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FORCES & LOADS

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Forces & Loads

  • a force is an interaction that can change the motion of an object

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Different Types Of Forces

GRAVITATIONAL FORCE

(Gravity)

MAGNETIC FORCE

(Magnets)

MECHANICAL FORCE

(Pushing)

FRICTIONAL FORCE

(Rubbing)

TENSILE FORCE

(Tightening)

COMPRESSIVE FORCE

(Crushing)

ROTATIONAL FORCE

(Turning)

ELECTRICAL FORCE

(Electricity)

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Magnitude & Direction

  • all forces have a magnitude and a direction
    • the magnitude of a force is how strong the force is
    • the direction of the force is the way that it is pushing or pulling

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Vectors

  • we represent forces as vectors
    • (arrows that have both a magnitude and a direction)

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Direction: RIGHT

Magnitude: MEDIUM

Direction: RIGHT

Magnitude: LARGE

Direction: DOWNWARD

Magnitude: TINY

Direction: DOWNWARD

Magnitude: HUGE!

Direction:

Magnitude:

Direction:

Magnitude:

Direction:

Magnitude:

Direction:

Magnitude:

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Vectors

  • The forces are acting in different DIRECTIONS but are equal in MAGNITUDE.
  • We use vectors that are the same size but face away from each other.

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Vectors

  • Both forces are acting in the SAME DIRECTIONS but the second force has double the magnitude.
  • We use vectors that are facing the same direction but are different sizes.

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Newtons (N)

  • We measure force in Newtons (N)
    • named after Sir Isaac Newton,
      • a celebrated mathematician and physicist
      • e.g. it takes about 1 N of force to lift an apple

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Mass vs Weight

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Mass vs Weight

MASS

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Mass vs Weight

  • mass is a measure of the amount of matter in an object
  • weight is a measure of how strong the force of gravity is on that object

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MASS VS. WEIGHT

your MASS is the same whether you are on the Earth or the Moon but your WEIGHT changes

The Moon exerts about �1.6 N per kg of mass

The Earth exerts about �9.8 N per kg of mass

NASA

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MASS VS WEIGHT

  • to pick up an object, you have to overcome the force of gravity that is pulling it to the surface of the Earth

1 kg

you have to generate about �9.8 N OF FORCE �to lift the water bottle off the desk

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Loads

Dead �Load

Live �Load

is a static (not moving) load caused by the weight of the

structure itself

is a static load caused by the weight of the objects that the structure supports

the dead load does not change

Dynamic Load

is any moving load that is not caused by gravity

(e.g. wind, water)

the live load changes as the objects change

the dynamic load changes with the conditions

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