Kinematics is the branch of physics that describes the motion of objects without considering the forces that cause the motion. It focuses on displacement, velocity, acceleration, and time in one, two, or three dimensions. For the IJSO, we only consider one or two dimensional kinematics.
There are 4 equations in kinematics:
\( v = u + at \)
\( s = ut + \frac{1}{2}at^2 \)
\( v^2 = u^2 + 2as \)
\( v_{avg} = \frac{v + u}{2} \)
Where:
\( u \): initial velocity
\( v \): final velocity
\( a \): acceleration
\( s \): displacement
\( t \): time
Let’s see some examples and you will understand how kinematics work
A car starts from rest and accelerates at \( 2 \, \text{ms}^{-2} \) for 5 seconds. Find the final velocity of the car and the distance traveled.
Known: \( a = 2\,\text{ms}^{-2}, t = 5\,s, u = 0\,\text{ms}^{-1} \)
\( v = u + at = 0 + 2 \times 5 = 10\,\text{ms}^{-1} \)
\( s = ut + \frac{1}{2}at^2 = 0 + \frac{1}{2} \times 2 \times 25 = 25\,\text{m} \)
A ball is thrown vertically upward with an initial velocity of \( 30\,\text{ms}^{-1} \).
\( a = -10\,\text{ms}^{-2}, u = 30\,\text{ms}^{-1}, v = 0 \)
A cyclist moving at 5 m/s starts accelerating at 1 m/s² for 10 seconds, then decelerates at 0.5 m/s² until coming to rest. Find the total distance and total time.