Frame of reference is a system for specifying the precise location of objects in space and time.
A simple expirement can show the need of a refrence frame :
We can choose a student in our classroom . Let’s say student E, as you can see in the given classroom figure. We want to answer to a simple question: «where is E sitting ?».
A classroom figure.
We want to answer the question but we can’t measure without a starting point. We can choose point A but we can also choose points B or C or even D.The choosen point (A or B or C or even D) will be our refrence frame . We can not conduct any measure without a refrence frame .
We can measure the distance AE or BE or CE or even DE. We can see that when we choose another point as a refrence frame, the distance of E is changing.
If we want to measure changes in position, we must chose a frame of refrence. The selected refrence frame must be fixed throught our measures.
Physics is a science that studies changes, a body that stands still throughout the course of our study has no interest.
Kinematics is the branch of physics that describes motion.
We often choose the x axis as the line along which the motion takes place. Then the position of an object at any moment is given by its x coordinate.
We can also choose the y axis when a body is falling from a roof of a building.
Distance is the length of the path taken to move from one position to another, regardless of direction.
A cute mouse is moving in a tube from – 2 m to + 5 m. Determine the total distance that mouse traveled.
The mouse traveled d = 2 + 5 = + 7 m .
Note that – 2 is +2 bacause distance is the lengh a positive number.
The lenght unit is 1 meter (m), a base unit.
We also use:
1 kilometer (km) = 103 m.
1 centimeter (cm) = 10-2 m.
1 millimeter (mm) = 10-3 m.
1 micrometer (μm) = 10-6 m.
1 nanometer (nm) = 10-9 m.
English and Americans use
1 inch (in) = 2.54 cm , where 2.54 is a conversion factor.