COMPLETE REVISION OF CHAPTER FORCES
*** Scalars vs. Vectors.***
Quantities in physics are divided into two categories based on whether direction matters.
● Scalar Quantities: Have magnitude (size) only.
○ Examples: Mass, distance, speed, time, energy, temperature.
● Vector Quantities: Have both magnitude and direction.
○ Examples: Force, weight, displacement, velocity, acceleration, momentum.
Combining Vectors
● Parallel Vectors: If forces act in the same direction, add them. If they act in opposite directions, subtract the
smaller from the larger.
● Non-Parallel Vectors (Tip-to-Tail Method): To find the resultant force (FR) of two perpendicular forces, use the
Pythagorean theorem and trigonometry:
FR=F12+F22
tan(θ)=AdjacentOpposite
2. Types of Forces <3
A force is a push or pull exerted on an object due to its interaction with another object. Forces are measured in Newtons (N).
● Contact Forces: Require physical contact between objects.
○ Friction: A force that opposes motion between two surfaces.
○ Normal Contact Force (Reaction Force): The perpendicular force exerted by a surface on an object resting
against it.
○ Tension: The pulling force transmitted through a string, rope, or cable.
○ Air Resistance / Drag: Friction acting on an object moving through a fluid (like air).
● Non-Contact Forces: Act over a distance via a field.
○ Gravitational Force (Weight): The pull of gravity on a mass.
, ○ Electrostatic Force: Attracts or repels charged particles.
○ Magnetic Force: Attracts or repels magnetic poles.
3. Mass vs. Weight
These two terms are frequently confused but represent fundamentally different concepts.
Characteristic Mass Weight
Definition The amount of matter in an object. The gravitational force acting on an object's
mass.
Property An intrinsic property (never changes based Varies depending on the local gravitational field
on location). strength (g).
SI Unit Kilograms (kg) Newtons (N)
Measurement Tool Electronic balance / Beam balance Spring balance (Newton-meter)
The Formula:
W=mg
Where:
● W = Weight in Newtons (N)
● m = Mass in kilograms (kg)
● g = Gravitational field strength (N/kg or m/s2). On Earth, g≈9.81 N/kg (often rounded to 10 N/kg in O Level).
4. Newton’s Laws of Motion
Newton's three laws form the foundation of classical mechanics, describing how forces dictate motion.
Newton's First Law (Law of Inertia)
An object will remain at rest or continue to move at a constant velocity unless acted upon by a resultant
(net) external force.
*** Scalars vs. Vectors.***
Quantities in physics are divided into two categories based on whether direction matters.
● Scalar Quantities: Have magnitude (size) only.
○ Examples: Mass, distance, speed, time, energy, temperature.
● Vector Quantities: Have both magnitude and direction.
○ Examples: Force, weight, displacement, velocity, acceleration, momentum.
Combining Vectors
● Parallel Vectors: If forces act in the same direction, add them. If they act in opposite directions, subtract the
smaller from the larger.
● Non-Parallel Vectors (Tip-to-Tail Method): To find the resultant force (FR) of two perpendicular forces, use the
Pythagorean theorem and trigonometry:
FR=F12+F22
tan(θ)=AdjacentOpposite
2. Types of Forces <3
A force is a push or pull exerted on an object due to its interaction with another object. Forces are measured in Newtons (N).
● Contact Forces: Require physical contact between objects.
○ Friction: A force that opposes motion between two surfaces.
○ Normal Contact Force (Reaction Force): The perpendicular force exerted by a surface on an object resting
against it.
○ Tension: The pulling force transmitted through a string, rope, or cable.
○ Air Resistance / Drag: Friction acting on an object moving through a fluid (like air).
● Non-Contact Forces: Act over a distance via a field.
○ Gravitational Force (Weight): The pull of gravity on a mass.
, ○ Electrostatic Force: Attracts or repels charged particles.
○ Magnetic Force: Attracts or repels magnetic poles.
3. Mass vs. Weight
These two terms are frequently confused but represent fundamentally different concepts.
Characteristic Mass Weight
Definition The amount of matter in an object. The gravitational force acting on an object's
mass.
Property An intrinsic property (never changes based Varies depending on the local gravitational field
on location). strength (g).
SI Unit Kilograms (kg) Newtons (N)
Measurement Tool Electronic balance / Beam balance Spring balance (Newton-meter)
The Formula:
W=mg
Where:
● W = Weight in Newtons (N)
● m = Mass in kilograms (kg)
● g = Gravitational field strength (N/kg or m/s2). On Earth, g≈9.81 N/kg (often rounded to 10 N/kg in O Level).
4. Newton’s Laws of Motion
Newton's three laws form the foundation of classical mechanics, describing how forces dictate motion.
Newton's First Law (Law of Inertia)
An object will remain at rest or continue to move at a constant velocity unless acted upon by a resultant
(net) external force.
