MEPX
Chapter 2 of 10All chapters
  1. 1Describing motion
  2. 2The laws of motion
  3. 3Free body diagrams
  4. 4Friction and normal forces
  5. 5Equilibrium and torque
  6. 6Work and energy
  7. 7Momentum and collisions
  8. 8Circular motion
  9. 9Projectiles
  10. 10Solving problems

Chapter 2 of 10

The laws of motion

Three statements that run everything.

What they say

Without a net force, motion continues unchanged. With one, acceleration equals force divided by mass. Every force has an equal and opposite partner acting on the other body.

  • The first law is really a definition of when the others apply.
  • The third law pair never cancels, because the two forces act on different objects.

Using the second law

Add the forces as vectors, divide by mass, and you have the acceleration. Nearly every problem is that one step wrapped in careful bookkeeping.