Newton

1
Newtons Laws Identifying Forces on objects

• One of the key concepts in Mechanics is
  identifying what forces are acting and drawing a
  Force diagram, also known as a Free Body Diagram

2
Identifying and Drawing forces

• Start by drawing the object. You can either
  sketch the object or draw a dot to represent it.
• For each separate force draw an arrow pointing
  away from the object in the direction that the
  force is acting. For example, typically a
  gravitational force is acting straight down
  (unless the object is floating in space somewhere)

3
Force Diagrams (Free Body Diagrams)

• For each force make the length of the arrow
  approximate the size of the force.
• If 2 or more forces are acting in the same
  direction, indicate 2 different arrow to indicate
  they are different forces.
• Identify each arrow you can write Fg for force
  of gravity and Ff for force of friction, etc.

4
Force Diagrams and Newtons Laws

• So, what good are these diagrams?
• According to Newtons 2nd law, accel Forcenet/
  mass
• We need to determine what the Forcenet is for the
  object.
• Like we did in studying motion, the horizontal
  and vertical forces are always treated separately
  or independently.

5
Forces and Newtons laws

• If an object is not accelerating (looking at
  either vertical or horizontal direction) then the
  net Forces in that direction must add up to zero
• Even if an object is moving at constant speed the
  net forces must be zero in the direction of
  motion.