Unit 2 Review (Dynamics)

Dynamics

• Dynamics is defined as the branch of mechanics detailing the motion of objects or systems under the action of forces.

Systems

• A system is an object or a collection of two or more objects that is treated as having no internal structure. A system approach is often used to find the acceleration (F = ma, according to Newton's Second Law of Motion) in which the total mass of the system is used. 

The Gravitational Field

• The force of gravity on Earth is given by the equation F = mg. M is the mass in kilograms of the object and G is 9.8 m/s/s (However, it is acceptable to use 10 m/s/s on the AP exam). This force is also known as Weight (W) or the Force of Gravity (Fg). If this is the only force exerted on an object, the object is said to be in free fall.

Contact Forces

• Contact forces result from one object or system interacting with another. In AP Physics 1, these forces include tension, friction, normal, and spring. Tension is when an object is pulled by a rope, string or chain. Friction is the opposition to motion (can be kinetic or static). Normal force is when an object is in contact with another object. Last but not least, spring force is when an elastic material is compressed or extended. 

Newton's First Law

• Newton’s First Law states that “every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it." ⬅️➡️

• Inertial Mass - mass that is accelerated (mass in motion)
• Gravitational Mass - mass based on an object’s weight (mass being pulled by the gravitational field) 🌎

Newton's Second Law

• Newton’s Second Law states, “The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.”

• Key equation: Force = mass x acceleration (F = ma)

Newton's Third Law

• Newton’s Third Law states that “For every action, there is an equal and opposite reaction.” 

• In other words, an object cannot exert a force on itself. 
• Action-Reaction Pair: The force exerted on an object is the action, and the force experienced by the object is the reaction. Action-Reaction pairs occur only when two objects interact. (Example: a book pulling down on a table <-> a table pushing up on a book.)