Force, Motion and Work

Overview

Force, Motion and Work form the foundational mechanics unit for TET-2 Science. This topic connects everyday experiences—pushing a cart, riding a bicycle, using a lever—to fundamental physics principles. Questions typically test conceptual understanding of Newton's laws, types of friction, work-energy relationships, and mechanical advantage of simple machines.

Expect 3–5 questions from this topic, often scenario-based: calculating work done, identifying the type of friction in a situation, or determining mechanical advantage. Mastery requires both formula recall and the ability to apply concepts to real-world examples that upper primary students encounter.

The key challenge is distinguishing closely related terms (force vs pressure, speed vs velocity, work vs energy) and remembering that physics definitions often differ from everyday usage—for instance, holding a heavy bag involves no "work" in physics terms if there's no displacement.

Key Concepts

• **Force** is a push or pull that can change an object's state of rest or motion, its shape, or its direction. SI unit: Newton (N). Force is a vector quantity (has magnitude and direction).

• **Balanced vs Unbalanced Forces**: Balanced forces produce no change in motion (net force = 0). Unbalanced forces cause acceleration or deformation.

• **Friction** is the force that opposes relative motion between surfaces in contact. It depends on the nature of surfaces and the normal force, not on area of contact.

• **Types of Friction**: Static friction (prevents motion from starting) > Sliding friction > Rolling friction. Fluid friction acts in liquids and gases.

• **Newton's Laws of Motion**: First law (inertia)—objects resist change in motion. Second law—F = ma (force equals mass times acceleration). Third law—every action has an equal and opposite reaction.

• **Work** is done only when force causes displacement in its direction. W = F × d × cos θ. No displacement or perpendicular force means zero work.

• **Energy** is the capacity to do work. Forms include kinetic (motion), potential (position), heat, light, sound, and chemical energy. Energy transforms but is neither created nor destroyed (law of conservation).

• **Simple Machines** multiply force or change its direction. Six types: lever, pulley, wheel and axle, inclined plane, wedge, screw. They reduce effort but never reduce work.

Formulas / Key Facts

| Quantity | Formula | Unit | Notes | |----------|---------|------|-------| | Force | F = m × a | Newton (N) | 1 N = 1 kg·m/s² | | Weight | W = m × g | Newton | g ≈ 10 m/s² (approx) | | Work | W = F × d | Joule (J) | 1 J = 1 N·m | | Kinetic Energy | KE = ½mv² | Joule | Depends on velocity squared | | Potential Energy | PE = mgh | Joule | Height from reference level | | Power | P = W/t | Watt (W) | 1 W = 1 J/s | | Mechanical Advantage | MA = Load/Effort | No unit | Higher MA = less effort needed | | Velocity Ratio | VR = Distance moved by effort / Distance moved by load | No unit | — | | Efficiency | η = (MA/VR) × 100% | Percentage | Always < 100% in real machines |