2. FORCE – A PUSH OR A PULL THAT CAUSES THE CHANGE IN MOTION OF AN OBJECT THERE ARE FOUR FUNDAMENTAL FORCES IN NATURE: 1)GRAVITATIONAL FORCE – IS ALWAYS POSITIVE – CAN ACT AT LONG DISTANCES 2)ELECTROSTATIC FORCE – CAN BE POSITIVE OR NEGATIVE – CAN ACT AT LONG DISTANCES – FORCE IN CHEMICAL BONDS 3)STRONG NUCLEAR FORCE – ACTS AT VERY SHORT DISTANCES (10 -15 METERS) – HOLDS THE NUCLEUS TOGETHER 4)WEAK NUCLEAR FORCE –ACTS AT EVEN SHORTER DISTANCES (10 -18 METERS) – INVOLVED IN BETA DECAY

3. THERE ARE OTHER TYPES OF FORCES, BUT THEY ARE ALL RELATED TO THESE FOUR. THE UNIT THAT WE USE TO MEASURE FORCE IS THE NEWTON, WHICH IS THE AMOUNT OF FORCE NECESSARY TO ACCELERATE 1 kg OF MATTER 1 meter/sec 2. FORCE IS A VECTOR QUANTITY. THE DIRECTION THAT THE FORCE IS ACTING CAN BE SHOWN AS AN ARROW WITH THE LENGTH PROPORTINAL TO THE MAGNITUDE AND THE DIRECTION POINTING TOWARDS THE DIRECTION THE FORCE IS ACTING.

4. FORCE AS A VECTOR QUANTITY

5. THERE ARE METHODS FOR ADDING MORE COMPLICATED COMBINATIONS OF VECTORS. THE NET FORCE IS THE RESULTANT FORCE (VECTOR) AFTER ADDITION OF THE INDIVIDUAL FORCE VECTORS.

6. IF THE NET FORCE IS ZERO, THE OBJECT IS EITHER STATIONARY OR MOVING AT CONSTANT VELOCITY.

7. GRAVITY! IT’S NOT JUST A GOOD IDEA. IT’S THE LAW! FORCE OF GRAVITY = g x m 1 x m 2 d 2

8. FORCE OF GRAVITY = g x m 1 x m 2 Where g = gravitational constant = 9.8 m/sec 2 m 1 and m 2 = masses of objects involved d = distance of separation in meters d2d2

9. THE FORCE OF GRAVITY IS ACTUALLY WEAK COMPARED TO THE OTHER FORCES. HOWEVER, IN THE UNIVERSE, MASSES ARE VERY LARGE, SO IT IS A SIGNIFICANT FORCE. FOR EXAMPLE: MASS OF EARTH = 5.97 X 10 24 kg MASS OF SUN = 2.0 X 10 30 kg MASS OF BLACK HOLE = 4 solar masses, 15 mi. diameter Sagitarius A* = 1300 solar masses

10. WEIGHT IS A MEASURE OF THE FORCE OF GRAVITY ON AN OBJECT. SINCE THE FORCE OF GRAVITY VARIES, DEPENDING ON POSITION IN SPACE, OBJECTS WILL HAVE DIFFERENT WEIGHTS ON DIFFERENT BODIES IN THE SOLAR SYSTEM. EXAMPLES: EARTH150 lb MOON24.9 lb MARS56.5 lb JUPITER355 lb SUN 4061 LB Your mass would not change.

11. FOR FALLING OBJECTS, THE ACCELERATION DUE TO GRAVITY IS 9.8 M/SEC 2. WHAT THIS MEANS IS THAT IF AN OBJECT STARTS WITH A VELOCITY OF 0, AT THE END OF 1 SECOND, THE VELOCITY WILL BE 9.8 m/sec. THE VELOCITY AT ANY TIME IS GIVEN BY: V = gt

12. IN OUR DISCUSSIONS SO FAR, WE ARE IGNORING AIR RESISTANCE. IF AIR RESISTANCE IS NEGLIGIBLE, OBJECTS WILL FALL AT THE SAME RATE. THIS BRINGS US TO PROJECTILE MOTION. A PROJECTILE IS AN OBJECT UPON WHICH THE ONLY FORCE IS GRAVITIY. OR, A PROJECTILE IS ANY OBJECT THAT ONCE PROJECTED OR DROPPED CONTINUES IN MOTION BY ITS OWN INERTIA AND IS INFLUENCED ONLY BY THE DOWNWARD FORCE OF GRAVITY.

15. Inertia is the resistance of any physical object to any change in its state of motion, including changes to its speed and direction. It is the tendency of objects to keep moving in a straight line at constant velocity.