This series of lessons is designed to help you learn, or review, the fundamentals of physics. We start off with the very basics: speed, time, distance, etc.
Physics: the study of matter, motion, space and time
Sounds really cool, doesn’t it? And it is. But before we start off, we need to begin with a few basic definitions:
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Distance (d):
The amount of space between 2 points. Measured in metres (m).
Time (t):
The measurement of duration of events. Measured in seconds (s), minutes (min), hours (h), etc.
These basic 2 definitions are required to study the very basics of classical mechanics in physics- motion. Motion has to do with rate. We’ll now introduce another important concept:
Speed (v):
The rate of change of distance over time, measured in metres per second (m/s),kilometres per hour (km/h), etc.
Hold on a second (bad pun intended)
Yes, this is the basic definition of speed. It brings us a nice and easy formula to memorize:
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So, for example, let’s say I’m moving 4 metres in 2 seconds. What’s my speed? Easy:
That’s it.
The only disadvantage of using this type of measurement is that while we know the magnitude of the motion, we don’t know anything about the direction.
Introducing: Vectors
Vectors are measurements that include both magnitude and direction.
For example, a scalar (non-vector) is 5 km. A vector is 5 km North. We can use arrow to donate vectors, scaling them down, as follows:
Position:
Indicates a distance from a point of reference.
Displacement (d):
A vector that indicates the position of a point relative to another point of reference.
This can be confusing, but an example will help clear things up. Say, for example, I’m 20 metres north of my home, I’m at position 20m N relative to my home. The displacement between me and my home is 20m N.
Velocity (v):
the rate of change of displacement over time.
Again, holds.
Now we’ve introduced the important basic concepts of motion
Next time, we’ll see how vectors are added and manipulated.
Thanks for reading this Welcome to Physics Lesson!
Nice lesson, thanks.
I seem to recall that there is a formula for determining someone’s change in weight (or weight equivalent) when they travel at a certain speed – e.g. when an unbelted driver who weighs 70 kg comes to a sudden stop from 100 km/hr they’re weight is…......?
Nice lesson, thanks.
I seem to recall that there is a formula for determining someone’s change in weight (or weight equivalent) when they travel at a certain speed – e.g. when an unbelted driver who weighs 70 kg comes to a sudden stop from 100 km/hr they’re weight is…......?
The regular concept of weight is really just the force of gravity that acts on a person with a certain mass. Then a person with mass 70 kg will have a weight of 70 * 9.8= 686 N. The formula would be FW (weight)=mg, where g is gravity, 9.8, and m is your mass.
In your example, since you’re moving forward and not up/down, there should be no effect on your weight, since gravity works only downwards. However, if you’re looking for the net force, which is a sort of weight equivalent, that acts on you in this situation you describe, all you have to do is apply the general formula F=am, where a would be your acceleration. Look at Phsyics VI for more information.
I hope this answers your comment.
Good session for startup…but i would prefer to have the definition of velocity as you mentioned as rate of change to be mathematically depicted as v = d(x)/dt ,where x is the distance..
Good session for startup…but i would prefer to have the definition of velocity as you mentioned as rate of change to be mathematically depicted as v = d(x)/dt ,where x is the distance..
I absolutely agree that this definition is more proper. However, I rather refrain from using it, since this level of physics is only very basic, so getting into calculus terms may cause some confusion for people who haven’t been introduced to things like the dx/dy notation, derivatives, etc.
But yes, velocity is defined as the derivative of distance over time (dx/dt, or dd/dt if you use d for distance, although that’s a bit confusing), and then acceleration is the derivative of velocity with respect to time, which is also the second derivative of acceleration.
It would probably be a good idea to emphasize that in my lesson, I’m using d and t for the change in distance and time, respectively, not just any random values.
Thanks for pointing this out!
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