STATE EXPECTATIONS - FORCES P3.1 – Objects can interact with each other by direct contact (pushes, pulls, friction) or at a distance (gravity, electromagnetic, nuclear) P3.2 – Forces have magnitude and direction. The net force on an object is the sum of all the forces acting on the object. Objects change their speed and/or direction only when a net force is applied. If the net force on an object is zero, there is no change in motion (Newton’s First Law)

P3.4 – The change in speed and/or direction of an object is proportional to the net force and inversely proportional to the mass of the object. The acceleration and net force are always in the same direction. (2ND LAW) P3.3 – Whenever one object exerts a force on another object, a force equal in magnitude and opposite in direction is exerted back on the first object. (3RD LAW)

FORCES & NEWTON’S LAWS 1. A FORCE IS ANY PUSH OR PULL. FORCES CAN CAUSE OBJECTS TO CHANGE DIRECTION, TO START MOVING OR TO STOP MOVING. *FORCES CHANGE MOTION, THEY DO NOT CAUSE MOTION! 2. FORCES ARE REPRESENTED BY VECTORS. WHEN 2 FORCES ARE GIVEN IN THE SAME DIRECTION, THE AMOUNT OF FORCE IS ADDED TOGETHER. 3. WHEN 2 FORCES ACT IN OPPOSITE DIRECTIONS THE AMOUNT OF FORCE IS FOUND BY SUBTRACTING THE SMALLER FORCE FROM THE LARGER FORCE.

4. Net Force = The overall force acting on an object after all of the forces are combined. What is the net force here? What is the net force here? Why is the net force facing to the left? Describe what is occurring in this picture.

5. Balanced Forces occur when the net force is zero. There is no change in motion. 6. Unbalanced forces occur when the net force acting on an object is not zero. Unbalanced forces cause objects to accelerate. *Remember that accelerate has a scientific definition applied here!

7. FRICTION- A FORCE THAT ACTS IN THE OPPOSITE DIRECTION OF A MOVING OBJECT. -FRICTION CAN ARISE FROM TOUCHING SURFACES, BUT AIR CAN ALSO CREATE FRICTION (LIKE AGAINST A MOVING CAR). -FRICTION CAUSES MOVING OBJECTS TO SLOW DOWN AND EVENTUALLY STOP.

8. SIR ISSAC NEWTON (1642-1727), DESCRIBED THE RELATIONSHIP BETWEEN FORCE AND MOTION IN HIS FAMOUS 3 LAWS OF MOTION. 9. INERTIA- THE TENDENCY FOR AN OBJECT AT REST TO REMAIN AT REST OR OBJECTS IN MOTION TEND TO REMAIN IN MOTION. HEAVIER OBJECTS HAVE MORE INERTIA. http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/newtlaws/cci.html 10. NEWTONS FIRST LAW - AN OBJECT AT REST WILL REMAIN AT REST. AN OBJECT IN MOTION WILL CONTINUE MOVING UNTIL ACTED UPON BY A FORCE. BALANCED FORCES!

Newton's 2nd Law

FORCE = MASS X ACCELERATION 11. NEWTON’S SECOND LAW - FORCE = MASS X ACCELERATION EX. THE MASS OF A BALL IS 12 KG. IT IS ACCELERATING AT A RATE OF 2 M/SEC/SEC. HOW MUCH FORCE DOES THE BALL EXERT? STEP 1: F = M X A STEP 2: F = 12KG X 2M/SEC/SEC STEP 3: F= 24KGM/SEC/SEC KGM/SEC/SEC = A NEWTON (N) http://www.ic.arizona.edu/~nats101/n2.html

12. NEWTON’S THIRD LAW- FOR EVERY ACTION THERE IS AN EQUAL AND OPPOSITE REACTION.

How does a rocket liftoff? A large mass of gases are expelled at a very high velocity from the combustion chamber of the rocket engine through specially designed nozzles. The velocity of the exhaust gases is very high and as the gases are expelled, a change in the momentum of these gases takes place in the time the propellant takes to burn. This is the force causing the gases to be ejected. By Newton's third law, this force has a reaction, in the opposite direction, and this is the force, or thrust, that accelerates the rocket.

11. Gravity - the force of attraction between 2 objects due to their mass. -the more massive an object, the more gravitational pull it has. -objects fall to earth because of the pull of earth’s gravity. An object’s acceleration near the surface of the earth is 9.8m/sec/sec.

Notice the large and small rocks both have the same acceleration!

-Which would hit the ground first: a feather or an elephant? http://www.physicsclassroom.com/mmedia/newtlaws/efff.html If you add air resistance, which would hit the ground first: a feather or an elephant? http://www.physicsclassroom.com/mmedia/newtlaws/efar.html 12. Weight and mass are not the same thing. Mass = a measure of the quantity of matter in an object. Weight= mass X acceleration due to gravity (9.8 m/sec/sec)