Physics and Life

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Physics and Life

• Cheng Cheung-tong (20)
• S.6B

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Content

• Introduction
• Light
• Reflection of Light
• Refraction of Light
• Rainbows
• Mirage
• Mechanics
• Why we need to stand BEHIND the yellow line
  before the train stopping?
• Why we need to tilt at an angle on a bike when we
  turn to lift or right?

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Introduction

• Technology plays a dominant role in our life,
  Physics is also involved in our life.
• Physics is science of matter and energy and how
  matter and energy can be described and modeled by
  mathematics.
• Physical science provides us with a way to
  predict behavior of a system by modeling it using
  math, then comparing the mathematical prediction
  to the experimentally observed results.
• Physics can be applied for energy, magnetism,
  greenhouse effect, medicine technology, etc.

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Light
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Reflection of Light

• The incident ray, the reflected ray and the
  normal all lie in the same plane.
• The angle of reflection is equal to the angle of
  incidence.

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Why do the blackboard also reflect light?

• Although black objects absorb most light which
  shines on them, a little light will also be
  reflected. In some cases, many light will be
  reflected in one direction by the blackboard due
  to its smooth surface.
• To solve this problem, we could use a blackboard
  which is a rough surface due to it can reflect
  the reflected light in different direction.

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Refraction of Light

• When a ray enters a block, the ray is bent.
• When it leaves the block, the ray is bent again.
• The ray keeps the same direction as before but is
  laterally displaced.

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Rainbow

• Rainbow always face the observer. As the observer
  moves, the rainbow moves.
• One can never get to the pot of gold at the end
  of the rainbow.

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Forming a Rainbow

• An observer sees red light coming from droplets
  of water higher in the sky, while droplets of
  water lower in the sky send violet light to the
  eye.

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Shape of Rainbow

• All of the droplets of water along the arc shown
  in the figure are equivalent.
• A rainbow would form a complete circle, not just
  an arc, if the ground didnt get in the way.

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Understanding Rainbow Geometry
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Double Rainbows

• The secondary rainbow displays colors in the
  reverse order
• Looking below about 42 degrees, the sky is
  relatively bright, and acts like a mirror to the
  sunlight.
• Above 42 degrees, the water absorbs most of the
  sunlight, and the sky is darker.

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Double Rainbows Explained

• One reflection in a primary rainbow droplet.

• Two reflections in a secondary rainbow droplet.

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Mirage

• Layer of air near the ground are hot, but layers
  higher up are cooler and denser, and have higher
  refractive indices. Light from the sky is
  gradually refracted more and more towards the
  horizontal. Then, total internal reflection takes
  place.

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Mechanics
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Why we need to stand BEHIND the yellow line
before the train stopping?

• While a train is traveling near you, the speed of
  air particles between you and the train increases
  due to the high speed of the train. Due to
  Bernoulli equation
• (Ppv2/2pghconstant)
• in hydrodynamics, the air pressure between you
  and the train decreases and the air pressure
  behind u increases. Then, the higher pressure
  behind you will push you towards the train which
  is traveling at a high speed.

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Why we need to tilt at an angle on a bike when we
turn to lift or right?

• Since we need to give a horizontal frictional
  force on the tires to produce a centripetal
  force. Then, this force maintains circular motion.

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End