Hey friends, we all know that Physics works all around us. Even in our celebrations of Diwali. When we talk about Diwali, first thing that comes to our mind is “Fireworks”.

Do you know there is Science while we fire the crackers? Just think.

Yes… it is. Laws of Physics applied in that also.

Let us see few…

  1. ROCKET:

While we burn it, it goes in upward direction and then burst.

  • So, which law brings it up the sky? Its law of conservation of momentum or Newton’s 3rd law of motion. i.e. action and reaction are equal and opposite.
    When it is lit, combusted gas comes out in the downward direction. The force of exhaust gas gives the thrust to rocket in upward direction.
    Before firing: Rocket in state of rest, airspeed is zero.
    When fired: Thrust increases from zero and weight reduces slightly as the fuel burns.
    When Thrust is greater than weight, Net force is positive in upward direction. And rocket accelerates in the sky. Its velocity increases.

    • In short, after igniting the Rocket, it catches the fire. And due to the gas exhausts in downward direction, force will be in upward direction, which lifts the rocket up.
    • Space Rocket, which we launch and even a balloon left in air without tying work of the same principle.
  • Another, when it is kept with some tilt, it progresses with projectile motion. (Caution: Don’t do it!)
  • Doppler Effect: when rocket lifts up, a whistling sound is heard and as it moves away, we can feel the change in sound’s intensity and frequency due to the relative motion.
  • Exercise: Calculate the accelerating force on the cracker rocket, if it ejects gases at a rate of 200 g/s with a velocity 500 m/s. (Hint: use the formula of force for variable mass system)
    1. 100 dyne
    2. 1 N
    3. 10 N
    4. 100 N
  2. CHAKHRI (ground spinner or Chakkar, Firki):

    It consists of a propellant (gun powder) filled tube wound in the form of a spiral. When ignited, the Chakkar starts rotating with an ever increasing angular speed.
    When we ignite it, Torque is applied to the cracker as it is wound in a spiral shape; a tangential force is being applied.
    After burning out all the fuel/chemical, still it spins due to the conserved angular momentum.

    Think: what happens if it is placed on a very smooth surface?
  3. SPARKLERS:

    when it sparkles, its temperature is very high (~ 1000-1600 °C). But still we cannot get harm due to the sparkles that fall on our body. Why such?
    The reason is hiding in the quantity, Thermal capacity. As the mass of the tiny sparkle is very less, it carries very less thermal capacity according to the formula (m x S), where S is specific heat of the material.

  4. ATOM BOMB:
  5. Thermodynamics works behind it. In an atom bomb, a combustible material is tightly packed in the cover.
    When it is ignited, the temperature inside the chamber is increasing. And according to Gas law PV = nRT, pressure increases very high. Due to this increased pressure, it burst out with very strong sound.This is the only reason, a bigger bomb blasts with high intensity compared to a smaller one.
  6. COLORED FIREWORKS:

    Different colors from crackers are visible just due to the emission spectra of  elements. Emission Spectra is nothing but the transition of electrons from higher state to a ground state. Color depends on the energy differece of these states and corresponding to that, the element emits the radiation of particuler wavelength, which ultimately displays the color.

    Here is the list of different chemicals which have been used to produce different colors:

    1. Sr – red
    2. Ca – orange
    3. Na – yellow
    4. Ba – green
    5. Cu – blue

    Enjoy the crackers carefully and of course with Science.