L º r ´ p

The preceding equation then becomes

Στ = d L/dt,

which is the rotational analogue of Newton's second law as expressed at the top of this derivation.  (We note that 
like torque, which depends both upon the net force applied to a body and the point about which that torque is 
calculated, a body's angular momentum depends upon the net momentum of the body and upon the point about 
which its angular momentum is calculated.)