PHYSICS Ch. 4 Statics

Statics

• a subdivision of dynamics that deals with objects in equilibrium

• when the forces and torques acting on an object are balanced.

• no net force or net torque is acting on the object.

Stability

how likely an object is to tip over when being pushed or moved

static equilibrium

• a state of equilibrium where an object is at rest

• net force and torque on the system is zero

dynamic equilibrium

• a state of equilibrium where an object is moving at a constant velocity

• net force and torque on the system is zero

centre of gravity (cg)

• the average location of weight of an object and the base of support is the region of ground surface which an object is in contact with

• An object will tip over or fall over when its center of gravity is no longer directly above the base of support.

Stable equilibrium

A system is in stable equilibrium when, if displaced, it returns to its original position. The cg remains within the base of support.

Unstable equilibrium

A system is in unstable equilibrium when, if displaced, it does not return to its original position. The cg is outside the base of support.

Neutral equilibrium

A system is in neutral equilibrium when, if displaced, it remains in its new position, such as a ball placed on a horizontal surface.

torque

• a force that can cause a rotation of objects

• τ = rFsinθ

  • τ (tau) is torque in newton meters (Nm)

  • r is the displacement from the axis to the point of contact of F in meters (m)

  • F is the force in newton (N)

  • θ is the angle between F and r

axis of rotation

• the point through which the object rotates about

• If you apply a force at the axis, the object will move.

• If you apply a force at any other point, the object will rotate around the axis.

right hand rule

• fingers are curled in the direction of rotation, the torque vector points in the direction of the thumb.

• counterclockwise rotation is positive torque

• clockwise rotation is negative torque

Solving problems for statics

F_net = 0 = ∑F

∑τ_clockwise = ∑τ_{counterclockwise}

X and Y component

| F_x | = | F | cosθ

| F_y | = | F | sinθ

Magnitude

Unknown angle

Weight

F_g = mg