KINEMATICS 1 KUS objectives BAT understand the modelling

KINEMATICS 1 KUS objectives BAT understand the modelling cycle BAT understand assumptions made in a model Starter:

Objects moving under acceleration Real world model If a model does not produce reliable conclusions we usually go back to the assumptions made in the simplification.

Mathematical models in MECHANICS Some key assumptions we usually make are: An object is modelled as a PARTICLE. A body whose dimensions are so small they can be represented as a single point. A SMOOTH SURFACE is one which offers negligible resistance to the motion of a body sliding across it. e. g. a sheet of ice. A LIGHT INELASTIC STRING is a string of no weight whose length remains the same whether motion is taking place or not A UNIFORM ROD is one in which equal lengths have equal masses. Width and height are negligible, a rod is assumed to have a length only.

WB 1 Think about the motion of a cricket ball thrown through the air. In the simplest model we would assume: 1. 2. 3. 4. the ball is modelled as a particle acceleration due to gravity is constant the motion of the ball takes place in a vertical plane the only force acting on the ball is weight The motion of the ball would be a symmetrical curve (parabola). However, in real life the ball would describe an asymmetrical curve. What is the ‘limitation’ of the last assumption in the list? If the only force acting on the ball is weight then air resistance is ignored

WB 2 Think about the motion of a vehicle along a road. In the simplest model we would assume: 1. 2. 3. 4. 5. 6. The road is perfectly straight the vehicle is modelled as a particle acceleration due to the engine is constant the motion of the vehicle takes place in a vertical plane No other forces act on the vehicle Changes of acceleration/velocity happen instantaneously What are the ‘limitations’ of assumptions 5 and 6 in the list? 5. Friction from the road surface is ignored 6. The reaction time of the driver and the vehicle are ignored

KINEMATICS 1 KUS objectives BAT understand the modelling cycle BAT understand assumptions made in a model

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