Forces & Newton’s Laws — A/L Physics

What must I remember about Forces & Newton’s Laws?

• Newton's First Law (Inertia): A body remains at rest or continues to move with constant velocity unless acted upon by a non-zero resultant net external force.
• Newton's Second Law: The rate of change of momentum is directly proportional to the applied resultant force and takes place in the direction of the force: F = dp/dt = d(mv)/dt = ma (when mass m is constant).
• Newton's Third Law: When body A exerts a force on body B, body B simultaneously exerts an equal and opposite force on body A (F_AB = -F_BA); action-reaction pairs NEVER act on the same body.
• Linear Momentum & Impulse: Momentum p = mv; Impulse J = ∫ F dt = F_avg Δt = Δp = mv - mu; Conservation of Linear Momentum: Total momentum of an isolated system remains constant (∑ p_initial = ∑ p_final).

Test yourself (1 minute)

1. Action-Reaction Criteria

   1) Equal magnitude; 2) Opposite direction; 3) Same nature of force (both gravitational, both contact, etc.); 4) Act on TWO DIFFERENT BODIES simultaneously.

2. Elastic vs Inelastic Collisions

   In ALL collisions, total momentum is conserved; Kinetic Energy is conserved ONLY in Elastic collisions (e = 1); In perfectly inelastic collisions, bodies stick together (e = 0, maximum KE loss).

3. Apparent weight in elevators

   Accelerating upward with 'a': R = m(g + a); Accelerating downward with 'a': R = m(g - a); Free fall (a = g): R = 0 (weightlessness).

Practise Forces & Newton’s Laws questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 2: Mechanics

What should I study first?

What comes next?

Next in the syllabus

Where does Forces & Newton’s Laws fit in the syllabus?

Unit 2.2 · Year 1 · Term 1