There are a number of topics in the syllabus. The names of these topics are mostly familiar in everyday English - light, electricity, heat, ... But there is one topic that has a less familiar name - the topic called kinematics.

For topics like heat, electricity, light - we tend to hear these words in everyday life. Even for nuclear physics, we hear about this now and then in the news, especially when there are conflicts among powerful countries like the USA and Russia.

But what is "kinematics" ??

The contents of this topic is actually quite familiar. It is all about distance, speed, acceleration, and related stuff. Just what we see and do everyday when we walk, run, take bus, train, ... !

But of course, being a topic in physics, we have to learn to think a lot harder about these familiar actions. For example, we learn the idea of putting distance that we walk and the direction together as a single idea - called displacement.

We also learn that the meaning of the word "velocity" in physics is not just speed, but also includes direction. So we cannot just say I walked at a velocity of 10 metres per minute, which our friends would understand perfectly. In physics, we must say I walked at a velocity of 10 metres per minute to the East.

So the common everyday word gets loaded with extra meaning. This - unfortunately - is probably the reason why many students get confused when they learn physics. It does take some time and patience to get used to.

We have two related numbers like distance and time, both changing together. This is a lot more information our mind has to take in. The simple way to understand this is usually to use a graph.

A graph is basically a picture. As the saying goes - a picture says a thousand words. So rather than saying a car moves 2 metres in the first second, 3 m in the next second, 2.5 m in the third second - a graph can show all these information at one look.

Not only that. A graph can also contain hidden meanings that we have to learn to find.

A graph of velocity plotted against time appears to show just a curve that tells us the velocity of say a car at different times. But do you know that there is information hidden in this graph? The area under the curve tells us the distance that the car travels!

And that is not all. The line of the graph may go up or down. If the velocity-time graph is more steep, that means that there is bigger acceleration. And the acceleration can actually be calculated from the steepness of the graph.

So there are "hidden meanings" in different aspects of the graph. Together, they contain the information that the graph want to show.

And being a physics subject, we cannot run away from mathematics. There are a few equations we have to learn - equations that relate quantities like displacement, velocity, acceleration and time.

These equations allow us to find some of the quantities like displacement, velocity or acceleration, if we know the values of the other quantities. We can do simple things like calculating the time it takes to go to school if we know the speed and distance of a bus.

We can also do more complicated calculations like finding the speed of a bottle dropped from the 7th floor to the ground floor. The bottle would have about the same speed as a very fast car on the expressway. That is why high-rise littering - or littering from high floors - is so dangerous.

While the equations are useful, we also learn that they have some limitations when we use them to calculate movement of things in the real world. It is quite accurate when we use them to calculate the time it takes for a stone for fall to the ground. But clearly, we would get the wrong answer if we use the same equations to find the time it takes for a feather to fall.

The reason is that the air around us actually gives resistance as we move through it. We feel this if we walk through strong wind. So when a stone falls under the force of gravity, the air resistance would resist the movement of the stone. Like friction, the air exerts an upward force on the stone. But we don't normally notice this because at low speed, this resistance is a lot smaller than the weight of the stone.

But it becomes very obvious with a feather. As feather is very light, its weight might not be much larger than the air resistance. That is why the feather obviously falls a lot more slowly.

Finally for this topic, we also learn that there is something special about an object moving in a circle. If we give a knock on a small object on a slippery floor, the object would slide across the floor in a straight line. It would not go round a circle on its own.

To make it go in a circle, we actually need a force to keep push the object sideways - so that the object changes direction. Not only that, we also need the force to keep pushing sideways at the object all the time. If we let go, the object would just go straight again.

Remember that even if this object is moving at constant speed, because it keeps changing direction in a circular motion, its velocity is changing. This is perhaps one of the difficult things to understand when we learn physics. We are used to thinking that speed and velocity are the same.

This means there is acceleration when going round a circle at the same speed. So circular motion has acceleration even though the speed stays the same !

The examples above tell us something about the way things move. But why do they move in the first place? The answer is in the next blog on dynamics.

You can learn these concepts and more at Dr Hock's maths and physics tuition.