This guide covers the fundamental concepts of how things move, a key area in the Physics section of your exam.

1. Short Notes: Core Concepts

A. Scalars vs. Vectors This is a crucial difference you must know!

• Scalar: A quantity with magnitude (size) only. Examples: distance, speed, time, mass.

• Vector: A quantity with both magnitude and direction. Examples: displacement, velocity, acceleration, force.

B. Key Quantities & Formulas

• Deceleration: This is just a negative acceleration, meaning the object is slowing down.

• Motion under Gravity (g): When an object falls freely, it accelerates downwards due to gravity. This is called gravitational acceleration (g). Its value is approximately 9.8 m/s² (often simplified to 10 m/s² in exams).

C. Graphs of Motion: The Visual Story Graphs are a very common way to test your understanding.

1. Displacement-Time (s-t) Graphs:

• What it shows: Where an object is at any given time.

• Key Info: The gradient (slope) of the line tells you the velocity.

  • Horizontal line: Gradient is zero -> Object is at rest (not moving).

  • Straight, sloping line: Constant gradient -> Constant velocity.

  • Curved line: Changing gradient -> Acceleration.

2. Velocity-Time (v-t) Graphs:

• What it shows: How fast an object is moving at any given time.

• Key Info:

  • The gradient (slope) of the line tells you the acceleration.

  • The area under the graph tells you the displacement.

  • Horizontal line: Gradient is zero -> Constant velocity (zero acceleration).

  • Straight, sloping line (upwards): Constant positive gradient -> Constant acceleration.

  • Straight, sloping line (downwards): Constant negative gradient -> Constant deceleration.

2. Tips & Tricks for the Exam

• Vector Direction is Key: For displacement and velocity, direction matters. If an object moves 10m east and then 4m west, its distance is 14m, but its displacement is 6m east. A negative velocity or acceleration simply means it's happening in the opposite direction.

• Graph Summary:

  • s-t graph: Gradient = Velocity

  • v-t graph: Gradient = Acceleration | Area = Displacement

• Units Matter! Always write the correct units (m, m/s, m/s²). It can cost you marks if you forget. Ensure all your calculations use standard units (convert km to m, minutes to seconds, etc.).

• "Starts from rest" means initial velocity (u) = 0.

• "Comes to rest" means final velocity (v) = 0.

3. Important Points & Common Exam Questions

• Distance vs. Displacement: This is a classic. A common question involves an athlete running around a circular track. After one full lap, the distance is the circumference of the track, but the displacement is zero because they are back where they started.

• Interpreting v-t Graphs: This is the most important skill for this topic. You will almost certainly be given a v-t graph (often a trapezium shape) and asked to:

  • Describe the motion: Break it down into sections (e.g., "From 0s to 6s, the object accelerates uniformly...").

  • Calculate the acceleration/deceleration: Find the gradient of a sloping section.

  • Calculate the total displacement: Find the total area under the graph. Remember the formulas for the area of a rectangle (l x w), a triangle (½ x base x height), and a trapezium (½ x (a+b) x h).

• Free Fall Problems:

  • An object is dropped from a tower. What is its velocity after 3 seconds? (Assume g = 10 m/s²)

    • Its velocity increases by 10 m/s every second. So, after 3s, velocity = 3 x 10 = 30 m/s.

  • What is the distance it has fallen?

    • This is the area under the v-t graph for this motion. Area = ½ x base x height = ½ x 3s x 30m/s = 45m.