Mandela's Blog

Solar cars

2008-11-27T03:01:00.000-08:00

Solar cars combine technology typically used in the aerospace, bicycle, alternative energy and automotive industries. The design of a solar vehicle is severely limited by the energy input into the car (batteries and power from the sun). Virtually all solar cars ever built have been for the purpose of solar car race (with notable exceptions).

Like many race cars, the driver's cockpit usually only contains room for one person, although a few cars do contain room for a second passenger. They contain some of the features available to drivers of traditional vehicles such as brakes, accelerator, turn signals, rear view mirrors (or camera), ventilation, and sometimes cruise control. A radio for communication with their support crews is almost always included.

Electrical and mechanical systems

The electrical system is the most important part of the car's systems as it controls all of the power that comes into and leaves the system. The battery pack plays the same role in a solar car that a petrol tank plays in a normal car in storing power for future use. Solar cars use a range of batteries including lead-acid batteries, nickel-metal hydride batteries (NiMH), Nickel-Cadmium batteries (NiCd), Lithium ion batteries and Lithium polymer batteries

Races

The two most notable solar car races are the World Solar Challenge and the North American Solar Challenge, overland road rally-style competitions contested by a variety of university and corporate teams.

The World Solar Challenge features a field of competitors from around the world who race to cross the Australian continent, over a distance of 3000 km. The increasingly high speeds of the 2005 race participants has led to the rules being changed for future solar cars starting in the 2007 race

Force

2008-11-26T19:43:00.000-08:00

A force is a push or a pull. It is also a vector; It has size and direction. There are three common forces.

Contact force is a force applied by touching.
Gravity is the force of attraction between two masses.
Friction is the force that resists motion between two surfaces pressed together.

Balance Force

These humans in the pictures give 2N It is balance force.
Balance force is the net force that acting on a object is 0

Unbalance Force

These humans in the pictures give 2N In the left picture, it is unbalance force.
Unbalance force is the net force that acting on a object isn’t zero

Touch Force

We called touch force
because we give force with touch the object
The picture shows the touch force from the cue ball
(Note. The cue ball didn’t show here)

Untouch (Field) Force

We called untouch force
because we give a force without touch the object
For example :

Weight

Magnetic

Pressure

2008-11-26T18:11:00.000-08:00

Pressure
is the force divided by the area on which it is exerted.
Pressure at sea surface give 101300 Pa or 760 mmHg or 1atm.
Higher a place from sea surface, smaller its atmospheric pressure then at sea surface.

Manometer

Measuring device of air pressure called Manometer

Pressure of Gas Law
There are three law about air pressure :

Boyle’s Law

Charles’ Law

Combined Law

Boyle’s Law
Boyle’s law states that for a fixed sample of gas at constant temperature, the volume of the gas varies inversely with the pressure.
PV=constant, or P1V1 = P2V2
If you make the volume bigger, so the pressure bigger if the temperature is constant.

Charles’ Law
At constant pressure, the volume of a given mass of an ideal gas increases or decreases by the same factor as its temperature increases or decreases.
V1/T1= V2/T2

Combined Law
Based on the Boyle’s and Charles’ Law, so

When,
P is the pressure.
V is the volume.
T is the temperature

Application Drinking Straw

When someone drink from drinking straw,
he/she make the straw pressure lower than
air pressure and make water pushed into the straw

Speed

2008-11-26T03:39:00.000-08:00

Velocity and Speed

Speed is equal to distance traveled divided by time taken
Velocity is equal to displacement divided by time taken.
Velocity is speed with a direction. If we calculate an object velocity, we have to think about its direction too.

Calculating the speed

The way to calculating speed is

v = d : t

d = v x t

The unit of distance in SI is meter, and the Unit of time is second; therefore the unit of speed is meter per second (m / s).
The difference between velocity & speed is only in direction. The unit of velocity is same as speed, m / s

The Question of Speed

An athlete made his world record of 10 km within 20 minutes. What was his speed?

