Forces, Movement & Changing Shape

What the resultant force is

• The resultant force on an object is the single force that has the same effect as all the individual forces added together, direction included
• It determines:
  • the direction the object will move (or accelerate) in
  • the magnitude of the net push or pull the object actually experiences
• The resultant alone matters for the motion; once you have it, you can ignore the individual forces

Adding forces along a line

• Forces along the same straight line combine by simple addition, taking sign into account:
  • Forces pointing the same way are added together
  • Forces pointing in opposite directions are subtracted
• A final answer is only complete when both magnitude and direction are stated, in newtons and as a compass-style direction or left/right/up/down

Friction inside the resultant

• Friction is the force that opposes motion of an object across or through another material
• On a free-body diagram, a friction arrow points opposite to whichever way the object is sliding
• Drag and air resistance are both special cases of friction: drag inside any fluid, air resistance inside air specifically