Physics and Life

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Physics and Life
S.6B Phy.Project LEI Kit-ha(7)
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Introduction
This is a power point designed to show a general
idea of what is physics, how is contemporary
physics related to our everyday live world, etc.
without having to go into the difficult technical
details of usual Physics courses. In writing the
power point, I have in mind the following goals
(i) To provide the readers a general feeling of
what is the foundation of contemporary physics
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(ii) To cover some basic concepts and knowledge
in Physics, including light, force, Newton's law,
etc. with everyday live examples illustrating the
importance of these basic knowledge, and (iii)
To provide the readers a general feeling of where
contemporary physics is heading. I wish the
readers would find that some of the physics
concept they read in this page are useful and
will develop further interests and appreciation
at the subject of physics.
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Light
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How can we see the objects?
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Reflection of Light
When light reflects off a surface, it follows
some rather basic rules which have been gradually
determined by observation. Consider the animation
to the left. A ray of light approaches a
reflecting horizontal surface at an angle of 45,
bounces from the surface, and leaves at an angle
of 45.
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Reflection of Light
We see an object when light from it entres our
eyes.Objects which are non-luminous are visible
only when they reflect light into our eyes.
Red ball reflects red light
Why can we see things by our eyes?
White ball reflects white light
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rainbow
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Rainbow can sometimes be seen when the sun shines
after a shower of rain. The sun behind you and
the rain in front of you.
Rainbow is produced when sunlight entres tiny
water droplets and is internally
reflected.Sunlight is dispersed into the seven
rainbow colours as it entres the droplets and
again as it leaves them.The dispersion is similar
to that produced by a prism.
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Refraction by a prism
A prism is a block of glass which have a
triangular base.When a narrow beam of light
passes through it, the beam is refracted and it
splits into all the colours of the rainbow.Since
different colours have slightly different
refractive indices in a meadium.The range of
colours obtained is called a spectrum.It
consists of red, orange, yellow, green ,blue,
indigo and purple.
White light is dispersed into seven colours by a
glass prism
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Bifocal spectacle lenses
People with both short sight and persbyopia often
wear bifocal spectacle lense.The upper part of
the lens is a diverging lens forseeing distant
objects whereas the lower part is a converging
lens for reading.
A concave lens
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The most commonly-seen type of lens is the convex
lens. This type of lens is often used for close
examination of small objects, such as rare stamps
or coins. Children often use such a lens to
concentrate sunlight to burn small pinholes in
pieces of paper. That result by itself shows the
power of concentrated light from the sun.
A converging lens
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Magnifing glass
It gives a magnified erect image of the
grasshopper within its focal length.The image is
virtual and lies on the same side of the lens as
the object.
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Force
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Let's have fun with physics!
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Roller Coaster
The roller coaster has no engine. The car is
pulled to the top of the first hill at the
beginning of the ride, but after that the coaster
must complete the ride on its own. You aren't
being propelled around the track by a motor or
pulled by a hitch. The conversion of potential
energy to kinetic energy is what drives the
roller coaster, and all of the kinetic energy you
need for the ride is present once the coaster
descends the first hill.
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Once you're underway, different types of wheels
help keep the ride smooth. Running wheels guide
the coaster on the track. Friction wheels control
lateral motion (movement to either side of the
track). A final set of wheels keeps the coaster
on the track even if it's inverted. Compressed
air brakes stop the car as the ride ends.
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Carousel
Carousels are not considered "thrill machines" by
any stretch of the imagination. Still, carousels
are as reliant on the laws of motion as their
more exciting cousins, the roller coasters. It's
theoretically possible that, allowed to spin out
of control, a carousel could gain enough speed so
that the riders would be thrown off. Thankfully,
runaway carousels are not the least bit common.
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Are some horses moving faster than others?With
all of its beauty and seeming simplicity, the
carousel is a delicate balance of motion and
forces. All of the horses move through one
complete circle in the same amount of time. The
horses on the outside of the carousel have to
cover more distance than the inside horses in the
same amount of time. This means the horses on the
outside have a faster linear speed than those at
the hub.
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Bumper Cars
Newton's third law of motion comes into play on
the bumper cars. This law, the law of
interaction, says that if one body exerts a force
on a second body, the second body exerts a force
equal in magnitude and opposite in direction on
the first body. It's the law of action-reaction,
and it helps to explain why you feel a jolt when
you collide with another bumper car.
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How do bumper cars work?Bumper car rides are
designed so that the cars can collide without
much danger to the riders. Each car has a large
rubber bumper all around it, which prolongs the
impact and diffuses the force of the collision.
The bumper cars run on electricity, carried by a
pole on the back of the car that leads up to a
wire grid in the ride's ceiling. This grid
carries the electricity that runs the car.
Electrical energy carried to the cars from the
grid is converted to kinetic energy, some of
which is converted to heat.
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Ending
After watching this power point, do you have a
deeper understanding of everyday life physics? Do
you find physics more funny? In fact, there are
still a lot of interesting things around us and a
lot of them cannot be explained yet. It will be
the role of you and me to look into them. Anyway,
hope you enjoy Physics!
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The End