FUNdamental Forces

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FUNdamental Forces FBDs
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What is a force?

• A push or a pull on an object.

• Lets demonstrate
• Pick a partner (size appropriate)
• Stand 50cm apart from each other (feet shoulder
  width apart).
• Put your hands out to your sides with your palms
  facing your partner.
• Now the object is to keep your balance and knock
  your partner off balance by avoiding their
  attempts or by you hitting their hands ONLY.

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Strong Nuclear Force

• It has the shortest range, meaning that particles
  must be extremely close before its effects are
  felt.
• Its main job is to hold together the subatomic
  particles of the nucleus .
• Strongest of the 4 fundamental forces.

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Electromagnetic Force

• There are two kinds of electrical charge -
  positive and negative.
• The electrical force can be either attractive or
  repulsive - like charges repel, opposite charges
  attract.
• Although the Electromagnetic force is of order
  1039 times stronger than Gravity, it is not as
  apparent because of its dual (attractive/repulsive
  ) nature
• 2nd strongest of the 4 fundamental forces

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Weak Nuclear Force

• It causes radioactive beta decay and other
  subatomic reactions.
• The particles that carry the weak force are
  called weakons (or intermediate vector bosons).
• 3rd Strongest of the 4 fundamental forces.

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Gravitational Force

• It is a purely attractive, long-range force.
• We will learn Newtons Law of Universal
  Gravitation tomorrow (stay tuned)
• Weakest of the 4 fundamental forces

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Electroweak Force

• A force that unifies the electromagnetic and weak
  nuclear forces under conditions of extreme
  temperature prevalent much earlier in the history
  of the universe.
• Physicists concluded that the weak and
  electromagnetic forces have essentially equal
  strengths. This is because the strength of the
  interaction depends strongly on both the mass of
  the force carrier and the distance of the
  interaction.

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How is a force measured?

• A Newton (N) is the unit of force
• 1 N 1 kg m
• s2
• By looking at the units, the equation for force
  is Fma (your new best friend)
• Forces are usually measured using a spring scale

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Free Body Diagrams (FBDs)

• Here is the step by step how to draw one
• Draw a north arrow and a scale
• Sketch of the object (dont be too detailed)
• Locate the approximate centre of the object and
  put a dot there.
• Draw on the force arrows to represent each force
  on the object (just like vector diagrams).
• Do NOT include the forces that the object exerts
  on other objects.

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Common Forces

• Normal Force (FN) acts on an object
  perpendicular to the surface it is resting on
• Friction (Ff) ALWAYS opposes motion
• Gravity (FG) related to mass and is straight
  down
• Applied (FApp) given by a external body

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Example FBDs
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Adding Non-Collinear Forces

• It is the same as adding vector quantities that
  we did in chapter 1, but now we can use
• Tail to Tip method again.
• Trig ? - Sine Law
• Cosine Law ? c2 a2 b2 - 2abcos(C)

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Homework

• p. 119 1,2
• Have Fun ?