1. Newton’s First Law of Motion
Unit b - Dynamics
Newton’s First Law of Motion

2. What is Dynamics?
Dynamics: is the study of forces, forces provide an explanation for WHY objects move
A FORCE: is simply a push or pull
Force is a vector quantity; it has both a magnitude and direction
Force is measured in NEWTONS (N)
Examples of Forces:
Gravitational
Electric
Magnetic
Weak and Strong nuclear

3. Newton’s Laws of Motion
NEWTON’S FIRST LAW OF MOTION:
“A body continues in its state of rest or uniform motion in a straight line unless acted upon by an external unbalanced (net) force”.
The unbalanced (or net force) on an object is the sum of all of the forces acting on the object.

4. Sample Problems – Net Force
A force of 2.0N east and a force of 3.0N east acts on an object. What is the net force on the object?
A force of 2.0 N east and a force of 3.0 N west acts on an object. What is the net force on the object?
A force of 2.0 N east and a force of 3.0 N south acts on an object. What is the net force on the object?

5. Illustrations Of Newton’s 1st Law of Motion
Holding a bag in your hand as an elevator accelerates upward
Standing on a subway that speeds up or slows down
A car turns a sharp corner to the left

6. Inertia and Momentum
Newton’s first law is also called the Law of Inertia. Inertia is the tendency of a body to resist changes in motion. The idea of inertia is also called momentum.
Momentum varies directly with the mass of the object
Momentum varies directly with velocity

7. REVIEW UNIT A EXAM