chp 8 modelling

• Modelling assumption

  A) particle

  
• modelling assumption

  A) rod

  
• modelling assumption

  A) lamina

  
• modelling assumption

  A) uniform body

  
• modelling assumption

  A) inextensible string

  
• modelling assumption

  A) smooth surface

  
• modelling assumption

  A) rough surface

  
• modelling assumption

  A) wire

  
• modelling assumption

  A) smooth and light pulley

  
• modelling assumption

  A) bead

  
• modelling assumption

  A) peg

  
• modelling assumption

  A) air resistance

  
• modelling assumptions

  A) gravity

  
• si units

  Weight or force

  Newtons

  N (= kg ms-2)
• si units

  Acceleration

  Metres per second pe rsecond

  ms-2
• si units

  Speed or velocity

  Metres per second

  ms-1
• si units

  Time

  Seconds

  s
• si units

  Length or displacement

  Metre

  m
• si units

  Mass

  Kilogram

  kg
• The normal reaction acts perpendicular to the surface which an object is resting on. It is equal and opposite to the force exerted on the surface by the object, which is determined largely by gravity and the mass of the object
• The frictional force opposes motion between two ‘rough’ surfaces. Although it is a force, friction does not cause movement in its own direction. It just reduces the effect of another force
• If an object is being pulled along (e.g. by a string), then the force acting on the object is called the Tension
• If an object is being pushed along (e.g. by a rod), then the force acting on the object is called the thrust
• Any object moving through air, fluid or a solid will experience resistance caused by the particles in the way
• Gravity is the force between any object and the earth. The Force caused by gravity acting on an object is its weight
• Buoyancy is the upward force on a body which allows it to float
• A vector is a quantity that has both magnitude and direction
• vectors :

  The vector i represents one unit in the positive x-direction

  The vector j represents one unit in the positive y-direction
• vectors:

  The magnitude of a displacement vector is distance, and the magnitude of the velocity vector is speed
• Fully describe the motion of the particles below:

  The particle is moving to the right and its speed is increasing

  
• Fully describe the motion of the particles below:

  The particle is moving to the right and its speed is decreasing

  
• Fully describe the motion of the particles below:

  The particle is moving to the left and its speed is increasing

  
• Fully describe the motion of the particles below:

  The particle is moving to the left and its speed is decreasing

  
• In vectors:

  You can use Pythagoras’ Theorem to find the magnitude of the velocity (speed)
• In vectors:

  You can use Trigonometry to find the angle between the direction of motion and the unit vector i