Type of Forces

Types of Forces in AS-Level Physics

At AS level, forces are categorized into different types based on how they act and their effects on objects. Here’s a closer look at key force types, including weight, normal contact force, frictional force, resistive force, and upthrust.

Force is the rate of the change in momentum.

1. Weight(W)

• Definition: The force due to gravity acting on an object’s mass.

• Formula: W = mg

Where is the mass of the object (in kg) and is the gravitational field strength ( 9.81 ms^-2 on Earth).

• Direction: Always acts vertically downward toward the center of the Earth.

2. Normal Contact Force

• Definition: The force exerted by a surface perpendicular to the object in contact with it.

• Direction: Acts perpendicular to the surface.

3. Frictional Force(f)

• Definition: The force that opposes the relative motion or attempted motion of two surfaces in contact.

• Formula:

Where mu is the coefficient of friction (static or kinetic) and FN is the normal contact force.

• Direction: Opposes the direction of motion or attempted motion.

• Types:

• Static friction: Prevents motion from starting.

• Dynamic friction: Opposes motion of moving objects.

4. Resistive Force

• Definition: Forces that oppose motion through a medium (e.g., air, water).

• Types:

• Air Resistance (Viscous Drag by air): Opposes motion through the air; depends on speed, shape, and surface area.

• Viscous Drag by liquid: Opposes motion through liquids.

• Direction: Always acts opposite to the direction of motion.

5. Upthrust (Fu)

• Definition:Upthrust is caused by pressure difference on top and bottom surfaces

Where rho is the fluid density, V is the displaced volume, and g is gravitational field strength.

• Direction: Acts vertically upward.

• Example: A boat floating on water experiences an upthrust equal to its weight.

Summary of Directions