Forces: Newton's Second Law – GCSE Physics (Triple) AQA Revision

Forces: Newton’s Second Law

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.

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.

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.

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.