All of AQA Mechanics and Materials - A Level Physics REVISION

Projectile Motion

Independence of Motion: In projectile motion, an object experiences two independent components of motion: vertical and horizontal. This principle allows us to analyze each component separately.

Types of Projectile Motion:

• Horizontal Projection: Objects projected horizontally follow a parabolic path due to the influence of gravity.

• Angle Projection: Objects projected at an angle ascend and descend along a parabolic trajectory.

Equations of Motion: To solve problems, it is crucial to write down the relevant equations and identify the known variables. The assumption of zero horizontal acceleration makes the initial velocity equal to the final velocity in the horizontal direction.

Vertical Motion Acceleration: Often considered as downwards due to gravity (G = 9.81 m/s²).

Forces and Drag

Real-World Conditions: In practical scenarios, air resistance and other drag forces alter the idealized motion of projectiles. This impacts the trajectory and distance travelled by the object.

Terminal Velocity: As an object accelerates downwards, the drag force increases until it balances the weight, resulting in constant terminal velocity. This occurs because the net force and acceleration become zero.

Newton's Laws of Motion

• First Law: An object remains at rest or in uniform motion unless acted upon by a resultant force.

• Second Law: The resultant force acting on an object is proportional to the rate of change of momentum (F = ΔMV/ΔT).

• Third Law: For every action, there is an equal and opposite reaction force between two objects (A affects B equally).

Acceleration Relationship: F = MA indicates acceleration is directly proportional to force and inversely proportional to mass.

Momentum

Definition: Momentum (p) is defined as mass (m) multiplied by velocity (v) (p = mv).

Conservation of Momentum: Momentum before an event (collision or explosion) equals momentum after the event, maintaining the principle of conservation in closed systems.

Collisions

Elastic vs. Inelastic Collisions:

• Elastic: Both momentum and kinetic energy are conserved.

• Inelastic: Momentum is conserved, but kinetic energy is not; some energy is transformed into other forms (thermal, sound).

Impulse and Forces

Impulse: The product of force and time equals the change in momentum (Impulse = F × Δt = Δp). This is critical when analyzing collisions.

Force-Time Graphs: The area under a force-time graph represents the impulse provided to an object.

Work, Energy, and Power

Work-Energy Principle: Work done (W = F × s) transfers energy between stores; the direction of force and distance moved must be considered (W = F cos(θ) × s).

Graphical Work: The area under a force vs displacement graph equates to the work done.

Power: Defined as the rate of doing work or transferring energy (P = W/t or P = F × v).

Efficiency: Efficiency is the ratio of useful output energy or power to the total input energy or power, usually expressed as a percentage.

Energy Stores and Conservation

Gravitational Potential Energy: Given by the formula: GPE = mgh (mass × gravitational field strength × height).

Kinetic Energy: KE = 1/2 mv² describes energy due to motion.

Pendulum Energy Transformations: A pendulum alternates between potential and kinetic energy at various points of its cycle.