1. WB
Luke is 60 kg. Right before hitting the net, Luke is moving downward at 120 mi/hr (55 m/s). It takes Luke 1.4 s to stop after hitting the net.
Draw a to-scale force diagram for Luke while hitting the net.
Find Luke’s average acceleration while hitting the net.
Find the force that the net exerts on Luke.

2. Investigative Question:
How do the magnitudes of the forces that two interacting objects exert on each other compare?

3. Experiment 1 Summary
Observation: When pulled horizontally from each end, each spring scale had the same force reading.

4. Experiment 2 Summary

5. Experiment 2 Summary
Observation: The same magnitude force causes different accelerations for objects with different masses
(Newton’s Second Law)

6. Newton’s Third Law of Motion –
When two objects interact, Object 1 exerts a force on Object 2 while Object 2 exerts an equal and opposite force on Object 1

7. The forces are Third Law Pairs. One cannot occur without the other.
Unnumbered Figure 3 Page 75
Notice: These forces are exerted on different objects.

8. A life or death scenario:
What could the astronaut do?

9. Newton’s Third Law to the Rescue!
If the astronaut exerts a force on the wrench, the wrench will simultaneously exert an equal and oppositely directed force on the astronaut.
Fwrench on astronaut
Fastronaut on
wrench

10. A dog is sitting on a chair.
Fchair on dog
dog
Fearth on dog
Are these
Third Law Pairs?

11. 3rd Law pairs are on different objects
Fchair on dog
dog
FEarth on dog
Fdog on Earth
chair
Fdog on chair
Earth

12. 3rd Law force pairs cannot exist without their pair
Fchair on dog
dog
Fearth on dog

13. Third Law pairs will always look like…
FA on B
FB on A
and
Reminder: These forces are exerted on different objects, and will appear on different force diagrams.

14. Third Law Force Pair for Jumping