Newton also observed another property that an object’s mass affects how an object’s motion changes with the application of an unbalanced force.

The relationship between the force on an object, its mass, and how its motion changes is called Newton’s Second Law.

The motion of an object is determined by all of the forces acting on it. The greater the mass of the object, the greater the force needed to achieve the same change in motion.

Newton’s Second Law summarizes this with the formula F = ma, where F is the force, m is the mass, and a is the acceleration.

If we want to solve for acceleration, we change the formula around so that a = F/m. This shows the relationship between force and mass on acceleration.

If mass is held constant (not changed), then as force increases, the acceleration increases. These are directly related.

Mass and acceleration are inversely related. This means that if force is held constant, then as the mass increases, the acceleration would decrease.

Think about two vehicles – one is a small sports car and the other is a dump truck. According to this formula, the vehicle with more mass (the dump truck) would accelerate more slowly than the vehicle with less mass (the sports car) if the same force is applied.

As an object accelerates (changes speed or direction), an unbalanced force is acting on it. If there are multiple forces on the object, the acceleration is proportional to the overall force.

One important force to consider is the force of gravity. Gravity will be discussed later, but for now, you need to understand that gravity is a force of attraction between things that have mass. Gravity is the force that pulls you towards the center of the planet.