Lesson 2: Forces and Newton's Second Law

In our first lesson, we discussed Newton's first law and how it states that an object's motion only changes when a force acts upon that object. Today, we will cover Newton's second law.

This law states that the rate at which an object's momentum changes is equal to the force acting on the object. All this really means is that if we have an object and we apply a force to it, there is a direct relationship between the amount of force with which we push with on the object and how fast it ends up going.

Think of it this way. We have a light ball, and we softly push it across a table. It will go slowly across the surface of the table. If we take that light ball and push it extremely hard, the ball will speed across the top of the table. Now we take a heavier ball and push extremely hard. This time, however, the heavier ball has more mass and it rolls across the table slower because we have to push harder to make it go as fast as the light ball.

The length of the arrows in this picture represent approximate quantities. The longer the arrow, the larger the quantity is.



This law basically describes a relationship in terms of numbers. Don't get skittish because this is an extremely easy equation. All Newton's second law says is:

Force = (the mass of the object) multiplied by (the acceleration of the object)

So think of it this way. If we have a 1 kilogram ball and we want to accelerate it by 1 meter per second squared (this is the metric unit for acceleration and means that the ball will go 1 meter per second faster every second), we would have to apply 1 Newton (this is the metric unit of force and is acceleration times mass) of force with our arm.

And with that, we will end our lesson for today. So today, think of a few objects and try to imagine how much for it would take to get them moving in a certain direction.