KINEMATICS
| Kinematics is a branch of physics that discusses the motion of objects without paying attention to the causes of their motion. The cause of motion that is often reviewed is force or momentum.
The movement of an object can be in the form of translation or displacement, rotation and vibration. This material discusses translation and rotation movements only. Meanwhile, vibrational motion will be discussed in the next material related to harmonic motion.
There are three physical quantities used to determine the motion of a partacle, namely:
1. Position (r), units in meters Relative position, displacement (Δr), distance traveled
2. Velocity (v), unit m / s Average (v average ) and instantaneous (v) velocity
3. Acceleration (a), unit m / s 2 average acceleration (a average ) and instantaneous (a)
TRANSLATION MOVEMENT
Examples of translational motion: chasing objects from one object to another, the car moving from city A to city B and so on.
Examples of rotational motion: the planet Mercury around the sun, electrons around the atomic nucleus, spinning helicopter blades, and others.
POSITION
An object's displacement is characterized by its position in the object. The change in position of an object is always expressed in the time parameter. For example, a bus trip from Bandung to Jakarta. Therefore the object's position is a function of time.
Position: X = f (t)
The image below shows the coordinates of the bus position at a certain time. From the picture obtained at 07:00 the position of the bus is still in Bandung. One hour later his position was in Ciranjang. 09:00 am in the city of Cianjur. And at 10:00 am in Jakarta.
Examples of the position versus time function:
X(t) = 2t2 + 2t -1
X (t) = ln (t 2 ) for t ≥ 1
The equation for position as a function of time is in a one-dimensional framework, because objects move only in the X coordinate direction.
For a two-dimensional or three-dimensional frame the position must be expressed in vector form in terms of the direction of the X coordinate axis, the component of the Y coordinate axis, and the component of the Z coordinate axis.
2D AND 3D MOVEMENT
Two dimensions:
R(t) = X(t) i + Y(t) j
Example:
R(t) = t i + (t + 1)j
R(t) = r(cos ɷt i + sin ɷt j)
Three dimension :
R(t) = X(t) i + Y(t) j + Z(t) k
Example:
R(t) = t i + (t + 1)j – k
R(t) = r(cos ɷt i + sin ɷt j) + k
SPEED
Another measure in translational motion which expresses the change in position with respect to time is velocity. Generally, position is expressed in vector form (except for one-dimensional motion), so velocity is also a vector quantity. The velocity of an object is equal to the derivative of its position with respect to time.
Velocity: v (t) = dr (t) / s
Example:
Posisi: r (t) = t i + (t + 1) 2 j - k
Kecepatan : v(t) = i + (t - 1)j
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