Lecture 3: Newtons laws

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Lecture 3Newtons laws

• Phys 2101
• Gabriela González

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Newtons laws

• Physics having predictive value!
• Newtons laws two qualitative, one quantitative
• If no net force, no acceleration (either at rest,
  or moving with constant velocity)
• Action and reaction forces are equal and
  opposite.

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2-D motion Uniform circular motion

• Uniform constant speed (angular speed ???
  linear speedv?R)
• Circular constant radius R, velocity vector is
  not constant!
• Acceleration constant magnitude, points towards
  the center
• a v2/R smaller radius with same speed needs
  larger acceleration

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2-D motion Uniform circular motion

• Uniform constant speed
• Circular velocity vector is not constant!
• Acceleration constant magnitude, points towards
  the center
• a v2/R smaller radius needs larger
  acceleration
• A force is needed to produce the acceleration!

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Some special forces
Gravitational force vertical, pointing down,
from center of gravity. Normal force
perpendicular to the surface, making total force
into the surface zero. Tension reaction force
produced by a string Friction force produced by
the surface, parallel to the surface, opposing
motion.
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F ma is all you need!

• The block m1 does not move.
• If m110 kg, what does the spring scale read?
• What are the magnitude and direction of the
  normal force?
• Do the answers change if there is friction?
• What is the tension if ?s0.6? And if it is 0.1?
  

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F ma is all you need!

• If m1m2 10kg, and there is no friction, do the
  objects move?
• What is now the reading in the spring scale?
• If there is friction, do the answers change?