Outline of Lesson

The following text is the lesson outline that I handed out to students when I taught two lessons in London Secondary. If you are planning to give a lesson over this subject, this is a format you may wish to follow. I strongly suggest that you try to encourage the students to participate.

The lesson included a student handout (white text). Throughout the lesson, I tried to engage my audience by stating and asking certain questions, seen in blue text, and getting them to 'fill in the blanks'. Red text represents information that students filled into their handouts (copied from my copy off the projector screen).

Lesson Plan:

We will be recalling Newton’s three laws of motion and particularly focusing on Newton’s third law. Many students, including myself, have trouble understanding, grasping and believing the concepts of Newton’s third law. This law is very important, and should be accepted with ease. We experience it in everyday life. Every time we interact with our surroundings we experience this third law. In fact, all moving objects, and stationary objects, experience this law.

Newton’s third law will be demonstrated by several physical collisions between two carts.

Who is this Newton guy, anyway?!

Sir Isaac Newton was born on Christmas Day in Lincolnshire, England 1642 [the same year of Galileo’s death] and died in London, England 1727. Many people associate Sir Isaac Newton for his discovery of gravity, supposedly as he observed an apple drop from a tree.

Though, Newton is also responsible for laying down the fundamental laws of the physical universe. These are the principles that describe how and why things work the way they do. These principles are known as Newton’s Laws of Motion.

Newton laid out the principles of his laws of motion by building on and merging together the work of his great predecessors- such as Galileo Galilei, Copernicus, and Kepler- all by a very young age [early twenties]. He never published anything until years later; only when he was threatened that someone else might publish similar work.

Sir Isaac Newton, the first scientist to have been knighted, was very intelligent, short tempered, little bit of a loner, but a great physicist, an a true genius in mathematics [he discovered the fundamentals for physical optics, theory of gravitation, calculus], but also very modest, and once said “If I have seen further than other men, it is because I stood on the shoulders of giants.”

Newton’s Laws of Motion:

Newton’s first law: The Law of Inertia Does anyone know what Newton's First Law is?

An object in motion tends to stay in motion, and an object at rest tends to stay at rest, unless the object is acted upon by an outside force.

Newton’s second law: The Law of Acceleration Can anyone state Newton's Second Law?

The acceleration with which an object moves is directly proportional to the magnitude of the force applied to the object and inversely proportional to the mass of the object.

In terms of equations: a=F/m or F=ma where a = acceleration, F = force and m = mass

Newton’s third law: The Law of Interaction (The Action-Reaction Law) Who knows Newton's Third Law?

For every action there is an equal and opposite reaction.

Further analysis of the Action-Reaction Law:

The third law stated is correct, but it sometimes can be a little confusing. To actually know what the law means we must understand the meaning of the words “action…reaction”, “opposite” and “equal”

“Action…reaction” means that forces always occur in pairs. Single, isolated forces never happen! The two forces involved are called the ‘action force’ and the ‘reaction force’. These given names are confusing for two reasons:

1) Either force in an interaction can be the ‘action’ force or the ‘reaction’ force.

2) Unfortunately we associate ‘action’ and ‘reaction’ with ‘first an action, then a reaction’.

This is NOT what occurs in the third law. The action force and the reaction force exist at the SAME time.

“Equal” means two things:

1) Both forces are exactly the same size. They are equal in magnitude.

2) Both forces exist exactly at the same time. They are equal in time.

“Opposite” means that the two forces always act in opposite directions à exactly 180 degrees apart.

Does anyone have any questions about the three laws?

Now, keeping these laws in mind, I'm going to physically show you Newton's Third Law through a series of collisions.

[Set up of demonstrations, procedures and what the different components actually do should be explained here and/or before each demonstration]

Collisions:

Students were asked to predict the F vs T graphs for all the following types of collisions. After the prediction, some students were asked to draw their prediction on the board; and then were asked why they think the graph will look like that. The demonstrations were conducted, and discussed.

Colliding the two carts (the carts not sticking together)

Carts of equal masses (roughly 0.6 kg)