Overview
This lecture covers Newton's Second Law of Motion, the formula for calculating force, and applies these concepts to road transport and the idea of inertial mass.
Newton’s Second Law of Motion
- Newton’s Second Law states acceleration is proportional to the resultant force and inversely proportional to the object's mass.
- If two equal masses experience different forces, the one with the greater force has greater acceleration.
- For equal forces, the object with less mass accelerates more.
Calculating Force, Mass, and Acceleration
- The equation: Force (N) = Mass (kg) × Acceleration (m/s²) must be memorized for exams.
- Example: A 5 kg object with 4 m/s² acceleration requires 20 N of force.
- Example: A 0.5 kg object with a 50 N force will accelerate at 100 m/s².
Estimating Road Transport Values
- Cars typically travel at 13 m/s on main roads and 30 m/s on motorways.
- Acceleration from a main road to motorway averages about 2 m/s².
- A typical family car needs about 2,000 N of force to reach motorway speed.
Inertia and Inertial Mass (Higher Tier)
- Inertia is an object’s tendency to maintain its motion or rest unless acted on by a resultant force.
- Inertial mass measures how much force is needed to change an object’s velocity.
- Inertial mass is defined as force divided by acceleration.
- Objects with greater inertial mass need more force for the same acceleration.
Key Terms & Definitions
- Resultant Force — The overall force acting on an object after all forces are combined.
- Acceleration — The rate of change of velocity, measured in m/s².
- Inertia — The resistance of an object to changes in its state of motion.
- Inertial Mass — The ratio of force to acceleration, indicating resistance to velocity change.
Action Items / Next Steps
- Memorize the equation: Force = Mass × Acceleration.
- Practice calculation questions involving force, mass, and acceleration.
- For higher tier: Understand and be able to define inertial mass.
- Review road transport values for typical speed, acceleration, and force.