How do we apply Newton’s Second Law (F = ma) in problems involving friction?

• The?coefficient of friction?combined with?F?=?ma?allows you to determine an object's motion where friction is involved in a problem
• For problems where the surface is horizontal:

Step 1. If necessary,?resolve?any angled forces into vertical and horizontal components

Step 2. Calculate the normal reaction force?R

• • Be careful – if there are vertical forces other than gravity these will affect the value of?R
  • with a horizontal surface?R?will always be directed vertically upwards
  • the magnitude of?R?will be such as to make the?total?make the?total?vertical force on the object zero

Step 3. Calculate?F_MAX=?μR?and find the?resultant?(total force) of all the horizontal forces on the object

• • Remember – if the resultant of the other horizontal forces is less than or equal to?F_MAX?then friction will exactly balance those forces out and the object will remain stationary

Step 4. Use?F = ma?to determine the acceleration of the object

• For non-horizontal surfaces see the notes on?inclined planes