Newton's Law

Newton's Second Law

"Change of motion is proportional to the force applied, and take place along the straight line the force acts."

Newton's second law for the gravity force - weight - can be expressed as

F = m g (1)

where

F = force (weight)

m = mass

g = acceleration of gravity

The force caused by gravity - g - is called weight. Note! Mass - m - is a property.

The acceleration of gravity can be observed by measuring the change of velocity of a free falling object:

g = dv / dt (2)

where

dv = change in velocity

dt = change in time

A dropped object accelerate to a speed of 9.81 m/s or 32.174 ft/s in one second.

Acceleration of Gravity in SI Units

g = 9.81 m/s²

Acceleration of Gravity in Imperial Units

g = 32.174 ft/s²

Velocity and Distance Traveled of a Free Falling Object

The velocity of a free falling object can be expressed as:

v = g t (3)

where

v = velocity

The distance traveled by a free falling object can be expressed as:

s = 1/2 g t² (4)

where

s = distance traveled by the object

The velocity and distance traveled by a free falling object:

Note! The velocity is achieved without any aero-dynamical resistance (vacuum). The air resistance will be significant for higher velocities or for object with large surface area to mass ratio - feathers or similar.

Newton's First Law

"Every body continues in a state of rest or in a uniform motion in a straight line, until it is compelled by a force to change its state of rest or motion."

Newton's Third Law

"To every action there is always an equal reaction - if a force acts to change the state of motion of a body, the body offers a resistance equal and directly opposite to the force."

Concrete Properties

Properties of normal strength Portland cement concrete

· Density : 2240 - 2400 kg/m³ (140 - 150 lb/ft³)

· Compressive strength : 20 - 40 MPa (3000 - 6000 psi)

· Flexural strength : 3 - 5 MPa (400 - 700 psi)

· Tensile strength : 2 - 5 MPa (300 - 700 psi)

· Modulus of elasticity : 14000 - 41000 MPa (2 - 6 x 10⁶ psi)

· Permeability : 1 x 10^-10 cm/sec

· Coefficient of thermal expansion : 10^{-5 o}C^-1 (5.5 x 10^{-6 o}F^-1)

· Drying shrinkage : 4 - 8 x 10^-4

· Drying shrinkage of reinforced concrete : 2 - 3 x 10^-4

· Poisson's ratio : 0.20 - 0.21

· Shear strain : 6000 - 17000 MPa (1 - 3 x 10⁶ psi)

· Specific heat capacity : 0.75 kJ/kg K (0.18 Btu/lb_m ^oF (kcal/kg ^oC))

Frictional force can be expressed as

F_f = μ N (1)

where

F_f = frictional force (N, lb)

μ = static (μ_s) or kinet