1.2. Forces and Newton's Laws (A2)

Visually: Forces are shown using free-body diagrams (FBDs), where each force acting on an object is represented by an arrow. Arrows indicate magnitude (length) and direction, helping visualize net force and interactions.
Algebraically: Forces are expressed as vectors with components. We apply Newton’s Second Law to each axis to set up equations

Newton’s First Law (Inertia): If ∑F = 0, then a=0: constant velocity or rest.
Newton’s Second Law: ∑F=ma Describes how net force causes acceleration, allowing us to calculate motion from forces or vice versa.
Newton’s Third Law: For every force F_{AB}, there is an equal and opposite force F_{BA}, such that F_{AB} = -F_{BA}. Useful in analyzing interactions, especially in systems of multiple objects.

Newton's three laws of motion
forces as interactions between bodies
that forces acting on a body can be represented in a free-body diagram
that free-body diagrams can be analysed to find the resultant force on a system
the nature and use of the following contact forces
- normal force FN is the component of the contact force acting perpendicular to the surface that counteracts the body
- surface frictional force Ff acting in a direction parallel to the plane of contact between a body and a surface, on a stationary body as given by Ff ≤ μsFN or a body in motion as given by Ff= μdFN where s and d are the coefficients of static and dynamic friction respectively
- tension
- elastic restoring force FH following Hooke's law as given by FH=-kx where k is the spring constant
- viscous drag force Fd acting on a small sphere opposing its motion through a fluid as given by Fd= 6πηrv where η is the fluid viscosity, r is the radius of the sphere and v is the velocity of the sphere through the fluid
- buoyancy Fb acting on a body due to the displacement of the fluid as given by Fb= ρVg where V is the volume of fluid displaced
the nature and use of the following field forces
- gravitational force Fg is the weight of the body and calculated is given by Fg= mg
- electric force Fe
- magnetic force Fm