Short notes and tips for Physics SPM

-In this chapter, you are required to know what is the differences between Base quantities and derived quantities

-between vector and scalar quantity.

-How to use measuring instruments and their sensitivity

-How to identify errors(Systemic and Random)?

-Accuracy, consistency and sensitivity.

-Steps involve in scientific investigation.


BASE AND DERIVED

BASE Quantities

• In colours, you have learn about base colours, which are red, blue, and yellow. Why do we called them base colours? Because they can't be form from combining any colours. In other words, they are the basic of all colours.
• This applies to base quantities in physics as well. Base quantity cannot be formed from any other quantities.
• Base quantities are MaTiLET, Mass(kilogram/kg), Time(second/s), Length(meter/l), Electric current(ampere/A), Temperature(Kelvin/K).
  

DERIVED Quantities

• Just like colours, when you combine Blue and Red, it will turn Purple. When you combine length and time, it will become speed. However, in colours, you mix them up with a brush, in physics, physicists mix the base quantities with mathematics notation such as times, divide, power, exponent, logarithm and many more. But be thankful, they won't ask you on these except for times and divide.
• So, in your level, the definition for derived quantity is quantity derived from a combination of base quantities through multiplication and division.
• Examples of derived quantities are area(l x l), volume(l x l x l), density(kg/l x l x l), speed(l /s) and many more.

So, the tips of memorising derived quantities is by memorising base quantity(there is only 5 base quantities in you syllabus). Anything that is not a base quantity must be a derived quantity.



SCALAR AND VECTOR

SCALAR(in other word, the value do not have negative or absolute values).

• Scalar(in Latin, it means amount) quantity mean quantity that only have magnitude.
• For example, distance, when you measure the side of a triangle with a ruler, do you ever put negative? I don't think you will. No matter how the side started from, left to right or right to left, you will still put positive values.
• Time, is there such things as negative time or travel back time? So far, no. So 'time' is a Scalar quantity.
• Mass, if there is nothing,0 kg of mass, if there is something, T kg of mass. Then what is negative mass, do not give me craps such as ghost, supernatural phenomenon, or antiparticle. It is not in your syllabus. So, mass is a scalar.
• Energy(Joule/J), it is either you have energy or you don't have energy. There is no such thing as negative energy. Think about it, in RPG games such as final fantasy, when you have no energy, you die. Negative energy?? Is there anything beyond death??
• Temperature(Kelvin/K), the most trickiest of all. Many of you will think that temperature have negative value like -137 degrees or carbon dioxide turns into solid at -40 degree celcius. But have you guys realize, have you ever seen -1000 degree celcius? No. Why? Simple. Temperature in celcius has a minimum of -273 dC only, which is 0 Kelvin(the actual SI unit for temperature). In 0 Kelvin(absolute temperature), the particle of the substance has no energy in it(0 Joule) at all. Since there is no negative energy, there is no negative Kelvin.

There are many more scalar quantity, these are the most common.

VECTOR(means direction and amount.)

• One particular day, you were stuck with an awful stomachache. Do you ever ask "How far is the toilet?"? There correct question will be "Where is the toilet?". I am sure the answer of the question will be " It is few meters in front.". 'Few meters' is the distance, 'in front' is the direction. So the definition of vector quantity is quantity with magnitude and direction.
• Example of vector is displacement. It is the shortest distance between two location. When you ride an aeroplane, do planes follow roads? No. They follow bearing, which is the direction of where the location is.
• Force, momentum, velocity(speed with direction), and acceleration are also vector. These are new terms to you, but i'm sure you will understands why they are vector quantities, not scalar. So, i won't explain like what i explained on scalar. For now, just memorize them.

Here is a tip, all base quantities are scalar quantities.

Measuring instruments.

• 
  
  meter rule(it is spelled as rule, it is not a typo)
  
  
  
• 
  
  measuring tapes
  
  
  
• 
  
  vernier calipers
  
  
  
• micrometer screw gauge
  

ERROR

Systemic(repeating error)

• It can be due to wrong calibration of the measuring instruments. For example, a meter ruler may look fine, but actually it is wrong as its interval of 1cm is not accurately adjusted.
• Zero error. For example, a vernier calipers when completely close, do not shows a zero. The make the measurement with the vernier calipers either slightly more than the actual value or less.

Random(wrong without you notice.)

• Parallax error because of the position of your eye is wrong, you read the value wrongly.
• Environment factor such as gravity, friction, air resistance,pressure magnetic field, ambient radiation.

How to reduce error?

• Use appropriate instrument. eg. When measuring a diameter, it is better to us a vernier calipers than a meter ruler. When, measuring height of a man, it is better to measure with a meter ruler that a vernier calipers.
• Repeat the experiment many times and deduce the mean(average) value for it.
• Reduce parallax error. eg. Use the mirror in the volt meter to identify parallax error.

ACCURACY-the ability to measure something nearest to the actual value.





















CONSISTENCY-the ability to aquire the same value many times, not necessary that they are accurate.



















SENSITIVITY- the ability to detect small changes. In other words, the smaller the scale interval of the instrument, the more accurate the reading. For example, an electronic balance can is more sensitive than a triple beam balance because of the smallest scale for electronic balance is 0.01gram wheares triple beam balance can only measure up to 0.5gram accurately


PREFIXES

Have you ever read the word micrometer(um), centimeter(cm), megatonne(Mt), gigaherzs(GHz), terrabytes(Tb)? These words were added with prefixes. Prefixes make spelling for scientist more easier. Rather than spelling 512 millions bytes, they can spell as Megabytes, or even shorter, Mb. Another reason is that it makes writting down 'unit' such as cm, GPa, TN and many more in a very simple manner.The below prefixes will be needed in any field of science. But do not worry about memorizing them, you will get them eventually.

pico/p (10^-12
nano/n (10^-9)
micro/u (10^-6)
milli/m (10^-3)
centi/c (10^-2)
deci/d (10^-1)
kilo/k (10^3)
mega/M (10^6)
giga/G (10^9)
terra/T (10^12)



MICROMETER SCREW GAUGE

You are require to know every part of the MSG. Since the picture is not that clear, I will spell out the parts for you. Anvil, Frame, Spindle, Sleeve, Thimble and Ratchet. The scale on the sleeve is the main scale, wheares the scale on the thimble is called the thimble scale. Accuracy of MSG is up to 0.01mm. The function of Ratchet will always be asked. It is to prevent overturn of the thimble that might cause the thickness to deform.

HOW TO USE? I recomend you to watch at youtube because it is difficult to explain with words. Same goes for vernier calipers.



VERNIER CALIPERS