1. Newton’s Third Law Newton’s 3 rd Law 3 rd Law examples Example 4-12 – Two blocks on table Example 4-13 – Atwood’s Machine Block on Inclined Plane Canal Boat ?

2. Newton’s 3 rd Law Whenever one object exerts for on a second object, second object exerts and equal and opposite force on first object –Action–reaction law. –Necessarily acts on different objects –Action reaction pairs not confused with 2 nd law pairs Examples –Force on hand on table, table on hand –Force of hand on wall…. –Force of hammer… –Pedestrian walking…. –Sled example identify 3 rd and 2 nd law pairs –Book on table on earth - identify 3 rd and 2 nd law pairs

3. Action-reaction

4. Again – 3 rd Law 1 st and 2 nd Law forces act on same object! 3 rd Law forces act on different objects!

5. Again – Trying different fonts 1 st and 2 nd Law forces act on: Same Object! 3 rd Law forces act on: Different Objects!

6. Example 4-12 (coupled boxes) Two boxes connect together FBD for each box Tension equal and opposite 3 rd law Accelerations the same Solve simultaneous equations for acceleration, tension Could solve as one block if not interested in tension

7. Example 4-12 (coupled boxes)

8. Example 4-12 (equation solving)

9. Example 4-13 Atwood’s Machine Free body diagram for each block Tensions same by 3 rd law Accelerations locked together (- sign) Equation of motion for each Solve for acceleration Solve for tension Limiting cases

10. Block on Incline FBD Tilted axes Getting the angles F n = mg cosθ F x = mg sin θ a x = g sin θ Get v, x at 2 seconds Limiting cases