Forces & Newton’s First Law Dynamics I Forces & Newton’s First Law

4 Natural Forces Gravity: acts between all masses in the universe and has “infinite” range

Electromagnetic (EM) Force: acts between electrically charged particles and “magnetically charged” poles

Strong Nuclear Force (aka Strong Force): Binds nucleons together (very short ranged but extremely strong)

Weak Nuclear Force (aka Weak Force): Acts between particles (e. g Weak Nuclear Force (aka Weak Force): Acts between particles (e.g. Fermions) and is responsible for radioactive decay.

What is a force? A force is a push or a pull on an object An object’s motion will change with time if the forces acting on it are unbalanced Change in motion  change in velocity Change in velocity  acceleration If the forces are balanced the object’s motion will not change No change in motion  velocity is constant Velocity is constant  acceleration is zero

Field Forces vs. Contact Forces Contact forces happen when objects touch Field forces act at a distance Gravity Electrostatic forces Magnetic forces

Force is a VECTOR! To find out if the forces on an object are balance or unbalanced, we must add them as vectors

Newton’s First Law of Motion An object at rest remains at rest, and an object in motion continues in motion with constant velocity unless the object experiences a net external force “At rest” means zero velocity “Net force” means the forces are unbalanced and do not add up to zero

Inertia The tendency of an object with mass to resist a change in motion is called inertia Newton’s first law is called the law of inertia: it says that without a net force an object’s motion will remain unchanged Mass gives objects the property of inertia The greater the mass, the greater the inertia