Forces: Newton's Second Law

Forces: Newton’s Second Law

Newton’s Second Law

Basic Understanding

  • Newton’s second law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

  • In other words, larger forces lead to greater accelerations, and larger masses lead to smaller accelerations.

  • The law can be expressed with the formula: F = m*a, where F represents the net force, m the mass of the object, and a the acceleration.

Force, Mass, and Acceleration

  • The net force is equal to the mass of the object multiplied by the acceleration.

  • Mass is an object’s quantity of matter, measured in kilograms (kg). It should not be confused with weight, which is a force due to gravity.

  • Acceleration is the rate of change of velocity of an object. It is generally expressed in metres per second squared (m/s²).

  • It is important to remember that if an object is accelerating, it does not mean that it is necessarily getting faster - it could be slowing down, i.e., decelerating.

Applying Newton’s Second Law

  • The second law shows that if more force is applied to an object, it will accelerate more rapidly.

  • On the other hand, if an object has more mass (i.e., it’s heavier), it will accelerate less quickly for a given applied force.

  • If the net force acting on an object is zero (i.e., the forces are balanced), the object will stay at rest if it is at rest, or continue moving at a constant velocity if it is in motion.

Examples of Newton’s Second Law

  • Vehicle dynamics is a good example of the application of Newton’s Second Law. More force (in the form of engine power) will cause a car to accelerate more quickly, but a heavier car will accelerate more slowly than a lighter one might with the same power output.

  • The law also applies to astronautics; rockets must overcome the force of gravity (which increases the effective weight of the rocket) to accelerate in order to leave the Earth’s atmosphere.