SSC CGL - Detailed Guide 2025
Self-Paced Course
Motion and Force
Reference: Lucent GK, NCERT Class 6–12
Speed, Velocity, Acceleration
Speed
- Scalar quantity: only magnitude, no direction
Speed = Distance / Time
- SI Unit: m/s
- Uniform Speed: Equal distances in equal time
- Variable Speed: Unequal distances in equal time
Velocity
- Vector quantity: has both magnitude & direction
Velocity = Displacement / Time
- SI Unit: m/s
- Can be positive, negative, or zero
- Uniform Velocity: Equal displacement in equal time
- Variable Velocity: Changing speed or direction or both
Acceleration
- Rate of change of velocity
Acceleration (a) = (Final velocity − Initial velocity) / Time
- SI Unit: m/s²
- Positive Acceleration → Speeding up
- Negative Acceleration (Retardation) → Slowing down
Newton’s Laws of Motion
| Law | Statement | Explanation | Example |
|---|---|---|---|
| First Law (Law of Inertia) | A body remains at rest or in uniform motion unless acted upon by an external force | Object won’t change motion on its own | A book on a table stays still until pushed |
| Second Law | Force = Mass × Acceleration (F = ma) | Greater mass → more force needed to accelerate | Kicking a football vs. a stone |
| Third Law | For every action, there is an equal and opposite reaction | Forces act in pairs | Gun recoil when fired |
Inertia is directly proportional to mass.
Friction and Circular Motion
Friction
- Force that opposes motion between two surfaces in contact
- Acts opposite to direction of motion
-
Types:
- 1. Static Friction – Before motion starts
- 2. Kinetic Friction – While moving
- 3. Rolling Friction – Least of all (used in wheels)
- Friction is necessary (walking, driving), but also causes wear and tear.
| Way to Reduce Friction | Examples |
|---|---|
| Lubrication | Oil in machines |
| Streamlining | Aircraft, cars |
| Ball bearings | Machine wheels |
Circular Motion
- Motion of an object along a circular path
- Always accelerated due to changing direction
| Type | Description | Example |
|---|---|---|
| Uniform Circular Motion | Constant speed, but direction changes | Earth revolving around Sun |
| Centripetal Force | Force acting toward the center of the circle | String in conical pendulum |
| Centrifugal Force | Pseudo force felt outward (in rotating frame) | Feeling pushed outward in a car taking turn |
Centripetal force is real and required for circular motion.
Centrifugal force is not real in inertial frames (it’s fictitious).
Developed By Roopasree Challa
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