Basic Concepts

Diagram of bottle rocket: 

• Newton’s 1st Law - Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. 
• This we recognize as Galileo’s concept of inertia, and this is often termed simply the "Law of Inertia."
• Newton’s 2nd Law – If an unbalanced (net) force acts on an object, that object will accelerate or decelerate in the direction of the force
• Newton’s 3rd Law – For every action force, there is an equal and opposite reaction force. A body at rest is considered to have zero speed (a constant speed).
• Any force that causes a body to move is an unbalanced force. Any force, such as friction, or gravity, that causes a body to low down or speed up, is an unbalanced force. This law can be shown by the following formula:
• Force = mass x acceleration 
• F = ma
• F is the unbalanced force (vector)
• m is the object’s mass (scalar)
• a is the acceleration that the force causes (vector)
• Force and acceleration are both vector quantities. In this law, the direction of the force vector is the same as the direction of the acceleration vector, thus the force and direction of the rocket are the same in two directions: when ascending into the air and descending to the ground.
• Vector Quantity: In accordance with Newton’s Second Law, a vector is a quantity that has two aspects. It has a size, or magnitude, and a direction. Force, acceleration, velocity, displacement, gravitational field, torque, electric, and magnetic fields are all examples of vectors.
• Scalar Quantity: This is a quantity that has only size and if a quantity has only a size, it is called a scalar. Mass, distance, speed, time, and temperature are all examples of scalars. 
• Visit this NASA website for more information:  http://exploration.grc.nasa.gov/education/rocket/newton1r.html