1. CHAPTER 4 FORCES

2. Force  What do you think a force is?  It is a push or pull on an object  A force is a vector quantity

3. Contact vs. Field  Contact force – object from external world touches the system exerting a force on it  Field Force – force that is exerted without an object “touching” the object agent – applies the force system – what the force gets applied to

4. Types of Forces  Gravitational – attractive force that exists between all objects. Weakest of the forces  Electromagnetic (electroweak) – force that gives materials their strength (bend, stretch, shatter). Combine electric and magnetic forces Weak – type of electromagnetic force that is primarily responsible for radioactive processes (decay of a nucleus to a lower energy level)

5. continued –The unification of the electromagnetic and weak force is still under testing. Current predictions have been confirmed at high energy levels.  Strong nuclear – force that holds together the particles inside the nucleus (only acts over the size of the nucleus). Strongest of the forces.

6. FREE BODY DIAGRAMS  Also known as Force Diagrams  A physical model (sketch) of the forces acting on an object (system)

7. Combining Forces  Net force – vector sum of all forces acting on an object  Equilibrium – net force equals zero

8. NEWTON’S LAWS OF MOTION  First Law – an object with no net force acting on it remains at rest or moves with constant velocity in a straight line.

9. Inertia  The tendency of an object to resist motion  Large mass, large inertia  Small mass, small inertia

10. NEWTON’S LAWS OF MOTION  Second – the acceleration of a body is directly proportional to the net force on it and inversely proportional to its mass a = F/m

11. What are Fig Newton's? If you don’t know this don’t worry! However, you should know the units of force!

12. What are the units of force anyway?  Since we know F = ma, you should be able to figure it out  To accelerate 1 Kg at 1 m/s 2 is one Newton –NOT fig newtons, just Newtons

13. ???Questions???  If you don’t have any, I have one  What did Tennessee? The same thing Arkansas.

14. Now for the equation!  You already know it. F=ma KEEP IN MIND YOU SHOULD ALREAD KNOW HOW TO FIND ACCELERATION

15. NEWTON’S THIRD LAW OF MOTION  When one object exerts a force on a second object, the second exerts a force on the first that is equal in magnitude, but opposite in direction  Often referred to as “for every action there is an equal and opposite reaction”  Action-reaction forces

16. 3 rd Continued F AB = - F BA

17. MASS VS. WEIGHT  In one corner we have mass weighing in at, wait (no pun intended)  Mass is not a weight, it is how much matter an object has  And in the other corner we have weight weighing in at W = m g

18. continued  The weight of an object is proportional to its mass  Weight is the gravitational force of an object, and this depends where you are located  Mass remains the same no matter where you are located

19. EQUATION F g =m g

20. 2 kinds of MASS  Inertial mass – the ratio of the net force (sum of all the forces) to the acceleration of the object  Gravitational mass – comparison of a known mass with an unknown mass  You use a pan balance to do this

21. ???QUESTIONS???