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
and that's the end of chapet 1!:D next up, KINEMATICS!
SOME DEFINATIONS
Displacement the distance measured along a straight line in a stated direction
Speed is the distance travelled per unit time
Instantaneous speed is the speed of an object at any instant
Velocity is the distance travelled per unit time in a stated
direction
Acceleration is the rate of change of velocity
note: rate of change CAN NEVER GO WITH per unit time. (choose 1 or the other. not both, not none either)
Free fall (with air resistance:))
something important to know first:
WHEN VELOCTY INCREASES, AIR RESISTANCE INCREASES.
means when there's acceleration, air resistance will increase.
ok, so when something is being dropped, at the very moment it is let go of, there is no air resistance acting against it. It will accelerate at 10ms-2. However, as it accelerates, speed increase, air resistance acting against it will also increase. Recall: resultant force is dependant on both the forces, the weight acting downwards and the air resistance acting upwards. when there is acceleration, there is a resutant force. no acceleration, resultant force=0) so, as the air resistant increase, the resultant force will decrease becasue the force pulling it upwards is increasing. As the resultant force decrease, acceleration will decrease too. (F=ma, F increase, m remain constant, a will increase). So, the air resistant will keep on increasing, acceleration keep decreasing (but take note, there is still increase of speed, just decreasing increase in speed) UNTIL a point when acceleration drop to ZERO. when acceleration is 0, F=ma, F=m(0) At this point, air resistance also stop increasing, as it has balanced out the mass of the object which is acting downwards. all objects in motion continues remaining in motion unless another force act on it, so the object will just keep moving at that same constant speed. this point of time, hte object has TERMINAL VELOCITY becasue it's the highest velocity it can go up to already, until if the person opens a parachute. when a parachute is opened, the big surface area of the parachute will cause the air resistance to suddenly increase alot, causing the resultant force to act upwards. BUT, the object will not move up-common sense- because it was moving downwards at a constant speed. the upwards acting resultant force just causes the object to decelerate, becasue let's say, we assign downwards as positive, upwards as negative. when resultant force is upwards, it's negative right? so F=ma, F is negtive, acceleration is negative, means there is decelaration. as the object decelerates, air resistance decreases, until the forces are balanced again, and the object will have terminal velocity again, just a much lower one.
ok i think all of that was just a totally huge mess, but dun worry, i saw an animation that sure makes it better!! http://www.darvill.clara.net/enforcemot/para1.htm
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