1. Summary : 4. Newton's Laws

2. Newton’s 1 st law of motion (definition of inertia) : Newton’s 2 nd law of motion : Newton’s 3 rd law (conservation of momentum) : Normal force n : contact force acting normal to contact surface. m in f = m a is the inertia mass. Weight = force of gravity on mass:m is gravitational mass inertial frame only Special Cases

3. The Fundamental Forces The fundamental forces : Gravity: large scale phenomena Electroweak force Electromagnetic force: everyday phenomena Weak (nuclear) force Strong (nuclear) force 1 10 25 10 36 10 38

4. Free Body (Force) Diagram Keep only features relevant to the dynamics. Replace all objects by points upon which forces act. Represent all forces by vectors.

5. 1.Identify all forces on object 2. Skier reduces to dot 3.Draw forces as vectors on dot Force from ground n Gravity F g Free-body diagram n FgFg

6. Example 4.4. Pushing Books 2 books lie on frictionless horizontal surface. You push with force F on book of mass m 1, which in turn pushes on book of mass m 2. What force does the 2 nd book exert on the 1 st ? Acceleration of books : Net force on 2 nd book : Force exerted by 2 nd book on the 1 st

7. Normal force n : contact force acting normal to contact surface. 3 rd law also applies to non-contact forces such as gravity. Not a 3 rd law pair Normal force F net  0