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CIE AS/A Level Physics Unit : 3.2 Non-uniform motion Study Notes | IITian Academy

CIE AS/A Level Physics Unit : 3.2 Non-uniform motion Study Notes - 2025-2027 Syllabus

CIE AS/A Level Physics Unit : 3.2 Non-uniform motion Study Notes

CIE AS/A Level Physics Unit : 3.2 Non-uniform motion Study Notes at  IITian Academy  focus on  specific topic and type of questions asked in actual exam. Study Notes focus on AS/A Level Physics  Study Notes syllabus with Candidates should be able to:

  1. show a qualitative understanding of frictional forces and viscous/drag forces including air resistance (no treatment of the coefficients of friction and viscosity is required, and a simple model of drag force increasing as speed increases is sufficient)
  2. describe and explain qualitatively the motion of objects in a uniform gravitational field with air resistance
  3. understand that objects moving against a resistive force may reach a terminal (constant) velocity

AS/A Level Physics Study Notes- All Topics

3.2.1 show a qualitative understanding of frictional forces and viscous/drag forces including air resistance (no treatment of the coefficients of friction and viscosity is required, and a simple model of drag force increasing as speed increases is sufficient)

  • Frictional forces are the forces that oppose the motion of an object.
  • When two surfaces come in contact with each other (see in figure)
                                                                                            
  • Frictional forces arise from (a) chemical bonding from opposing points when they come into contact.
  • (b) One peak physically blocking the motion of a peak on the opposing surface, even for surfaces which are apparently smooth.
  • Frictional forces are dissipative in nature as energy is required to overcome them.
  • The work done in overcoming friction is wasted in he form of thermal energy (heat) produced.
  • Viscous force: It is the frictional force acting on a body moving in fluids (i.e., liquid or gas). 
  • It arises because of the attractive forces between fluid molecules.
  • Viscous forces are also known as Drag forces.
  • Drag forces are not created by any force fields. 

  • In order to experience a drag force, an object has to come into physical contact with the fluid medium.

  • A drag force is produced by the deviation or difference in velocity between the fluid and the object.

  • Drag Equation is used to find the force of drag on an object due to motion through an enclosed fluid system.

  • Drag force is proportional to the velocity of the object, therefore, increases with the increase in velocity.

  • Examples of drag force include resistance on moving vehicles, floating objects, resistance during a storm or heavy wind, resistance on gliders and parachutes.

3.2.2 describe and explain qualitatively the motion of objects in a uniform gravitational field with air resistance

 

                                                                             

 
  • Consider an object falling in air in the presence of uniform gravitational field.
  • In this case, two kind of forces are being applied : force due to gravitational field (downwards) and force due to the air resistance (upwards).
  • Thus, the resultant force is the difference between the gravitational force and drag force.
  • Therefore, the object does not accelerate uniformly.
  • The acceleration is achieved till the force due to gravitation and the drag force balance out each other and at this, point the object reaches its terminal velocity. 

3.2.3 understand that objects moving against a resistive force may reach a terminal (constant) velocity

  • As discussed above, the total force acting on the object is given as 

                                                                                                F = mg – b\(v^{2}\)

  • When the drag force and gravitational force balance out, the object reaches its terminal velocity.

                                                                                                  mg = b\(v^{2}\)

  • This motion can be graphically represented as 
  •                                                                   
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