Notes on Force and Newton's Laws of Motion

FORCE Lecture Breakdown

• Definition of Force

• Newton’s Laws of Motion

• Types of Forces

• Friction

• Effective Use of Ground Reaction Force (GRF)

NEWTON’S LAWS OF MOTION

Three fundamental laws that form the basis of modern mechanics:

1. 1st Law: Law of Inertia

2. 2nd Law: Law of Acceleration

3. 3rd Law: Law of Reaction

1ST LAW: LAW OF INERTIA

• Equation: $ext{ΣF} = 0$

• Concept of Inertia:

  • Refers to a body's reluctance to change its state of motion.

  • Tendency to maintain its state of rest or uniform motion.

  • Higher mass (kg) corresponds to higher inertia.

• Statement: "An object will remain at rest or in motion unless acted upon by a net external force."

2ND LAW: LAW OF ACCELERATION

• Statement: "The change in motion of an object is proportional to the force impressed; directed along the straight line in which it is impressed."

• Equation: $F = ma$

• Where:

  • $F$ = force (measured in N)

  • $m$ = mass (measured in kg)

  • $a$ = acceleration (measured in m/s²)

Applications of 2nd Law

• Constant Mass & Applied Force:

  • $F = ma$

  • As force increases, acceleration also increases if mass remains constant.

• Constant Acceleration:

  • For a given applied force over constant mass, acceleration is consistent.

• Constant Force:

  • A set force will yield varying acceleration based on changes in mass.

3RD LAW: LAW OF REACTION

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

• Explanation:

  • If object A exerts a force on object B, then object B exerts an equal but opposite force on object A.

• Equation: {ΣF}{A to B} = - {ΣF}{B to A}

• Description:

  • Action: Force exerted downwards and backwards.

  • Reaction: Force exerted upwards and forwards.

  • These forces are not limited to ground reaction forces (GRF) only.