PHYSICS:)
CHAPTER 1--MEASUREMENTS:)
physical quantities (scalar) (e.g. cm, m, kg, degrees, all the normal units)
- numerical magnitude (number)
- unit
physical quantities (vector) (e.g. acceleration, displacement, velocity)
-numerical magnitude
-unit
-DIRECTION
Base quantities (SI units)
There are 7 like the colours of a rainbow:)
-Length (m)
-Time (s)
-Mass (kg!)
-electric current (A)
-Thermodynamic temperature (K)
-Luminous intensity (cd)--cd, like the cd u know?
-Amount of substance (mol)--mole (on your face!)
Derived quantities
-quantities derived from the base quantities? (e.g. area, volume, speed)
Prefixes
10 to the power of:
-9=nano (n)
-6=micro (the wierd m sign)
-3=milli (m)
-2=centi (c)
-1=deci (d)
3=kilo
6=Mega
9=Giga
MEASUREMENTS OF LENGTH!
-SI unit is the metre (i always thought it was meter..) symbol is m.
-some common instruments: metre rule, tape measure, vernier calipers etc
some common errors:
1. instrument error
--using an instrument with unsuitable accuracy! (e.g. using metre rule to measure thickness of paper
2. Random error
--occurs in all measurements, tehre is no fixed patterns (too random! how to predict?)
--minimise by taking a large number of readings, then averaging them (before hand, discard any ridiculous readings!)
3. Systemic error
--e.g. zero error.
--due to faulty equipments/wind
--the readings are consistently lower or higher
metre rule and tape measure
-accuracy of 0.1cm/1mm
Some precautions to take
1. Avoid parallax error (position your eye above at the same level as the markings, place the instrument at the same level too!)
2. due to wear and tear of the ends, it's better to measure from another random point along the ruler and then subtract it from final reading
Calipers
-grip the widest part of the object, then measure with metre rule
VERNIER CALIPERS!!:)
parts: main scale, sliding vernier scale, inside jaws, outside jaws, tail
precision: 0.1mm/0.01 cm
Some precautions to take when usign vernier calipers:
1. check for zero error before using and subtract it off from final reading. Take note! negative zero error is count from right to left! (10 is 0, 9 is 1 etc)
2. objects to be measured msut be gripped gently between the jaws
NEXT IS MY FAVOURITE! MICROMETER SCREW GAUGE!:)
-accuracy is 0.01mm/0.001cm
-parts: anvil, spindle (the stick like thing), main scale, thimble scale, thimble, ratchet
some precautions to take note of:
1.When spindle and anvil is closed, check for zero error. Add or subtract the error from reading to get the actual reading.
2.Do not overscrew. This can be done by turning using the ratchet until a clicking sound is heard. (but don't turn the thimble all the way first! turn until left abit then turn ratchet the rest of the way)
3.Take measurements at different locations and find the average reading.
–E.g take 3 diameter readings along entire length of thin wire, then find the average.
–There can be manufacturing errors
ok next, time!(: something that we never seem to have enough eh?
First up, you must know that to measure time, you need ot make use of something with recurrent motions at specific intervals (e.g. sun setting and rising, pendulum!)
Pendulum
-one full swing from left to right and back to right is called an oscillation. treat it like a runner going around a track. must run and come all hte way back then is one round!
-period is the time taken for an oscillation
the period is INDEPENDANT OF (not affected by):
-angle of swing (provided it's 5-10 degrees)
-mass of pendulum bob
The period is affected by:
-length of pendulum
-acceleration due to gravity
Just remember, if angle of swing higher, it won't make a difference becasue although it will mvoe faster, it has to travel longer distance. the mass don't make a difference when it's fast it will go faster, but when it's slow it will take longer to slow down too. length of pendulum is indirectly like telling the pendulum to travel a longer distance! acceleration due to gravity is basically 10ms-2 without air resistance, and will be same as long as it is in earth.
•Precautions for oscillations:
–Ensure that the angle of swing is small (5-10 degrees)
–Ensure the swing is steady before starting to time (let it swing a few times first)
–Ensure that the path of the bob is straight and not elliptical (elliptical will cause it to travel in circles! imagine you running in wierd circles in a race!)
Ticker tape timer
-basically, it will hit at regular intervals
-if the number of times it hits per second is x, each interval is 1/x seconds
-when intervals get bigger, means object is accelrating, smaller means object is decelerating.
Stopwatch
1) Analogue : accuracy up to 0.1 s
2) Digital: accuracy up to 0.01 s
–Average human reaction time: » 0.2 to 0.3s
– *** To account for human reaction time, recordings with a digital stopwatch can be corrected to one decimal place
Chapter 2- Kinematics
FREE FALL
1. objects falling without air resistant
2. at every point, they have an acceleration due to gravity of 10ms-2, downwards
3. ALL free falling objects fall at the same speed
take note: free fall only takes place when the question says "ignoring air resistance" etc
Without air resistance
1. air resistance act against the motion of the moving objects
2. air resistance INCREASE as speed of the object INCREASE
3. air resistance INCREASE as surface area of the object INCREASE
4. air resistance INCREASE as density of air INCREASE
How to describe terminal velocity important!
- Initially, the only force acting on the ball is the weight, hence the ball will accelerate at 10 ms-2
- After some time, the air resistance increases as speed increases.
- The resultant force downward is reduced and the acceleration decreases.
- Eventually, when the weight of the ball is equal to the air resistance, the resultant force becomes 0 N.
- In accordance to Fnet = ma, the acceleration will be 0ms-2 and the ball will fall with terminal velocity
one heart, one mind,one dance