Table of Contents
Newton Second Law
Newton Second Law states that the acceleration of an object is directly proportional to the net force acting upon it and inversely proportional to its mass. This law is the cornerstone of classical mechanics and allows us to predict how objects move when forces are applied.
The law applies from thrown baseballs to launching rockets. It explains why a heavy truck accelerates more slowly than a lightweight car under the same engine force, and why a tennis ball responds dramatically to a racket compared to a bowling ball.
F = ma Formula
Where a is acceleration in m/s², F is net force in Newtons, m is mass in kg, mu is the coefficient of kinetic friction, and g is 9.80665 m/s².
Force and Acceleration Examples
| Scenario | Force (N) | Mass (kg) | Acceleration |
|---|---|---|---|
| Shopping cart | 50 | 25 | 2.0 m/s² |
| Car engine | 5,000 | 1,500 | 3.3 m/s² |
| Rocket thrust | 3,500,000 | 500,000 | 7.0 m/s² |
| Baseball pitch | 90 | 0.145 | 621 m/s² |
FAQ
What counts as net force?
Net force is the vector sum of all forces acting on the object, including applied forces, gravity, friction, air resistance, tension, and normal force. If forces balance out (net = 0), the object moves at constant velocity or stays at rest per Newton first law.
Does mass change affect acceleration?
Yes, doubling mass while keeping force constant halves the acceleration. This inverse relationship explains why rockets become faster as they burn fuel and lose mass, described by the Tsiolkovsky rocket equation for variable-mass systems.
What is the difference between weight and mass?
Mass is the amount of matter measured in kg, constant everywhere. Weight is the gravitational force W = mg measured in Newtons, varying with local gravity. On the Moon your mass stays the same but your weight drops to about one-sixth of its Earth value.