07 Newtons Second Law

▶️Free video tutorial

Tutorial content:

• Introduce Newtons second law and types of forces.
• Apply Newtons second law.
• Complete six example problems.

Are you ready to delve into the exciting world of particle kinetics? Our tutorial on the kinetics of a particle is here to guide you through the relationship between motion and forces.

In the previous six tutorials, we examined the kinematics of a particle – the geometry of motion without considering the forces that cause or result from that motion. Now, we are ready to consider the kinetics of a particle – the relationship between motion and forces. Forces can cause or be an effect of motion. For example, if a force is applied to a particle through a push or pull, the particle will accelerate. Or, if a particle is moving along a surface, forces such as friction and air resistance can arise.

The foundation of kinetics is Newton’s Second Law, which states that when an unbalanced force acts on a particle, the particle will accelerate in the direction of the force with a magnitude proportional to the particle’s acceleration, where the constant of proportionality is the mass of the particle (F=ma). The mass of the particle is a measure of its resistance to change its velocity, or its inertia.

However, it’s important to note that Newton’s Second Law is based on experimental evidence and has some limitations. Albert Einstein showed that it cannot predict the exact behaviour of a particle approaching the speed of light, and Erwin Schrödinger demonstrated that it is invalid when a particle is the size of an atom and moves close to other particles.

However, in most engineering problems these limitations are not encountered and Newtons second law is still a useful tool for a wide variety of engineering problems, and is unavoidable in a majority of engineering courses.

When applying Newtons second law we will be making these assumptions: the particle is travelling at a velocity far less than the speed of light, is much larger than the size of an atom, and the particle is near the surface of the Earth where acceleration due to gravity can be considered constant.