Term 1 Week 6

Monday
In the previous week, we learnt about the different units of measurement for physical quantities. This week, we learnt about the prefixes for them, which determine the magnitude of the unit. For example, the prefix for kg, kilogram, is kilo. We also learnt what these units stand for. For example, g, gram, on its own, has no prefix. However, 1kg is equivalent to 1000g, so the prefix kilo stands for 10 to the power of 3, a thousand, or in short, 10^3. We learnt more prefixes such as mega (M), giga (G), tera (T), which are 10^6, 10^9, and 10^12 respectively. As for the prefixes which make a unit smaller than the unit without a prefix, they are deci (d), centi (c), milli (m, not capitalised), micro (µ), nano (n), and pico (p). These are 10^-1, 10^-2, 10^-3, 10^-6, 10^-9 and 10^-12 respectively. As you may have noticed, these units are all powers of ten, which makes conversion between them much easier than if otherwise.

We also learnt conversion between units with different prefixes.

For example, 
497µm 
= (497*10^-6)m
= 0.000497m

74m^2
= (74*10^2*110^2)cm^2
= 740000cm^2

Wednesday
Before we started off the lab lesson, we learnt about significant figures. As we all know, numbers have digits, and the number of significant figures are based on these digits. So about how to count the significant figures...

1) Every non-zero digit should be counted as one significant figure. (e.g. 72136 (5 s.f.))

2) All final zeroes after the decimal point are significant. (e.g 0.1000000 (7 s.f.))

3) The zeroes in between two significant figures are counted as significant figures (e.g 50006 (5 s.f.))

4) The zeroes which do not have a significant figure to their left are not counted as significant figures (e.g. 0.000078 (2 s.f.))

5) For whole numbers, the final zeroes may or may not be significant.

We also learnt about how to do calculations for significant figures.

For addition,
The final value has the same number of decimal places (d.p.) as the least precise measurement.
e.g.
31.5 (1 d.p) + 42.67 (2 d.p. + 53.001 (3 d.p.) = 127.2 (1 d.p)

For multiplication and division,
The final value has the same number of significant figures (s.f.) as the number with the least number of significant figures.
e.g.
46.7 (3 s.f.) * 31.78 (4 s.f.) = 1480 (3 s.f.)
56.8 (3 s.f.) / 12.745 (5 s.f.) = 4.46 (3 s.f.)

For average,
The final value has the same number of decimal places (d.p.) as the least precise measurement.
e.g.
(31.1 (1 d.p.) + 42.76 ( 2 d.p.) + 20.172 (3 d.p.)) / 3 = 31.3 (1 d.p.)

For a constant (e.g. area of triangle = 1/2 * base * height, 1/2 is the constant),
The number of decimal places (d.p.) of the constant is not considered in a calculation.
e.g. 
Average = (x + y + z) / 3
(31.2 (1 d.p.) + 45.878 (3 d.p.) + 37.65 (2 d.p.)) / 3 = 38.2 (1 d.p.)

After learning about significant figures, we moved on to the experiment. The experiment was about timing the oscillations of a pendulum (made by a ball tied to a string tied to a retort stand). Basically, we let the pendulum swing for one minute and we count the number of oscillations of the pendulum and after a minute, we divide one minute by the number of oscillations made by the pendulum, to find the period, which was the time taken for the pendulum to make one oscillation. Then, we had to change the length of the string to observe the differences in the number of oscillations made per minute.

However, our teacher told us to take note of a few things.

Firstly, we had to make sure that the angle we let the pendulum go from could not be too big (around 10 degrees was preferable), or the pendulum could be extremely unstable when swinging.

Secondly, we had to watch the pendulum swinging from the front, as an oscillation is counted only when the pendulum passes the fudicial line, or the centre. From the side, we could not see whe the pendulum passes the fudicial line very well, since the centre is more easily observable fro the front.

Lastly, we had to wait for the pendulum to stabilise for a while after we let it go. We had to wait for the pendulum to make a few swings, then start the stopwatch when it crosses the fudicial line after a few swings.

So from this experiment we basically learnt the skill for measuring pendulum periods and the result of the experiment was that the longer the string was, the fewer oscillations the pendulum made in a minute.

Home-Based Learning Day
For this day (I forgot which), we were to stay at home and use the computer for, well, home-based learning. We had to log on to the iVLE portal (a portal we use for home-based learning and for some other things I do not know how to explain) and watch some videos. I would prefer going to school but well, I can't help it.

So we learnt about mass, weight, and density. 

Firstly, mass is the amount of substance in an object, as we have already learnt in primary school. So, nothing much about mass I have to say. 

Weight is measured by taking the mass of an object (in kg) and multiplying it by the acceleration due to gravity (approximately 10N/kg on Earth) so for example, the weight of a 10kg object on Earth is (10kg * 10N/kg)N = 100N. 

Density is basically, how packed the substances in an object are.

A gravitational field is an area in which an object experiences a force due to gravitational attraction.

However, some people confuse mass with weight when this is not the case. Weight is determined by the gravitational attraction in an area whereas mass is constant regardless of gravitation attraction.