Force and Motion

Pulley

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  1. There are 2 types of pulley, the fixed pulley and the movable pulley.

(“Fixed pulley” by César Rincón available under a Creative Commons Attribution-Share Alike 3.0 Unported)
(“Movable pulley” by Johjak available under a Creative Commons Attribution-Share Alike 3.0 Unported)
  1. In SPM, we will only discuss the fixed pulley.
  2. The fixed pulley change the direction, without changing the magnitude of the force.
  3. In SPM, we assume all pulleys are smooth (no friction) unless it is stated otherwise.

Apparent Weight of an Object in a Lift

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  1. When a man standing inside an elevator, there are two forces acting on him.
    1. His weight, (W) which acting downward.
    2. Normal reaction (R), acting in the opposite direction of weight.
  2. The reading of the balance is equal to the normal reaction (R).
  3. Figure below shows the formula to calculate the reading of the balance at different situation.

Example 1:
Subra is standing on a balance inside an elevator. If Subra’s mass is 63kg, find the reading of the balance when the lift,

  1. stationary
  2. moving upward with a constant velocity, 15 ms-1.,
  3. moving upward with a constant acceleration, 1 ms-2.
  4. moving downward with a constant acceleration, 2 ms-2.

Answer:
a.

W = mg
W = (63)(10) = 630N

b.

W = mg
W = (63)(10) = 630N

c.

R = mg+ma
R = (63)(10)+(63)(1)
R = 693N

d.

R = mg−ma
R = (63)(10)−(63)(2)
R = 504N

 

Example 2:
A 54kg boy is standing in an elevator. Find the force on the boy’s feet when the elevator

  1. stands still
  2. moves downward at a constant velocity of 3 m/s
  3. decelerates downward with at 4.0 m/s2,
  4. decelerates upward withat 2.0 m/s2.

Answer:
a.

W = mg
W = (54)(10) = 540N

b.

W = mg
W = (54)(10) = 540N

c.

R=mg+ma
R=(54)(10)+(54)(4)
R=756N

d.

R=mg−ma
R=(54)(10)−(54)(2)
R=432N

 

Linear Motion

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  1. Kinematics is the research regarding the types of movement of an object without referring to the forces that cause the movement of the object.
  2. Movement along a straight line is called linear motion.
  3. Under the linear motion, we study the
    1. distance and displacement
    2. speed and velocity
    3. acceleration
      and the relationship between them.

SPM Form 4 Physics Chapter 2 – Force and Motion

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Chapter 2: Force and motion

  1. Linear Motion
    1. Distance and Displacement
    2. Speed and Velocity
    3. Acceleration
  2. Motion with Uniform Acceleration
  3. Ticker Timer and Ticker Tape
    1. Finding Velocity from Ticker Tape
    2. Finding Acceleration from Ticker Tape
  4. Graph of Motion
    1. Displacement-Time Graph
    2. Velocity-Time Graph
    3. Graph of Free Falling Object
  5. Mass and Inertia
    1. Applications of Effect of Inertia
  6. Momentum
    1. Principle of Conservation of momentum
    2. Elastic and Inelastic Collision
    3. Application of Momentum
  7. Effects of Force
  8. Types of Forces and Newton’s Third Law of Motion
  9. Impulse
  10. Impulsive Force
  11. Safety Features in Vehicles
  12. Gravity
    1. Free Falling
    2. Lift
    3. Pulley
  13. Vector Quantities
    1. Vector Addition
    2. Vector Resolution
    3. Inclined Plane
    4. Forces in Equilibrium
  14. Work
    1. Work Done by/Against the Gravity
    2. Finding Work Done from a Graph
  15. Energy
    1. Potential Energy
    2. Kinetic Energy
    3. Relationship between Energy and Work Done
  16. Power
    1. Efficiency
  17. Elasticity
    1. Hooke’s Law
    2. Spring
  18. Formulae List – Mind Map

Videos

  1. Introduction
  2. Distance vs Displacement – Part 1 | Part 2 | Example
  3. Speed and Velocity | Example
  4. Acceleration Part 1 | Part 2 | Example
  5. Positive and Negative Sign of Acceleration
  6. Analysing Acceleration
  7. Uniform Acceleration – Learning Focus
  8. Equation of Uniform Acceleration 
  9. Motion with Uniform Acceleration | Example 1 | Example 2 | Example 3 | Example 4 | Example 5
  10. Uniform Acceleration – Technique in Answering Calculation Questions
  11. Ticker Tape – Introduction
  12. Ticker Tape Timer
  13. Ticker Tape (Sample Question)
  14. Ticker Tape – Dots and Ticks
  15. Analysing Ticker Tape
  16. Ticker Tape Chart | Example 1
  17. Finding Time from a Ticker Tape
  18. Finding Velocity from a Ticker Tape – Part 1 | Part 2
  19. Finding Acceleration from a Ticker Tape
  20. Finding Acceleration from a Ticker Tape Chart
  21. Steps in Solving Linear Motion Problems – Part 1 (Common Mistake)
  22. Step in Solving Linear Motion Problems – Part 2 (Choose the Correct Equation)
  23. Step in Solving Linear Motion Problems – Part 3 (Substitution and solving the Equation)
  24. Steps in Solving Linear Motion Problems – Example 1 | Example 4
  25. Graph of Motion – Learning Focus
  26. Gradient of a Graph – Part 1 | Part 2
  27. Area Below the Graph
  28. Displacement-Time Graph | Continue
  29. Velocity-Time Graph | Continue
  30. Displacement – Time Graph (Exercise 1) | Exercise 2
  31. Velocity-Time Graph | Continue | Example
  32. Displacement-Time Graph to Velocity-Time Graph
  33. Acceleration-Time Graph – Part 1 | Part 2
  34. Graph of Free Falling – Part 1 | Part 2 | Part 3 | Part 4 |Part 5 | Part 6
  35. Mass and Inertia
  36. Momentum – Introduction
  37. Understanding Momentum – Part 1 | Part 2 | Part 3 |Part 4 | Part 5
  38. Principle of Conservation of Momentum – Introduction| The Equation | Summary of the Equations
  39. Applications Principle of Conservation of Momentum – Part 1 | Part 2
  40. Work Done
  41. Kinetic Energy
  42. Potential Energy
  43. Principle of Conservation of Energy
  44. Elasticity of Substances and Hooke’s Law
  45. Factors That Affect the Elasticity of Springs