# 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.