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.

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

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

Experiment 2 Summary

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

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

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.

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

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

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

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

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

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.

Third Law Force Pair for Jumping