1. 1. Chapter 4 NEWTONS 3rd LAW OF MOTION Action Reaction Pairs Examples Figures from OpenStax College, ancillaries to College Physics. OpenStax College. 21 June 2012. http://cnx.org/content/col11406/latest/, licensed under a CC 4.0 International License, unless otherwise specified.
2. 2. Newtons 3rd Law For every action, there is an equal and opposite reaction. NewtonsLawOfUniversalGravitation.svg; by Dna-Dennis derivative work: Onio72 (talk)) [CC BY 3.0 Unported]
3. 3. Example 1 swimmer pushing on a wall
4. 4. Example 2 Person pushing a cart
5. 5. Check Your Understanding 1 While driving down the road, a firefly strikes the windshield of a bus and makes a quite obvious mess in front of the face of the driver. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the bus? http://www.physicsclassroom.com/Class/newtlaws/u2l4a.cfm
6. 6. Check Your Understanding 1 - Answer The forces are equal! For every action, there is an equal reaction. The fact that the firefly splatters only means that with its smaller mass, it is less able to withstand the larger acceleration resulting from the interaction. http://www.physicsclassroom.com/Class/newtlaws/u2l4a.cfm
7. 7. Check Your Understanding 2 A rifle recoils when it is fired as a result of action-reaction force pairs. A gunpowder explosion creates hot gases that expand outward allowing the rifle to push forward on the bullet. The bullet pushes backwards upon the rifle. The acceleration of the recoiling rifle when compared with that of the bullet is: a. greater. b. smaller. c. the same. http://www.physicsclassroom.com/Class/newtlaws/u2l4a.cfm
8. 8. Check Your Understanding 2 - Answer Correct Answer: B The force on the rifle equals the force on the bullet. Yet, acceleration depends on both force and mass. = The bullet has a greater acceleration due to the fact that it has a smaller mass. http://www.physicsclassroom.com/Class/newtlaws/u2l4a.cfm