IB Physics A.1 Kinematics

Describing Motion:

• Displacement (s): The change in position with direction. It’s a vector! (Units: m)
• Velocity (v): The rate of change of displacement. Also a vector!
• Average Velocity: Total displacement / Total time.
• Instantaneous Velocity: Velocity at a specific instant (tangent to s-t graph). (Units: m/s)
• Acceleration (a): The rate of change of velocity. Yep, a vector!
• Average Acceleration: Change in velocity / Total time.
• Instantaneous Acceleration: Acceleration at a specific instant (tangent to v-t graph). (Units: m/s²)

Note: Speed is the magnitude of velocity (scalar). Distance is the total path length (scalar).

The Mighty SUVAT Equations (Constant Acceleration Only!):

Memorize these five equations. They are your workhorses for linear motion with uniform acceleration:

1. $v = u + at$
2. $s = ut + \frac{1}{2}at^2$
3. $v^2 = u^2 + 2as$
4. $s = \frac{(u+v)}{2}t$

Where:

• $s$ = displacement
• $u$ = initial velocity
• $v$ = final velocity
• $a$ = constant acceleration
• $t$ = time

Top Tip: Identify your knowns and unknowns. Pick the equation that links them! Be strict with positive and negative signs for direction.

Motion Graphs - Visualizing the Journey:

• Displacement-Time (s-t):
  • Gradient = Velocity
  • Straight line (constant gradient) = Constant velocity
  • Curve (changing gradient) = Acceleration
• Velocity-Time (v-t):
  • Gradient = Acceleration
  • Area under the graph = Displacement
  • Horizontal line = Constant velocity
  • Sloped line (constant gradient) = Constant acceleration

Projectile Motion - Launching into 2D:

• Horizontal Motion: Constant velocity ($a_x = 0$). Use $s_x = u_x t$.
• Vertical Motion: Constant acceleration due to gravity ($a_y = -g \approx -9.81 \, m/s^2$). Use SUVAT equations for the vertical components ($s_y, u_y, v_y$).
• Time is the Connector! The time of flight is the same for both horizontal and vertical motion.

Final Quick Pointers:

• Always include units!
• Distinguish clearly between scalars and vectors.
• Sketching the scenario often clarifies the problem.
• Practice a variety of questions to solidify your grasp.