Overview
This lecture summarizes key mechanics concepts for Edexcel International A Level Physics, focusing on motion, forces, vectors, energy, and their related equations.
Motion Graphs
- Displacement-time graphs show position (s) against time (t); the slope gives velocity.
- A flat section means the object is stationary; a positive/negative slope indicates positive/negative velocity.
- Velocity-time graphs plot velocity (v) against time (t); the slope gives acceleration.
- Constant gradient = constant acceleration; curved lines mean changing acceleration.
- Area under a velocity-time graph equals displacement.
- Acceleration-time graphs display changes in acceleration over time, useful for non-constant acceleration.
Equations of Motion (SUVAT)
- SUVAT equations describe motion under constant acceleration with variables: s (displacement), u (initial velocity), v (final velocity), a (acceleration), t (time).
- Write “SUVAT” vertically when solving problems; identify known and unknown quantities.
- Each equation omits one variable; knowing three lets you solve for the others.
Vectors and Scalars
- Scalars have magnitude only (e.g., distance, speed); vectors have both magnitude and direction (e.g., displacement, velocity).
- Use arrows to represent vectors; length = magnitude, direction = direction.
- Vectors can be resolved into horizontal (vx = v cosθ) and vertical (vy = v sinθ) components.
- Add vectors by scale drawing or calculation (Pythagoras and trigonometry if at 90°).
Projectile Motion
- Treat horizontal and vertical motions independently when air resistance is negligible.
- Horizontal velocity stays constant; vertical velocity changes due to gravity.
- Use SUVAT for both directions; time is the same for both.
- Define positive and negative directions as needed.
Forces and Newton’s Laws
- Free-body diagrams show all forces on an object; sum gives resultant (net) force.
- Newton’s First Law: balanced forces mean no acceleration (constant velocity).
- Newton’s Second Law: resultant force = mass × acceleration (F = ma).
- Newton’s Third Law: forces between two objects are equal and opposite.
- Weight = mass Ă— gravitational field strength (g = 9.81 N/kg on Earth).
Momentum and Collisions
- Momentum (p) = mass Ă— velocity; it is a vector and conserved in closed systems.
- Total momentum before a collision equals total momentum after.
- Newton’s Second Law can be written as force = rate of change of momentum.
Moments and Equilibrium
- Moment = force Ă— perpendicular distance from pivot; units: Nm.
- Center of gravity is the point where an object’s weight acts.
- Equilibrium: resultant force and resultant moment are zero (object is balanced).
Work, Energy, Power, and Efficiency
- Kinetic energy = ½ × mass × velocity².
- Gravitational potential energy = mass Ă— g Ă— height.
- Work done = force Ă— distance moved in the direction of force.
- Power = energy transferred or work done per unit time; units: Watts (W).
- Efficiency = useful energy (or power) output Ă· total input; express as a ratio or percentage.
Key Terms & Definitions
- Displacement (s) — Distance moved in a specific direction (vector).
- Velocity (v) — Rate of change of displacement (vector).
- Acceleration (a) — Rate of change of velocity (vector).
- Scalar — Quantity with magnitude only.
- Vector — Quantity with magnitude and direction.
- Momentum (p) — Mass × velocity (vector).
- Moment — Turning effect of a force about a pivot.
- Kinetic energy — Energy of a moving object.
- Gravitational potential energy — Energy stored due to height in a gravitational field.
- Work done — Energy transferred by a force moving an object.
- Power — Rate of doing work or transferring energy.
- Efficiency — Ratio of useful output to total input.
Action Items / Next Steps
- Practice drawing and interpreting motion graphs.
- Memorize the four SUVAT equations and understand their variables.
- Practice resolving vectors and using trigonometry in vector problems.
- Review Newton’s Laws and apply them to various scenarios.
- Complete any assigned core practicals (e.g., measuring acceleration due to gravity).