1. Newton’s Laws of Motion
Force: A vector quantity representing a “push” or “pull” on an object Units: Newton (N)
Mass: A scalar quantity representing an object’s tendency to stay at rest or stay in constant motion (“Inertia”) Units: kilogram (kg)
Sir Isaac Newton developed three very important laws dealing with force and mass.

2. Newton’s Laws of Motion (2)
Newton’s First Law: An object continues in a state of rest or in a state of motion in a straight line at constant speed unless acted upon by a net force (aka - law of Inertia)
Newton’s Second Law: When a net force (F) acts on an object of mass ‘m’, the resulting acceleration of the object is:
Directly proportional to the net force.
Inversely proportional to the mass

3. Newton’s Laws of Motion (3)
In equation form:
Newton’s Third Law: Whenever one body exerts a force on another body, the second body exerts an equal but oppositely directed force on the first body.

4. Newton’s Laws of Motion (4)
Free-Body Diagrams: A separate diagram for each object in a problem showing all forces acting on the object.
Ex. One person pushes a 100kg crate with 300N of force to the east, another pushes with a force of 325N also to the east. The friction between the crate and the floor causes an opposing force of 490N. Draw the free-body diagram, then calculate the acceleration of the box.

5. Newton’s Laws of Motion (5)
Solution:
F = 300N + 325N - 490N =135N
490N
300N
325N

6. Newton’s Laws of Motion (6)
Forces are VECTORS , so for example:
If F = 100N at 30°, then it is equivalent to say that Fx = (100N)(cos30°) = 87N
Fy = (100N)(sin30°) = 50N
So, when using Newton’s Second Law when forces are at arbitrary angles, we must break the problem into ‘x’ and ‘y’ sections:
Fx = max and Fy = may

7. Newton’s Laws of Motion (7)
Example:
1. Two forces act on a 20 kg block: F1 = 40.0N at 60° north of east, and F2 = 10.0N due east. Initially, before forces are applied, the block is at rest on a flat surface without friction.
(a) How far has the block moved 10 s after the forces begin acting on it?
(b) What is the final velocity after 10 s?