2. / A force is a push or a pull that changes motion. / Forces transfer energy to an object. / The force of gravity causes objects to have weight. / The SI unit used to measure force is the newton. (N). / One newton is the force needed to change the acceleration of a 1 kg mass by 1 m/sec 2. / The force of friction acts to slow the movement of objects.

3. / If no other forces act on an object, gravity causes it to accelerate towards the center of the earth at 9.8 m/sec 2. / At terminal velocity, the forces of friction and gravity are equal and opposite on an object. Its speed remains constant. / Projectile motion is the curved path followed by some moving objects. / Projectile motion is caused by the two forces of a horizontal push and downward gravity.

4. / 1st Law: An object at rest stays at rest, and an object in motion stays in motion, unless acted on by an outside, unbalanced force. / 2nd Law: Force = (mass)(acceleration) F = m a / 3rd Law: For every force or action, there is an equal and opposite force or action.

5. Types of Friction /Sliding friction - when two objects slide over one another; determined by object’s weight and type of surface /Rolling friction -when an object rolls over a surface; a smaller force than sliding friction /Fluid friction - when an object moves through a fluid; a smaller force than rolling friction

6. / Momentum is a way to measure “inertia of motion.” It tells how hard it is to stop or start an object’s movement. / Conservation of momentum = the momentum before a collision equals the momentum after a collision (elastic collisions) / A 1000 kg car moving at 28 m/s hits a 4000 kg, stationary truck. How fast will both vehicles be moving after the collision? /Momentum = (mass)(velocity)

7. / An object moving in a circle has centripetal acceleration. / Centripetal force is the force needed to make an object move in a circle / 3 Sources of Centripetal Force;  Friction  Tension  gravitation

8. / According to Newton’s 3rd Law, forces always act in pairs. / Forces may be balanced (equal in amount but opposite in direction). / Forces can also be unbalanced (opposite in direction but unequal in amount). / Balanced forces do not cause a change in motion, but unbalanced forces do !

9. / 4 Universal Forces: - From weakest to strongest :  Gravitational Force  Electromagnetic Force  Weak Nuclear Force  Strong Nuclear Force

10. / Gravitational Force - is the weakest of the universal forces. It depends on the mass of the objects and the distance between them. / Nuclear Forces - The strong force holds the nucleus of an atom together by binding the protons and neutrons. The weak force holds the particles together that make protons and neutrons. /Electromagnetic Forces -may attract or repel. These are much stronger than gravity.