Newton’s Third Law

Forces Contact Forces – Normal, Tension, Friction, Applied, etc. Action-at-a-Distance Forces – Gravity, Electromagnetism Any two objects that are interacting will apply forces on each other. Two objects are involved.

Newton’s Third Law Newton called forces “actions” For every action, there is an equal and opposite reaction

Action-Reaction Pairs All forces come in pairs Every force has an equal and opposite force F g =mg (the gravitational force pulling the book toward the earth) F N =mg (the normal force of the surface pushing up on the book)

F fw F wf

F wa F aw

F rw F wr

F rf F fr

Newton’s Laws Summary 1.Objects in motion tend to stay in motion and objects at rest tend to stay at rest. 2.Objects accelerate when acted upon by an external unbalanced force (a net force). The objects will accelerate proportionally to the force, and inversely proportional to their mass according to this equation: F=ma 3.Every action has an equal and opposite reaction.

Skills you need: 1.Draw Free Body Diagrams 2.Determine Net Force 3.Manipulate and use F=ma 4.Combine F=ma with kinematic equations 5.Understand the basics of tension and pulleys 6.Perform unit analysis 7.Understand how and when to use g=9.8N/kg or 9.8m/s 2

Basic Pulley Question I Find the acceleration of the following system: 500g 350g Frictionless Surface

Basic Pulley Question II Find the string tension in the following system: 500g 350g Frictionless Surface

Intermediate Pulley Question Find the acceleration and tension of the following system if there is 2N of friction on the 500g block due to the surface. 500g 350g

Advanced Pulley Question Find the acceleration of the following system if there is 1N of friction on the 500g block due to the surface. 500g 350g550g Frictionless Surface

Advanced Pulley Question II Find the mass of block M if the system accelerates at 1m/s 2 to the right. 500g M550g Frictionless Surface

Pulleys Redirect Forces

Hanging Pulley 2:1 Advantage

Multiple Pulleys 4:1 Advantage