SPH4U0: Dynamics Unit Review

Physics Grade 12 University Course

Define Dynamics

Dynamics is the study of motion including the forces involved.

Free Body Diagrams Criteria

• forces shown as vectors

• subject is isolated and drawn as a dot

• all forces shown acting directly on the object

• force vectors begin on the object

Newton’s First Law

If there is no net force on an object, then the object will maintain a state of rest or constant velocity.

Newton’s Second Law

If there is a net force acting on an object, then it will accelerate.

Newton’s Third Law

If object A exerts a force on object B, then object be will exert an equal opposite force on object A.

Define net force

It is the sum of all forces acting on an object

When solving for net force, how do you choose a coordinate system (x,y)?

Choose a system that has the direction of motion or attempted direction of motion aligned with the coordinates, including slanted surfaces.

Coordinates can be vertical and horizontal or perpendicular and parallel

How should you approach Newton’s Law problems?

• draw labeled system sketch and free body diagram

• determine net force conditions

  • Ex: F_net = 0 , F_net ≠ 0 

• write net force summation statements in each component direction  

  • Ex. Sum: ∑F_x = F_1x + F_2x + F_3x + … Condition: ∑F_x ≠ 0

  • Ex. Sum: ∑F_y = F_1y + F_2y + F_3y + … Condition: ∑F_y = 0

• Word Problems:

  • Friction not included unless specified

  • Smooth surface indicates no friction

  • Rough surface indicates there is friction

  • Ropes only apply Tension Force - ideal rope

  • Pulleys act to change direction

    • tension is same on either side

    • frictionless - ideal rope

Define Kinetic Friction (F_k)

Is the sliding friction when two surfaces are moving relative to each other

Ex: When driving a car there is kinetic friction between surface of tires and surface of road

Define Static Friction (F_s)

Is the