Solution:

Known:

Distance, d = 10 km = 10.000 m

Time,

t = 20 minutes = 1200

Asked:

speed, v = ? use equation v = d / t

Result:
v = d / t = (10.000 m) / (1200 s) = 8.33 m / s

Refraction

2008-11-24T05:32:00.000-08:00

Refraction

Refraction is a bend event of direction light transmission from one medium to the others which have different density. In our daily life we often see the light refraction, such as a pencil dipping into a glass containing water, the pencil will look like bent.

Law of Light Refraction

According to Willebord Snellius, the light which comes from one medium to the other mediums will get the light refraction:

the incident ray, normal line, and the refraction ray located at one area and cross at one point.
The incident ray from the less dense medium to the more dense medium will be refracted close to the normal line, and the incident ray from the more dense medium to the less dense medium will be refracted far from the normal line.

Medium Refraction Index

Refraction Index is the comparison value between ray incident projection and ray refraction projection in refracting path. Medium refraction index is various, depend on to the kind of the medium its self.Refraction index can be calculated as
(n)= C/V
C is ray incident projection and V is ray refraction.

Deviation Angle

The refraction by prism will make deviation angle

δ = deviation angle

i = incident angle from air

β = refraction angle prism

r = refraction angle in air

Mirror

2008-11-24T04:41:00.000-08:00

The kinds of Mirror

Plane Mirror
Concave Mirror
Convex Mirror

Light Reflection of Plane Mirror
The characteristics of Plane mirror,

Virtual / not real
The object distance to the mirror is equal to the distance of shadow to the mirror (s=s’)
The height of the object is equal to the height of the shadow (h=h’)
The magnifying of the shadow (M) is equal to 1 (M=s’/s = h’/h = 1
The left side of object becomes the right side of the shadow and vice versa

Light Reflection of Concave Mirror
There are 3 special rays,

The incident ray that is parallel to the focal axis is reflected to the focus point
The incident ray which comes through the focus point is reflected parallel to the focal axis
The incident ray which comes through the center point of curvature mirror will be reflected back to the curvature mirror center point

Light Reflection of Convex Mirror
There are 3 special rays,

The incident ray which is parallel to the focal axis will be reflected as if from the focus point.
The incident ray which goes to the focus point will be reflected parallel to the focal axis.
The incident ray which goes to the curvature focus point mirror will be reflected as if from the curvature focus point.

LIGHT

2008-11-17T20:43:00.000-08:00

Is electromagnetic wave which can transmit without medium. Light can transmit in vacuum room. In the past, light used to be thought as particle lines transmitted by light sources. This idea was conveyed by Newton. But this idea was perfected by Christian Huygens, which stated that light is electromagnetic wave.

The Speed of Light

In vacuum is 3 x 108 m/s. The first person who wants to measure the speed of light is Galileo. However, he failed in the experiment. And the next, the experiment of measuring speed of light was done by Jean Foucalt (a France). He was successful to measure the speed of light up to 300.000 km/s. But the person who was successful to measure speed of light in high accuracy is Michelsen (an American). He measure the speed of light is 2,99729 x 108 m/s (made to be 3 x 108 m/s).

Light Reflection

Diffuse Reflection = A Reflection which occurs when a light goes to an unflat area. The light will be reflected irregularly and spreads in any directions.

Regular Reflection = Regular reflection is reflection which occurs at reflecting area which is flat. The lights that are reflected are still parallel or regular.

