1. Forces Net force ∑F is sometimes known as total force, resultant force or unbalanced force

2. Force Force is an external influence or action on an object that causes the object to change velocity, to accelerate relative to an inertial reference frame. Force is a vector quantity (has magnitude and direction).

3. Contact versus Field Contact Forces Involve Physical Contact between two objects Spring, pulling a wagon, kicking a ball Field Forces Act through empty space, do not involve contact between two objects. Between two masses, between two charges, between magnetic objects

4. Four types of Forces From weakest to strongest these are: Gravitational Electromagnetic Weak Nuclear Strong Nuclear

5. Gravitational Force – between objects The gravitation interaction is a very long-range interaction between particles due to their mass. Some believe this is caused by hypothetical objects called gravitrons.

6. Electromagnetic Force – between objects The electromagnetic interaction is a long range interaction between electrically charged particles involving the exchange of photons.

7. Weak (nuclear) force – arises in certain radioactive decay processes The weak interaction is an extremely short-ranged interaction between sub- nuclear particles. The electromagnetic and weak nuclear interactions are now seen as a single unified interaction called the electroweak interaction.

8. Strong (nuclear) force – between subatomic particles The strong interaction is a long-range interaction between gluons, which themselves consist of quarks, that binds protons and neutrons together to form the atomic nuclei. Some physicists think that strong and electroweak interactions are a single unified interaction.

9. Mass The measure of an object’s inertia. The atomic unified mass unit (u) defined as 1/12th the mass of the carbon-12 atom. 1 u = 1.660540x10-27kg.

10. Inertial Reference Frame If no forces act on an object, any reference frame for which the acceleration of the object remains zero is an inertial reference frame.