Textbook: 4.5 Homework: WS - Newton’s Third Law

Newton’s Third Law “If object A applies a force on object B, object B applies an equal force on object A in the opposite direction.” |FAB|= |FBA| Ex. A donkey is tied to a cart and tries to pull it forward. How does the donkey move? Ex. Can you put a fan on a sailboat for the times when there is no wind? DEMO.

Applications Walking/Swimming/Driving How Planes Fly Why boxers break their hands Recoil Pg. 148 #53 - 55 Pg. 146 #39

Ex. Two friends (52 kg and 40 kg), are bored out of their minds, sat on chairs with wheels and started pushing each other to experience Newton’s 3rd law. What are their respective accelerations if they exerted a force of 120 N on each other? How far would they travel in 3.5 s?

a) the acceleration of both ducks. 39. Two toy ducks, attached to each other by a string, are being pulled by a very happy guy who just got them as a graduation present. The front duck is 5.0 kg and the back duck is 2.0 kg. If the happy guy pulls them with a force of 10 N and there is no friction, calculate a) the acceleration of both ducks. b) the tension in the string connecting duck 1 and duck 2. a. 1.4 m/s2 b. 2.9 N

Challenge: If the student in Problem 39 receives another duck of mass 1.0 kg from his grandma (he now has three ducks), and he puts the new duck at the front of the row, find a) the acceleration of the three ducks. b) the tension in the string connecting ducks 1 and 2. c) The tension in the string connecting ducks 2 and 3. a. 1.2 m/s2 b. 8.8 N c. 2.5 N