Law of Light Reflection
The light which goes to an area will get light reflection law, according to Snellius;
Incident ray, normal line, and reflection ray located at one plane area
Incident angle (i) is equal to reflection angle (r)

Pulleys

2008-11-17T19:36:00.000-08:00

FIXED PULLEY

A fixed or class 1 pulley has a fixed axle. That is, the axle is "fixed" or anchored in place. A fixed pulley is used to change the direction of the force on a rope (called a belt). A fixed pulley has a mechanical advantage of 1.
The total weight on this pulley is 1,0 N

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MOVABLE PULLEY

A movable or class 2 pulleys has a free axle. That is, the axle is "free" to move in space. A movable pulley is used to multiply forces. A movable pulley has a mechanical advantage of 2. That is, if one end of the rope is anchored, pulling on the other end of the rope will apply a doubled force to the object attached to the pulley.
The weight of the object is 1 N
The weight of the pulley is 0.3 N
The total weight of this pulley is 1 + 0.3 = 1.3/2
= 0.65 N = 0.7 N

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COMPOUND PULLEY

A compound pulley is a combination of a fixed and a movable pulley system. Compound pulley has a mechanical advantage according as many as the pulley. And for this pulley the mechanical advantage is 3.
The weight of the object is 1.5 N
The weight of the pulley is 0.3 + 0.8 = 1.1
The total weight of this pulley is
1.5 + 1.1 = 2.6 / 3
= 0.866 N
= 0.87 N

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Physic Experiments

2008-11-13T20:39:00.000-08:00

for
Junior
High
School

SPITING Light

What you need

To do this activity you will need:

sunlight
a piece of card with a one millimetre wide slit cut into the middle

a straight-sided glass filled with water

a sheet of white A4 paper.

What to do

Fill a straight-sided glass with water and tape the card onto the side of the glass.

Place the white sheet of paper close to a window where sunlight is entering.

Stand the glass on the paper with the slit facing towards the Sun.

The sunlight should pass through the slit and split into its colour components as it enters the glass. The colours should appear on the paper.

What's happening?

White light is a mixture of many different colours. Sir Isaac Newton proved this more than 300 years ago when he directed a beam of sunlight through a slit and prism in a darkened room in 1666.

The prism bent, or refracted, the white light so that it fanned out into a rainbow (spectrum) of colours.

Splitting light using prisms is known as spectroscopy. Each chemical element has a unique signature when its light is split up.

Astronomers use spectroscopy to determine what planets and stars are made of by examining their light.

Static ELECTRIC

What you need ???

To do this activity you will need:

a balloon

a woollen jumper or clean hair

torn up paper

pieces of Styrofoam

salt.

What to do ???

Spread out the torn-up pieces of paper, small pieces of Styrofoam and salt on a table.
Blow up the balloon and rub it on a woollen jumper or on your hair (your hair needs to be clean and dry).
Hold the balloon near the things on the table. What happens?

What’s happening ???

Everything around us is made of tiny particles called atoms. Circling around atoms are even smaller particles called electrons. When you rub things together, some electrons rub off onto the other object – this creates an electric charge.

When you rub the balloon, electrons from the jumper move onto balloon. The balloon becomes ‘negatively charged’ because it has extra electrons. On the other hand, the jumper becomes ‘positively charged’ because it has lost some electrons.

The more you rub the balloon, the more static electricity you build up. The objects on the table react to the charge by becoming attracted to the balloon. After a while the balloon loses its charge, and the objects drop off.

Have you ever heard the phrase ‘opposites attract’? Things that have opposite charges attract each other better than a charged object attracting a neutral object (one with no charge). So when you rub the balloon with the jumper, there is a stronger attraction between the (positive) jumper and the (negative) balloon than between the (neutral) paper and the (negative) balloon.

Static electricity is different to the electricity used to power your lights at home – static electricity has no currents running through it and doesn’t use wires.

Applications

Photocopiers work by using static electricity. Inside a photocopier is a special drum that has a positive charge that can be affected by light.

When you copy an image, a light beam moves across the page. The light reflects off the white areas of the paper and hits the drum below. Where light hits the drum, it neutralises the positive charge. Dark areas on the paper don’t reflect light back onto the drum, so these areas of the drum remain positively charged.

Negatively charged black particles called toner are spread over the drum and stick to the positively charged areas of the drum. Positively charged paper is then passed across the drum, picking up the toner. Heating and pressing the paper fuses the toner to the paper, creating a copy of the original image.

Adapted from: http://www.csiro.com