2025 PhySci Gr 12 Physics Revision Book ENG

Equation of Motion

• The equation of motion: ( v_f = v_i + a\Delta t )

  • Represents the addition of vectors to yield the resultant vector ( v_f ).

  • Must be careful when constructing components of a resultant vector.

Newton's Second Law of Motion

• Basic equation: ( F_{net} = ma )

  • Net force can have one or more components.

  • Example: Two components in the net force.

Example Problem

1. Force Applied: ( F = 10 , N ) to the right, mass ( m = 2.8 , kg ), acceleration ( a = 2 , m/s^2 ).

2. Calculate the frictional force on the box.

Calculation Process

• Don't guess direction for vector addition; use algebra correctly to avoid errors.

Solution Approaches

1. Assuming right to left as positive:

   • ( F_{net} = F + f = ma )

   • ( 10 + f = 2.8 imes 2 )

   • Result: ( f = -4.4 , N ) (( f = 4.4 , N ) left to right based on sign)

2. Assuming left to right as negative:

   • ( F_{net} = F + f = ma )

   • ( -10 + f = (2.8)(-2) )

   • Result: ( f = +4.4 , N ) right to left.

Key Notes

• Sign of final numerical answer indicates vector direction.

• Algebra determined correct scientific information.

Understanding Forces

• Force Diagram Analysis: Focus on free-body diagrams and ensure correct substitutions.

• Force components must reflect physical interactions (ex: gravity, tension).

• Always check against Newton's laws for guidance on net forces.

Newton’s Laws of Motion Overview

First Law:

• An object will remain at rest or in uniform motion unless acted upon by an external force.

Second Law:

• The acceleration of an object is directly proportional to the net force acting upon the object and inversely proportional to its mass.

Third Law:

• For every action, there is an equal and opposite reaction.

Terms and Definitions

• Acceleration: Rate of change of velocity.

• Mass: Measure of the amount of matter in an object.

• Frictional Force: Opposes motion between surfaces.

• Normal Force: Support force exerted perpendicular to the surface.

• Free-body diagram: Visual representation of forces acting on an object.