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Before we Begin
Kinematics is the study of an object's motion, from figuring out how far a marble has rolled; to how fast a rocket needs to go to escape Earth's orbit; to how high an arrow should be aimed to get a bulls-eye.
Most examples of things moving in real life have so many variables affecting their motion, such as friction or air resistance. To create a formula to account for these is quite complex, so in Year 12 Physics it is omitted. Instead we automatically assume there is no friction, air resistance, or whatever else we state in our answer to a question.
Before you look at the main pages, be sure you know about the following elements.
Purple Tooltips
Throughout this web site you'll encounter purple tooltips like the one below. If you move your mouse over them, you'll see some extra information about the word or words in purpleA colour which is a mixture of blue and red..
Flash
Some content on this website was created with Macromedia Flash MX, and may require Flash Player in order to view. To learn about Flash Player, Click Here.
Significant Figures
Whenever we tackle a physics question, we need to ensure that our answer is accurate.
Quiz time: If we measure how far a tennis ball has been rolled, which measurement would have been from using a standard meter ruler?
aRuler A is able to measure tenths of a millimeter? That sounds a little farfetched, because otherwise the ruler would be full of little lines telling you the length of 0·1mm, then 0·2mm, then 0·3mm...) ·1281m
bRuler B is able to measure in tenths of a centimeter, that sounds a bit reasonable, because tenths of a centimeter are exactly the same as millimeters (which you'll find out in the next section).) 1·281m
cRuler C can only measure in divisions of ten centimeters. This is quite useless for small measurements, because you can only get measurements of 10cm, then 20cm, then 30cm.) 128·1mBelieve it or not, the answer is B; although if you picked A or C you may need to think about getting a less high-tech meter ruler.
Significant figures tell us how accurate a measurement is, and saves us writing loads of decimal points at the same time.
Say we had a measurement of 26cm. It could be any measurement between 25·5 and 26·5cm, but it has been rounded to stop us from writing too many digits. It has two significant figures, because it has 2 non-zero digits.
If the measurement was 30cm, it would have one significant figure. 0.0005km also has one significant figure.
There is a slight exception to this rule, however. If our measurement is 0.00307 or 307000km, it has three significant figures. Why? because the zero is part of the main number that was rounded, i.e. the previous number could have been 306938, which rounds to 307000.
Whenever we write an answer we tend to look at all the numbers we put in, and find the least amount of significant figures in any number, and use that in our answer. For example, if we put the measurements of 57cm, 28s and 312ms-1 into a formula, we would give the answer to 2 significant figures.
You will notice that on our site our answers will have (# s.f.) after them (the # will be replaced with a number).
However, the less significant figures there are, the less accurate the number could be.
This brings up an important point: if someone told you they threw a ball 1000cm, chances are they didn't throw it exactly 1000cm (if they did, congratulate them for me). They could have thrown the ball anywhere between 1500cm and 500cm. But they actually threw the ball 997·6cm, and they only wanted it to have two significant figures, not one.
It's an easy solution. Just write this.
1000cm (2 s.f.)
Which says the first zero is accurate, but the other two are placeholders.
SI Units
SI Units are units used for telling one measurement apart from another. These are important in physics because we use a lot of different types of measurements.
Quiz time (again): A person just went for a walk, and gave you the measurement 17. Does this mean:
a) They ran for 17 seconds?
b) They ran 17 kilometers?
c) They tripped over 17 times?
d) 17 is their favourite number?Note: Depending on the runner the answers could be different. For instance, if the runner was me, answers A, C and D would probably apply; but that's not the point of this question.
The point is the importance of SI Units, they tell us what the measurement is for.
To use a SI Unit, simply place it after the number in question.
Below is a table of the SI Units you will encounter in this website.
Name Symbol Measured in... Unit Distance/Displacement d meters m Time t seconds s Speed/Velocity v meters per second ms-1 Acceleration a meters per second squared ms-2 Some SI Units (such as distance) usually have metric prefixes in front of them, to indicate the scale of a measurement. In other words...
Below we have two identical measurements. Would you rather write:
a) 1000000mDon't worry, we wont be using measurements as large as these on this website. (one million meters)
or
b) 1Mm (1 mega meter)?B is the sensible answer, in case you were wondering.
Below is a table of the most common metric prefixes.
Values in blue are used in other parts of Year 12 Physics.
Values in green are not used extensively in Year 12 Physics.
Name Symbol Multiplier giga- G 1000000000 billion mega- M 1000000 million kilo- K 1000 thousand hecto- H 100 hundred deca- da 10 ten deci- d 0.1 tenth centi- c 0.01 hundredth milli- m 0.001 thousandth micro- µ 0.000001 millionth nano- n 0.000000001 billionth These metric prefixes prevent us from writing too many zeroes. To use a prefix, simply place it in front of the SI unit like so:
1000m = 1km
0.002ms-1 = 2mms-1Time measurements do not use the metric prefix system, but general knowledge should tell you that there are...
60 seconds in a minute
60 minutes in a hour
3600 seconds in an hourMathematical Prerequisites
Now that's a fancy word! What we are just quickly going to mention is that to do some of the examples in kinematics, you will need to know a bit about algebra and trigonometry. If you don't, you may need to look some formulae up, but we'll try to explain working as best as we can.
Right, that's enough writing on this page. It's time to take the...
If you know what section of kinematics you are looking for, use the button at the bottom of this page to return to the top, and select the category using the buttons on the right hand side. If you are just starting out, we recommend looking at the Displacement page.
