Newton's Three Laws of Motion and Basic Rocketry

It is not recommended that you try to teach the nature of Newton’s laws in the primary grades; however, as teachers, we must have a basic understanding of these principles. Understanding them is essential if you are going to help your children make good observations and formulate good “experiments” as they probe the techniques of basic rocketry. These concrete experiences form the groundwork for later development of their understandings.

Newton’s First Law of Motion: When an object is at rest, it tends to stay at rest. When an object is in motion, it tends to stay in motion.

We often refer to this as the principle of inertia. The principle of inertia was originally defined by Galileo.

This basic principle tells us that if we have an object on a table that it will tend to stay there unless an external force acts on it. It will not move unless a force such as a wind acts on it, or if the table is not level and gravity takes it toll.

Likewise, if an object is in motion, it tends to stay in motion. Thus, when our car is traveling at 60 miles an hour, it tends to keep traveling at 60 miles an hour unless we apply an external force by putting on our brakes or stepping on the gas pedal.

Newton’s Second Law of Motion: The relationship between an object’s mass and how quickly it is accelerated depends on the force that acted on it. This relationship is usually shown as a mathematical relationship: force = mass of the object times the object’s acceleration (F = M X A or, simply, F= MA).

Unfortunately, mathematical formulas tend to turn off laymen from basic physics. Stephen Hawking, the theoretical physicist, was told that for every equation heused in a book, he would halve the sales (Hawking, 1993). This is unfortunate because basic relationships such as F = MA help us understand some very basic concepts.

What F = MA tells us is that if I have an object such as a golf ball and I act on it with a force such as a golf club, the ball will be accelerated. If I apply a greater force the next time I hit it, the ball will have greater acceleration and travel even farther than it did the first time. (Interestingly, if we didn’t have friction, in this case the air and gravity, our golf ball would continue forever because of its inertia.)

The mass of the object also plays a role. If instead of hitting a golf ball, we placed a baseball on our tee, the baseball would not be accelerated as much and travel as far because the mass of the baseball is greater than the mass of the golf ball.

Newton’s Third Law of Motion: For every action, there is an opposite and equal reaction.

We see the effect of Newton’s third law when we watch a hamster on an exercise wheel. The hamster is trying to run forward, but the wheel under him travels backward.

We normally relate Newton’s third law to projectiles such as bullets, cannons, and rockets. When a cannon is fired, the cannon ball is projected forward, but there is an opposite and equal reaction of the cannon itself rolling backward. Because the cannon has a much greater mass than the cannon ball, it does not travel as far as the cannon ball. When we shoot a rifle, we refer to the opposite and equal reaction as kickback.