{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lec4 - Physics 101 Today Chapter 5 Newtons Third Law First...

Info icon This preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
Physics 101 Today Chapter 5: Newton’s Third Law
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
First, let’s clarify notion of a force : Previously defined force as a push or pull. Better to think of force as an interaction between two objects. Eg. I push on the table, it pushes back on me with an equal and opposite force on me. If on ice (no friction), I’d slide backwards. This force pair constitutes a single interaction. (More egs very soon) You can’t push anything without it pushing back on you ! Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. Newton’s 3 rd Law - often called “ action-reaction
Image of page 2
Eg. Leaning against a wall. You push against the wall. The wall is also pushing on you, equally hard – normal/support force. Now place a piece of paper between the wall and hand. Push on it – it doesn’t accelerate must be zero net force. The wall is pushing equally as hard (normal force) on the paper in the opposite direction to your hand, resulting in zero Fnet . This is more evident when hold a balloon against the wall – it is squashed on both sides.
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Eg. You pull on a cart. It accelerates. The cart pulls back on you (you feel the rope get tighter). Can call your pull the “action” and cart’s pull the “reaction”. Or, the other way around. Newton’s 3 rd law means that forces always come in action-reaction pairs . It doesn’t matter which is called the action and which is called the reaction. Note: Action-reaction pairs never act on the same object
Image of page 4
Examples of action-reaction force pairs In fact it is the road’s push that makes the car go forward. Same when we walk – push on floor, floor pushes us forward. (These forces are frictional). Fun Demo : blow up a balloon and release it. Same principle as rocket
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Clicker Question What is the reaction force to a bat striking a ball? A) the ball’s hit on the bat B) the muscular effort in the player’s arm C) the friction force between the ground and the player’s feet D) gravity E) None of these Answer: A Note that we could call either the action and the other the reaction – it doesn’t matter which one is which.
Image of page 6
Another Question What are the action-reaction pairs once the ball is in the air? First note there are two interactions: (i) one with the earth’s gravity and (ii) the other with the air. (i) Action: Earth pulls down on ball (weight) Reaction: ball pulls up on Earth. (ii) Action: Air pushes ball backwards (air resistance) Reaction: Ball pushes air forwards
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Clicker Question Answer C: They act on different objects .
Image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern