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FORCES

UNDERSTANDING STRUCTURES SYSTEMS IN ACTION

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UNDERSTANDING STRUCTURES AND MECHANISMS �SYSTEMS IN ACTION

3.4  compare, using examples, the scientific definition with the everyday use of the terms work, force, energy, and efficiency

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CURRICULUM

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

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FORCE

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FORCE

  • gravitational force
    • (gravity)
  • magnetic force
    • (magnets)
  • electrical force
    • (electricity)
  • mechanical force
    • (pushing)
  • frictional force
    • (rubbing)
  • tensile force
    • (tightening)
  • compressive force
    • (crushing)
  • rotational force
    • (turning)

there are many different types of forces

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FORCE

  • The MAGNITUDE of a force is how strong the force is

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  • The DIRECTION of the force is the way that it is pushing or pulling

all forces have a magnitude and a direction

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VECTORS

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

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We use vectors that �face away from each other.

but are the same size.

  • The forces are acting in �different DIRECTIONS
  • but are equal in MAGNITUDE.

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  • Both forces are acting in �the same DIRECTION
  • but the second force �has double the MAGNITUDE

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We measure force in NEWTONS (N)

  • Named after �Sir Isaac Newton
    • a celebrated mathematician and physicist
    • EXAMPLE: 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 is a measure of the amount of matter in an object

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weight is a measure of how strong the force of gravity is on that object

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MASS

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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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FRICTION

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FRICTION

  • STATIC FRICTION is the force that holds a stationary object in place

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  • SLIDING FRICTION is the force that acts like a brake when one surface moves across another

friction is the force that resists the motion between two �objects that are �in contact

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STATIC FRICITON

static friction is the force that holds a stationary object in place

You must overcome the static friction holding the textbook to the desk when you try to slide it across the desk surface

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SLIDING FRICITON

sliding friction is the force that acts like a brake when one surface moves across another

the sliding friction is the force that eventually causes the textbook that you pushed to stop

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We use LUBRICANTS between two surfaces that are in contact with each other to reduce the friction

    • this reduces the heat build up that is associated with friction and also reduces wear on parts

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  • gravitational force
  • magnetic force
  • electrical force
  • mechanical force
  • frictional force
  • tensile force
  • compressive force
  • rotational force

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  • Vectors
  • Magnitude
  • Direction
  • Newtons
  • Mass
  • Weight
  • Friction
  • Static Friction
  • Sliding Friction
  • Lubricants

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